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Mishra, ShashankDeveloping Novel Computational Fluid Dynamics Technique for Incompressible Flow and Flow Path Design of Novel Centrifugal Compressor
MS, University of Cincinnati, 2016, Engineering and Applied Science: Mechanical Engineering
The incompressible flow equations are function of the pressure gradients and not the pressure. The most important issue in solution of flow equations of incompressible fluid is the pressure gradient vector which is appearing as a source term in the momentum equation, but does not have any obvious equation coupling it with other dependent variables. Accurate numerical solutions are obtained for the incompressible Navier Stokes equations in primitive variables. Explicit finite difference scheme computer code is developed to solve incompressible flow equations. In this study, consistent with the physics of incompressible flows, the velocity and pressure gradient vectors are considered as the dependent variables. In this case, that satisfies continuity equation to machine zero, the pressure gradient vector increases the number of dependent variables which requires additional equations to close the system of governing equations. Additional equations are obtained by reformulating the continuity equation and adding a time derivative term for the pressure gradient. Upon, convergence of the numerical solution, the continuity equation will be satisfied to an arbitrary constant. To enforce that constant to be zero, the continuity equation is set to be zero on the boundary of the solution domain. It is important to note that the curl of the reformulated continuity equation automatically satisfies the curl of the pressure gradient identity. This scheme is applicable for two and three dimensions, inviscid and viscous flows. Multistage axial compressor has an advantage of lower stage loading as compared to a single stage. Several stages with low pressure ratio are linked together which allows for multiplication of pressure to generate high pressure ratio in an axial compressor.Since each stage has low pressure ratio they operate at a higher efficiency and the efficiency of multi-stage axial compressor as a whole is very high. Although, single stage centrifugal compressor has higher pressure ratio compared with an axial compressor but multistage centrifugal compressors are not as efficient because the flow has to be turned from radial at outlet to axial at inlet for each stage. The present study explores the advantages of extending the axial compressor efficient flow path that consist of rotor stator stages to the centrifugal compressor stage. In this invention, two rotating rows of blades are mounted on the same impeller disk, separated by a stator blade row attached to the casing. A certain amount of turning can be achieved through a single stage centrifugal compressor before flow starts separating, thus dividing it into multiple stages would be advantageous as it would allow for more flow turning. Flow characteristics of the novel multistage design are compared with a single stage centrifugal compressor. The flow path of the baseline and multi-stage compressor are created using 3DBGB tool and DAKOTA is used to optimize the performance of baseline as well novel design. The optimization techniques used are Genetic algorithm followed by Numerical Gradient method. The multi-stage compressor is more efficient with a higher pressure ratio compared with the base line design for the same work input and initial conditions

Committee:

Shaaban Abdallah, Ph.D. (Committee Chair); Clarissa Belloni, Ph.D. (Committee Member); Kumar Vemaganti, Ph.D. (Committee Member)

Subjects:

Mechanical Engineering; Mechanics

Keywords:

Incompressible flow solution;Numerical Modelling;Centrifugal Comopressor;Finite Difference Explicit Solver;Computational Fluid Dynamics;Continuity Equation

Krishnamoorthy, Mahesh kumaarInvestigations on Linkages Between Blood Flow Dynamics and Histological Endpoints in Dialysis Access Fistula
PhD, University of Cincinnati, 2010, Engineering : Mechanical Engineering
Arteriovenous (AV) fistula, a surgical connection created between an artery and a vein in order to increase the blood flow for dialysis, is currently the preferred mode of access. AV fistulae failure has been a major clinical problem. Among the factors contributing to AV fistula failure, the hemodynamics inside the AV fistula play a significant role. Though there have been several studies focusing on hemodynamics in AV fistula, there is still a gap in the understanding of the reasons for failure. Thus, the main objective of this study was to understand the factors responsible for fistula non-maturation and aggressive venous stenosis, in order to reduce their future failure rates. The underlying hypothesis of this research was that the hemodynamic forces and their alteration through change in anatomical configuration would eventually lead to change in the maturation rates and intima-media (IM) thickening.A pig model of AV fistula was developed in curved and straight configurations. Functional (flow rate, pressure) and anatomic (diameter, geometry) measurements were carried out using invasive and non-invasive techniques. Geometric modeling of the two configurations of AV fistula was performed. WSS at different time points and along different orientations of the venous wall were computed. With the help of radio-opaque markers, the WSS at all time points was correlated with the IM thickening at the sacrifice for the curved and straight AV fistulae for all the pigs. WSS immediately after AV fistula creation, showed an inverse correlation (r2=0.95) with the percentage stenosis at a 42 days in different anatomical regions from the initial IVUS studies. The effect of altering the configuration yielded significant difference in WSS. Curved fistula had a smaller difference in WSS between outer wall and inner wall locations. The histological specimens at 42 days showed that curved fistula had a uniform IM thickening pattern in the proximal vein. However, the straight configuration, which had large WSS difference between the outer and inner walls, had an eccentric pattern of IM thickening. The increase in the mean flow rate with time was greater in curved configuration (~ 4x) as compared to the straight configuration (~3x). There was also inadequate dilatation for the straight configuration as compared to significant dilatation in the curved (55% for straight vs 150% for curved). In addition, absolute levels of WSS were found to be inversely correlated with absolute values of IM thickening. Differences in WSS at opposite orientations were found to be directly correlated with the difference in IM thickness. The two way ANOVA procedure, yielded statistically significant differences (p<0.1) for the effect of configuration, time point on flow and diameter respectively. The results suggest linkages between WSS and the pattern of luminal stenosis and a correlation between configuration and the pattern of IM thickening. At a clinical level, these results suggest that it might be possible to alter the configuration, and consequently the WSS value in an AV fistula, using computer modeling prior to surgical placement. This could result in a reduction in clinical fistula failure.

Committee:

Rupak Banerjee, PhD, PE (Committee Chair); Kumar Vemaganti, PhD (Committee Member); Prabir Roy-Chaudhury, MD, PhD (Committee Member); Lois Arend, PhD, MD (Committee Member); Ronald Huston, PhD (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Hemodynamics;Wall shear stress;computational fluid dynamics;hemodialysis;fistula

Rose, Isaac D.Aerodynamic Modeling of an Unmanned Aerial Vehicle Using a Computational Fluid Dynamics Prediction Code
Master of Science (MS), Ohio University, 2009, Electrical Engineering (Engineering and Technology)
The process of creating a six degree-of-freedom model for an aerospace vehicle requires detailed knowledge of the aerodynamic characteristics. This thesis presents an implementation of a Computational Fluid Dynamics (CFD) predictioncomputer code to generate aerodynamic coefficients for the Brumby Mk. I Unmanned Aerial Vehicle (UAV). The aerodynamic coefficients include both the force and moment coefficients. These values are verified by creating a Matlab/Simulink six degree-of-freedom model.

Committee:

Douglas A. Lawrence, PhD (Advisor); Jerrel Mitchell, PhD (Committee Member); Jeffrey Dill, PhD (Committee Member); William Kaufman, PhD (Committee Member)

Subjects:

Aerospace Materials; Electrical Engineering; Engineering

Keywords:

Brumby; Computational Fluid Dynamics; DATCOM; Missile DATCOM; Aerodynamic Coefficients; Aircraft Model; six degree-of-freedom model

Crowell, Andrew RModel Reduction of Computational Aerothermodynamics for Multi-Discipline Analysis in High Speed Flows
Doctor of Philosophy, The Ohio State University, 2013, Aero/Astro Engineering
This dissertation describes model reduction techniques for the computation of aerodynamic heat flux and pressure loads for multi-disciplinary analysis of hypersonic vehicles. NASA and the Department of Defense have expressed renewed interest in the development of responsive, reusable hypersonic cruise vehicles capable of sustained high-speed flight and access to space. However, an extensive set of technical challenges have obstructed the development of such vehicles. These technical challenges are partially due to both the inability to accurately test scaled vehicles in wind tunnels and to the time intensive nature of high-fidelity computational modeling, particularly for the fluid using Computational Fluid Dynamics (CFD). The aim of this dissertation is to develop efficient and accurate models for the aerodynamic heat flux and pressure loads to replace the need for computationally expensive, high-fidelity CFD during coupled analysis. Furthermore, aerodynamic heating and pressure loads are systematically evaluated for a number of different operating conditions, including: simple two-dimensional flow over flat surfaces up to three-dimensional flows over deformed surfaces with shock-shock interaction and shock-boundary layer interaction. An additional focus of this dissertation is on the implementation and computation of results using the developed aerodynamic heating and pressure models in complex fluid-thermal-structural simulations. Model reduction is achieved using a two-pronged approach. One prong focuses on developing analytical corrections to isothermal, steady-state CFD flow solutions in order to capture flow effects associated with transient spatially-varying surface temperatures and surface pressures (e.g., surface deformation, surface vibration, shock impingements, etc.). The second prong is focused on minimizing the computational expense of computing the steady-state CFD solutions by developing an efficient surrogate CFD model. The developed two-pronged approach is found to exhibit balanced performance in terms of accuracy and computational expense, relative to several existing approaches. This approach enables CFD-based loads to be implemented into long duration fluid-thermal-structural simulations.

Committee:

Jack McNamara (Advisor); Thomas Eason, III (Committee Member); Jeffrey Bons (Committee Member); Mo-How Herman Shen (Committee Member); Mei Zhuang (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

Aerodynamic Heating; Pressure; Fluid-Thermal-Structural Analysis; Reduced Order Modeling; Surrogate Modeling; Computational Fluid Dynamics; Hypersonic; Supersonic; High-Speed Flow

Heberling, BrianA Numerical Analysis on the Effects of Self-Excited Tip Flow Unsteadiness and Upstream Blade Row Interactions on the Performance Predictions of a Transonic Compressor
MS, University of Cincinnati, 2017, Engineering and Applied Science: Aerospace Engineering
Computational fluid dynamics (CFD) simulations can offer a detailed view of the complex flow fields within an axial compressor and greatly aid the design process. However, the desire for quick turnaround times raises the question of how exact the model must be. At design conditions, steady CFD simulating an isolated blade row can accurately predict the performance of a rotor. However, as a compressor is throttled and mass flow rate decreased, axial flow becomes weaker making the capturing of unsteadiness, wakes, or other flow features more important. The unsteadiness of the tip clearance flow and upstream blade wake can have a significant impact on a rotor. At off-design conditions, time-accurate simulations or modeling multiple blade rows can become necessary in order to receive accurate performance predictions. Unsteady and multi- bladerow simulations are computationally expensive, especially when used in conjunction. It is important to understand which features are important to model in order to accurately capture a compressor’s performance. CFD simulations of a transonic axial compressor throttling from the design point to stall are presented. The importance of capturing the unsteadiness of the rotor tip clearance flow versus capturing upstream blade-row interactions is examined through steady and unsteady, single- and multi-bladerow computations. It is shown that there are significant differences at near stall conditions between the different types of simulations.

Committee:

Paul Orkwis, Ph.D. (Committee Chair); Shaaban Abdallah, Ph.D. (Committee Member); Mark Turner, Sc.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

computational fluid dynamics;turbomachinery;transonic compressor;cfd;compressor stall

Chatziefstratiou, EfthaliaSIMULATION OF TREE STEM INJURY, AIR FLOW AND HEAT DISPERSION IN FORESTS FOR PREDICTION OF FIRE EFFECTS
Doctor of Philosophy, The Ohio State University, 2015, Environmental Science
This work presents two computational tools, Firestem2D and the fire module of Regional Atmospheric Modelling System (RAMS)-based Forest Large Eddy Simulation (RAFLES), which will help to make predictions of fire effects on trees and the atmosphere. FireStem2D is a software tool for predicting tree stem heating and injury in forest fires. It is a physically-based, two-dimensional model of stem thermodynamics that results from heating at the bark surface. It builds on an earlier one-dimensional model (FireStem) and provides improved capabilities for predicting fire-induced mortality and injury before a fire occurs by resolving stem moisture loss, temperatures through the stem, degree of bark charring, and necrotic depth around the stem. The results of numerical parameterization and model evaluation experiments for FireStem2D that simulate laboratory stem-heating experiments of 52 tree sections from 25 trees are presented. A set of virtual sensitivity analysis experiments were also conducted to test the effects of unevenness of heating around the stem and with above ground height using data from two studies: a low-intensity surface fire and a more intense crown fire. The model allows for improved understanding and prediction of the effects of wildland fire on injury and mortality of trees of different species and sizes. Further, a study of the effects of particular properties of a high-resolution canopy resolving large eddy simulation (RAFLES) was conducted. RAFLES was later used to simulate the dispersion of heat and smoke inside and above forest canopies during low-intensity prescribed surface fires. RAFLES is the only large eddy simulation model that can resolve the effects of the volume of the trees in the canopy. All other models neglect the volume effects and only allow the flow to interact with the forest through a prescribed drag term. As a preliminary study for the heat dispersion simulations, the effects of resolving the tree volumes on air flow inside and around semi porous barriers, such as forests and cities were evaluated. The effects of the numerical representation of volume restriction, independent of the effects of the leaf drag were explicitly tested by comparing drag-only simulations, where neither volume nor aperture restrictions to the flow were prescribed, restriction-only simulations, where no drag was prescribed, and control simulations, where both drag and volume plus aperture restrictions were included. Finally, RAFLES was used to investigate how different canopy structures interact with augmented surface heat flux, simulating a low-intensity surface fire and how these interactions influence turbulence and heat exchange between canopy and atmosphere. A simplified, low-intensity fire event was simulated by directly prescribing heat flux to the bottom three grid layers of the simulation, below the canopy top. The effect of canopy structure on heat accumulation in the canopy and heat dispersion in and above canopy was tested. Furthermore, for each canopy structure, homogeneous and heterogeneous fire patterns were prescribed to contrast the effect of heterogeneity of the fire pattern with that of the canopy structure.

Committee:

Gil Bohrer, Prof. (Advisor)

Subjects:

Civil Engineering; Environmental Engineering; Environmental Science; Fluid Dynamics

Keywords:

heat transfer, atmospheric modeling, fire, turbulence, heat flux, air flow, fire effects, tree stem injury, smoke dispersion, large eddy simulations, computational fluid dynamics

Bilyeu, David LA HIGHER-ORDER CONSERVATION ELEMENT SOLUTION ELEMENT METHOD FOR SOLVING HYPERBOLIC DIFFERENTIAL EQUATIONS ON UNSTRUCTURED MESHES
Doctor of Philosophy, The Ohio State University, 2014, Mechanical Engineering
This dissertation presents an extension of the Conservation Element Solution Element (CESE) method from second- to higher-order accuracy. The new method retains the favorable characteristics of the original second-order CESE scheme, including (i) the use of the space-time integral equation for conservation laws, (ii) a compact mesh stencil, (iii) the scheme will remain stable up to a CFL number of unity, (iv) a fully explicit, time-marching integration scheme, (v) true multidimensionality without using directional splitting, and (vi) the ability to handle two- and three-dimensional geometries by using unstructured meshes. This algorithm has been thoroughly tested in one, two and three spatial dimensions and has been shown to obtain the desired order of accuracy for solving both linear and non-linear hyperbolic partial differential equations. The scheme has also shown its ability to accurately resolve discontinuities in the solutions. Higher order unstructured methods such as the Discontinuous Galerkin (DG) method and the Spectral Volume (SV) methods have been developed for one-, two- and three-dimensional application. Although these schemes have seen extensive development and use, certain drawbacks of these methods have been well documented. For example, the explicit versions of these two methods have very stringent stability criteria. This stability criteria requires that the time step be reduced as the order of the solver increases, for a given simulation on a given mesh. The research presented in this dissertation builds upon the work of Chang, who developed a fourth-order CESE scheme to solve a scalar one-dimensional hyperbolic partial differential equation. The completed research has resulted in two key deliverables. The first is a detailed derivation of a high-order CESE methods on unstructured meshes for solving the conservation laws in two- and three-dimensional spaces. The second is the code implementation of these numerical methods in a computer code. For code development, a one-dimensional solver for the Euler equations was developed. This work is an extension of Chang's work on the fourth-order CESE method for solving a one-dimensional scalar convection equation. A generic formulation for the nth-order CESE method, where n > 3, was derived. Indeed, numerical implementation of the scheme confirmed that the order of convergence was consistent with the order of the scheme. For the two- and three-dimensional solvers, SOLVCON was used as the basic framework for code implementation. A new solver kernel for the fourth-order CESE method has been developed and integrated into the framework provided by SOLVCON. The main part of SOLVCON, which deals with unstructured meshes and parallel computing, remains intact. The SOLVCON code for data transmission between computer nodes for High Performance Computing (HPC). To validate and verify the newly developed high-order CESE algorithms, several one-, two- and three-dimensional simulations where conducted. For the arbitrary order, one-dimensional, CESE solver, three sets of governing equations were selected for simulation: (i) the linear convection equation, (ii) the linear acoustic equations, (iii) the nonlinear Euler equations. All three systems of equations were used to verify the order of convergence through mesh refinement. In addition the Euler equations were used to solve the Shu-Osher and Blastwave problems. These two simulations demonstrated that the new high-order CESE methods can accurately resolve discontinuities in the flow field. For the two-dimensional, fourth-order CESE solver, the Euler equation was employed in four different test cases. The first case was used to verify the order of convergence through mesh refinement. The next three cases demonstrated the ability of the new solver to accurately resolve discontinuities in the flows. This was demonstrated through: (i) the interaction between acoustic waves and an entropy pulse, (ii) supersonic flow over a circular blunt body, (iii) supersonic flow over a guttered wedge. To validate and verify the three-dimensional, fourth-order CESE solver, two different simulations where selected. The first used the linear convection equations to demonstrate fourth-order convergence. The second used the Euler equations to simulate supersonic flow over a spherical body to demonstrate the scheme's ability to accurately resolve shocks. All test cases used are well known benchmark problems and as such, there are multiple sources available to validate the numerical results. Furthermore, the simulations showed that the high-order CESE solver was stable at a CFL number near unity.

Committee:

Sheng-Tao (John) Yu (Advisor); Jean-Luc Cambier (Committee Member); Chau-Lyan Chang (Committee Member); Sin-Chung Chang (Committee Member); A. Terrence Conlisk (Committee Member); Datta Gaitonde (Committee Member); Ahmet Selamet (Committee Member)

Subjects:

Aerospace Engineering; Mechanical Engineering

Keywords:

Computational Fluid Dynamics; CFD; CESE; Higher Order; Unstructured

Galbraith, Marshall CA Discontinuous Galerkin Chimera Overset Solver
PhD, University of Cincinnati, 2013, Engineering and Applied Science: Aerospace Engineering
This work summarizes the development of an accurate, efficient, and flexible Computational Fluid Dynamics computer code that is an improvement relative to the state of the art. The improved accuracy and efficiency is obtained by using a high-order discontinuous Galerkin (DG) discretization scheme. In order to maximize the computational efficiency, quadrature-free integration and numerical integration optimized as matrix-vector multiplications is employed and implemented through a pre-processor (PyDG). Using the PyDG pre-processor, a C++ polynomial library has been developed that uses overloaded operators to design an efficient Domain Specific Language (DSL) that allows expressions involving polynomials to be written as if they are scalars. The DSL, which makes the syntax of computer code legible and intuitive, promotes maintainability of the software and simplifies the development of additional capabilities. The flexibility of the code is achieved by combining the DG scheme with the Chimera overset method. The Chimera overset method produces solutions on a set of overlapping grids that communicate through an exchange of data on grid boundaries (known as artificial boundaries). Finite volume and finite difference discretizations use fringe points, which are layers of points on the artificial boundaries, to maintain the interior stencil on artificial boundaries. The fringe points receive solution values interpolated from overset grids. Proper interpolation requires fringe points to be contained in overset grids. Insufficient overlap must be corrected by modifying the grid system. The Chimera scheme can also exclude regions of grids that lie outside the computational domain; a process commonly known as hole cutting. The Chimera overset method has traditionally enabled the use of high-order finite difference and finite volume approaches such as WENO and compact differencing schemes, which require structured meshes, for modeling fluid flow associated with complex geometries. The large stencil associated with these high-order schemes can significantly complicate the inter-grid communication and hole cutting processes. Unlike these high-order schemes, the DG method always retains a small stencil regardless of the order of approximation. The small stencil of the DG method simplifies the inter-grid communication scheme as well as hole cutting procedures. The DG-Chimera scheme does not require a separate interpolation method because the DG scheme represents the solution as cell local polynomials. Hence, the DG-Chimera method does not require fringe points to maintain the interior stencil across inter-grid boundaries. Thus, inter-grid communication can be established as long as the receiving boundary is enclosed by or abuts the donor mesh. This makes the inter-grid communication procedure applicable to both Chimera and zonal meshes. The small stencil implies hole cutting can be performed without regard to maintaining a minimum stencil and thereby greatly simplifies hole cutting. Hence, the DG-Chimera scheme has the potential to greatly simplify the overset grid generation process. Furthermore, the DG-Chimera scheme is capable of using curved cells to represent geometric features. The curved cells resolve issues associated with linear Chimera viscous meshes used for finite volume and finite difference schemes. Finally, the convergence rate of the Chimera schemes is dramatically increased by linearization of the inter-grid communication.

Committee:

Paul Orkwis, Ph.D. (Committee Chair); John A. Benek, Ph.D. (Committee Member); Shaaban Abdallah, Ph.D. (Committee Member); Mark Turner, Sc.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Computational Fluid Dynamics;Discontinuous Galerkin;Chimera Method;High Order Methods

MAHALATKAR, KARTIKEYACAVITATING FLOW OVER OSCILLATING HYDROFOILS AND HYDROFOIL-BASED SHIP STABILIZATION SYSTEM
MS, University of Cincinnati, 2006, Engineering : Mechanical Engineering
Hydrofoils are used in maritime applications; such as ships and submarines, for stabilization, maneuvering, etc. In many of these applications, the hydrofoil may experience dynamic motion; an example would be an active-fin ship stabilization system where the hydrofoil oscillates periodically at large angles of attack. Computational Fluid Dynamics (CFD) is used for simulating the flow over an oscillating hydrofoil used in such systems. The CFD simulations for oscillating-hydrofoil flow are used in analysis of performance of the active-fin ship stabilization system. A system model has been created in MATLAB for this purpose. A Proportional Integral Derivative (PID) control system has also been developed to control the fin motion. Simulation of the active-fin ship-stabilization system in MATLAB provides the typical motion experienced by a hydrofoil used in ship stabilization. This motion is fed back to a CFD solver to determine the effect of non-sinusoidal oscillation on Lift, Drag and Moment of the hydrofoil. The aerodynamics of the non-sinusoidally oscillating hydrofoil is analyzed so as to find an optimum pitching motion for the hydrofoil so as to produce higher lift forces and thus provide better performance. Another important aspect which affects the performance of an active-fin ship stabilization system is cavitation occurring in the flow over oscillating hydrofoils. Cavitation occurs because the pressure on the suction side of the hydrofoil falls below the vapor pressure of water. Numerical simulations using Reynolds-averaged Navier-Stokes equations are carried out to analyze the effect of cavitation on the dynamic stall of an oscillating hydrofoil. It was found that the flow physics changes considerably with cavitation. The dynamic stall vortex (DSV) was formed at an angle of attack much smaller than that for the non-cavitating case. The vortical structures were found to be distorted as compared to the non-cavitating case. Cavitation led to large oscillations in coefficient of lift, drag and moment during the downward pitching motion and this can adversely affect the system.

Committee:

Dr. Urmila Ghia (Advisor)

Keywords:

CFD; Fluid dynamics; Computational fluid dynamics; Cavitation; Ship stabilization; active fin ship stabilization

Sun, HuaweiTheoretical and experimental study of a high rise hog building for improved utilization and environmental quality protection
Doctor of Philosophy, The Ohio State University, 2004, Food, Agricultural, and Biological Engineering
Ammonia and liquid waste problems are a great concern for animal producers because of their environmental impacts and effects on human and animal health. A novel swine production system, the High-Rise™ Hog Building (HRHB), has been developed to minimize liquid waste, reduce nutrient losses and control ammonia volatilization. A theoretical and experimental study was done to evaluate nutrient losses and ammonia levels in a HRHB and associate manure management system. Two groups of hogs, 998 head in summer and 1047 head in winter were studied. Animals grew well with an average weight gain rate of 0.86 kg/pig/day (1.89 lb/pig/day). The feed was consumed at a rate of 2.4 kg/pig/day (5.3 lb/pig/day). The average nitrogen, phosphorous and potassium losses due to volatilization (N) and liquid drainage (N, P, K) from the HRH building in both summer and winter periods were 3.86kg/head, 0.25 kg/head and 0.76 kg/head, representing 52, 21 and 47% of the initial amount respectively. Ammonia concentrations in the pig space were less than 2.5 ppm in summer and as high as 30 ppm in winter. Average ammonia concentration in winter was 16 ppm. A one-way ANOVA model and two linear regression models were developed that showed lower outdoor temperature and higher indoor/outdoor temperature difference could lead to higher ammonia concentrations in pig space in winter. The p-values were calculated less than 0.001. Computational Fluid Dynamics (CFD) models were developed and validated to investigate airflow pattern and ammonia distribution in HRHB. In winter, the CFD models predicted that some air blown through the manure bed could flow up into the pig space, which could lead to high ammonia concentrations in the upper level of the building. To reduce ammonia concentration in the pig space, 3-D non-isothermal CFD models were used to optimize the ventilation system of the HRHB. The aeration used to dry manure bedding was predicted as a significant factor to cause high ammonia concentration in the pig space. A comparative assessment of HRHB system versus other alternative hog production systems will be done in the future.

Committee:

Frederick Michel Jr. (Advisor)

Keywords:

Hog Manure; High Rise Hog Building; Ammonia; Computational Fluid Dynamics; CFD modeling; Waste management; Mass balance; Air quality; Ventilation; Animal facility; Nutrient loss

Bork, Carrington E.Aerodynamic Development of the Buckeye Bullet 3 Electric Landspeed Vehicle
Master of Science, The Ohio State University, 2012, Mechanical Engineering
For almost two decades The Ohio State University’s electric motorsports teams have been winning races and setting records. The OSU student designed Buckeye Bullet was the first electric car to reach speeds in excess of 300 mph. The Buckeye Bullet 2 was the first hydrogen powered car to break 300 mph and the team would eventually hold the record for the world’s fastest electric car with the Buckeye Bullet 2.5. The team of students is now setting its sights on reaching over 400 mph using advanced lithium ion batteries in a completely new vehicle, the Buckeye Bullet 3. At these high speeds aerodynamics play a crucial role in determining the vehicle performance and safety. This thesis presents the aerodynamic development of the Buckeye Bullet 3 and its role in shaping the future of land speed racing.

Committee:

Giorgio Rizzoni (Advisor); Mei Zhuang (Committee Member)

Subjects:

Aerospace Engineering; Engineering; Mechanical Engineering

Keywords:

aerodynamics; CFD; landspeed; racing; Buckeye Bullet; computational fluid dynamics; electric vehicle; fastest electric car;

Li, ZhisongAdvanced Computational Modeling for Marine Tidal Turbine Farm
PhD, University of Cincinnati, 2012, Engineering and Applied Science: Aerospace Engineering

In the global effort of exploring low-cost renewable energy and reducing greenhouse gas emissions, energy sources in the ocean are receiving more and more attentions. The kinetic energy from ocean currents is enormous and virtually inexhaustible. Among the different kinds of ocean currents, the tidal flow is most predictable and sufficiently rapid for power generation to many well-chosen sites. To convert the stream momentum into electrical power, a device called marine tidal turbine, predominantly horizontal-axis, is used. Working like a windmill underwater, the tidal turbine operates in a unique environment constrained by water-free surfaces and seabeds. The present study will concentrate on the numerical modeling of tidal turbine operations in standalone and array configurations. Dedicated computational fluid dynamics (CFD) models are first created for this particular research application. Based on the solutions obtained from simulations, comparative investigations are then taken to assess the wake characteristics in a turbine farm scenario in order to minimize any unfavorable wake/turbine interactions. The effects of free surface waves and uneven bed terrains are also studied.

To establish the simulations, one steady and one time-transient code are developed using modular programming and parallel processing design. The core solver uses a classic projection method to solve the three-dimensional incompressible flow problem and an efficient s-coordinate method to model the free surface, both of which are well verified with analytical solutions. An actuator disc model and an actuator line model are numerically implemented for the steady and unsteady codes respectively, validated by experimental data. To include the natural water waves and ambient turbulence unsteadiness, the inflow boundary condition in time-transient code incorporates a fifth-order Stokes wave generator and artificial velocity fluctuations. Foreseeing the rotational movements and anisotropic turbulence from turbine spinning, a second-moment closure or nonlinear eddy viscosity assumption is needed for turbulence modeling. The project adopts an explicit algebraic Reynolds stress model, balancing the demand for solution accuracy and computational economy.

Extensive tests and case running have been performed using the simulation codes with parametric modifications for different evaluation purposes. In scalability tests, both codes can give acceptable speedup up to 30 nodes and the steady state code achieves better performance due to its highly explicit formulations. The steady and unsteady codes are compared as baselines cases and they agree well in predicting wake velocity deficits. In steady state modeling of a single turbine, the study appraises the influence on turbine wake from rotor size, inflow profiles, and three different simple bed terrains. In unsteady modeling, turbine wake under long waves exhibits some velocity superposition behavior. Turbine array simulations first probe the steady state flow features in a number of rotor configurations: side-by-side, transverse, streamwise, co-rotating, and contra-rotating. They are examined for their wake restoration rates and turbulence intensities. Then the time-averaged wake activities in the staggering and tilted line layout are inspected and compared to settle a fluid dynamic preference. Finally an unsteady modeling is carried out for a pair of upstream-downstream and contra-rotating rotors, enabling a dynamic analysis on the turbine interactions.

Committee:

Kirti Ghia, PhD (Committee Chair); Scott Schreck, PhD (Committee Member); Shaaban Abdallah, PhD (Committee Member); Urmila Ghia, PhD (Committee Member)

Subjects:

Energy

Keywords:

Computational Fluid Dynamics;Marine Tidal Turbine Farm;Actuator Disc;Actuator Line;Free Surface Wave;Parallel Computation;

Sharpe, Jacob Andrew3D CFD Investigation of Low Pressure Turbine Aerodynamics
Master of Science in Mechanical Engineering (MSME), Wright State University, 2017, Mechanical Engineering
A 3-D Reynolds-Averaged Navier Stokes (RANS) model of a highly-loaded blade profile has been developed using a commercial CFD code with an unstructured/structured grid and several different turbulence models. The ability of each model to predict total pressure loss performance is examined in terms of the spanwise loss distribution and the integrated total pressure loss coefficient. The flowfield predicted by each model is investigated through comparisons of isosurfaces of Q criterion to previous Implicit Large Eddy Simulation (ILES) results. The 3-equation k-kl-¿ model was shown to provide the most accurate performance predictions for a baseline 3-D LPT geometry, and was then used to analyze the effect a new 3D contoured geometry. The model accurately predicted the qualitative improvement made by the contour by weakening the various vortex structures.

Committee:

Mitch Wolff, Ph.D. (Advisor); Rolf Sondergaard, Ph.D. (Committee Member); Rory Roberts, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics

Keywords:

Computational fluid dynamics; aerodynamics; turbomachinery; low pressure turbines

Holden, Jacob R.Experimental Testing and Computational Fluid Dynamics Simulation of Maple Seeds and Performance Analysis as a Wind Turbine
MS, University of Cincinnati, 2016, Engineering and Applied Science: Aerospace Engineering
Descending maple seeds generate lift to slow their fall and remain aloft in a blowing wind; have the wings of these seeds evolved to descend as slowly as possible? A unique energy balance equation, experimental data, and computational fluid dynamics simulations have all been developed to explore this question from a turbomachinery perspective. The computational fluid dynamics in this work is the first to be performed in the relative reference frame. Maple seed performance has been analyzed for the first time based on principles of wind turbine analysis. Application of the Betz Limit and one-dimensional momentum theory allowed for empirical and computational power and thrust coefficients to be computed for maple seeds. It has been determined that the investigated species of maple seeds perform near the Betz limit for power conversion and thrust coefficient. The power coefficient for a maple seed is found to be in the range of 48 - 54% and the thrust coefficient in the range of 66 - 84%. From Betz theory, the stream tube area expansion of the maple seed is necessary for power extraction. Further investigation of computational solutions and mechanical analysis find three key reasons for high maple seed performance. First, the area expansion is driven by maple seed lift generation changing the fluid momentum and requiring area to increase. Second, radial flow along the seed surface is promoted by a sustained leading edge vortex that centrifuges low momentum fluid outward. Finally, the area expansion is also driven by the spanwise area variation of the maple seed imparting a radial force on the flow. These mechanisms result in a highly effective device for the purpose of seed dispersal. However, the maple seed also provides insight into fundamental questions about how turbines can most effectively change the momentum of moving fluids in order to extract useful power or dissipate kinetic energy.

Committee:

Mark Turner, Sc.D. (Committee Chair); Shaaban Abdallah, Ph.D. (Committee Member); Paul Orkwis, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Maple seed;Computational Fluid Dynamics;Turbomachinery;Wind Turbine;Betz Limit;Boimimicry

Dehner, Richard D.An Experimental and Computational Study of Surge in Turbocharger Compression Systems
Doctor of Philosophy, The Ohio State University, 2016, Mechanical Engineering
The objective of the present study is to predict compression system surge instabilities, including discrete sound peaks at low frequencies and their amplitudes at key locations. One-dimensional (1D) gas dynamics models were created for a turbocharger stand and a twin, parallel turbocharged V6 gasoline turbocharged direct injection (GTDI) engine, which have a common turbocharger design. In addition, a three-dimensional (3D) computational fluid dynamics (CFD) model was developed for the compression system of the turbocharger stand, and prediction results are utilized to study the details of compressor flow-field breakdown and the resulting instabilities at reduced flow rates. The turbocharger stand isolated surge from engine airborne pulsations, thereby providing a simplified bench-top environment for in-depth studies of pertinent physics and model development. Two different compression system configurations were studied on the turbocharger stand. The first configuration incorporated a plenum (large volume), which produced surge as the flow rate was reduced. To facilitate surge predictions, a compressor performance map from an extended flow range small volume system (second configuration) was incorporated into a 1D model of the large volume configuration. Mild and deep surge predictions were completed with the 1D model of the large volume turbocharger stand compression system and the dominant sound peaks of simulations agreed reasonably well with the corresponding measurements. Engine experiments and modeling were carried out in two phases, where the first phase was steady-state, full load operation at low engine speeds and the second phase perturbed one of the compressors into surge. The engine model incorporated loss coefficients from flow bench experiments with induction system components, and modified air cleaner box and charge air cooler models that accurately captured the frequency dependent interaction of pressure waves. Steady-state engine data confirmed the accuracy of predicted performance, pressure drops, and wave dynamics in the induction system. Once the models for compressor surge and stable engine operation were independently validated with experimental data from the turbocharger stand and engine dynamometer, respectively, the engine model was then utilized for predictions with the right-bank compressor in both mild and deep surge. The mild surge prediction provided reasonable agreement with experimental data, and the accuracy of predictions improved as the load was increased and the right-bank compressor entered deep surge. Simulations with a 3D CFD model were initially performed during stable operation with a domain that was confined to the compressor with short inlet and outlet duct extensions. Resulting predictions agreed well with measurements from the turbocharger stand, including compressor performance and the onset of temperature rise near the inducer blade tips. Next, the computational domain was expanded to include the (full) large volume turbocharger stand compression system. As the compressor flow rate was reduced below that at the peak pressure ratio, rotating stall cells formed near the shroud-side diffuser wall. A further reduction in flow rate resulted in the system entering mild surge, where two cycles were simulated. Mild surge predictions from this CFD model provided good agreement with compressor inlet and outlet pressure measurements, in terms of reproducing the amplitude and frequency.

Committee:

Ahmet Selamet (Advisor); Jen-Ping Chen (Committee Member); Sandip Mazumder (Committee Member); Junmin Wang (Committee Member); Philip Keller (Committee Member)

Subjects:

Acoustics; Aerospace Engineering; Automotive Engineering; Engineering; Experiments; Fluid Dynamics; Mechanical Engineering; Transportation

Keywords:

turbocharger; automotive; internal combustion engine; engine; centrifugal compressor; compressor; instabilities; surge; rotating stall; one-dimensional model; three-dimensional computational fluid dynamics; 3D CFD

Kucukal, ErdemEXPERIMENTAL AND CFD INVESTIGATIONS OF THE FLUID FLOW INSIDE A HYDROCYCLONE SEPARATOR WITHOUT AN AIR CORE
Master of Sciences, Case Western Reserve University, 2015, EMC - Mechanical Engineering
Hydrocyclone separators are used in various industrial applications such as mineral processing in order to separate solid particles or liquid droplets from multiphase systems. A large number of studies have been conducted in recent years for understanding the flow characteristics within a cyclone. The currently available theoretical models only provide a limited amount of information regarding the cyclone performance and not applicable to most real-life applications. In this thesis, the single-phase fluid flow through a hydrocyclone was investigated by means of both computational and experimental techniques (Particle Image Velocimetry). The computational modelling was carried out using a commercial Computational Fluid Dynamics (CFD) code, Star CCM+. A mesh domain with more than 700k unstructured cells was created in a Cartesian coordinate system. Two turbulence models were used during the numerical calculations: The k-w model (with the curvature xvi correction) and the Reynolds Stress Model. In both cases, the first order discretization scheme was unable to resolve the flow field accurately due to the high levels of numerical dissipation. The velocity and pressure contours on various planes were drawn for both turbulence models, which showed the superiority of the RSM over the k-w model in the computational simulation of highly swirling flows. Particle Image Velocimetry (PIV) was used for the experimental investigations of the flow inside an optically clear hydrocyclone. The refractive index of the working fluid was matched to that of the model cyclone material, which was acrylic plastic, in order to prevent any optical distortions in the test setup. The refractive index matching was accomplished by using a sodium iodide solution (63.3 % NAI by weight). 10 µm silver coated hollow glass spheres were injected into the system as tracing particles. Investigations of the flow field were performed on two different regions of interest, and the first region was divided into seven fields of view (FOV). The results show that the radial-tangential velocities tend to increase from the cyclone wall to the vortex finder and reach a maximum value before they began to decline rapidly and eventually become zero on the wall. The experimental data were used to validate the numerical results both on a global level and based upon local velocity profiles. The comparisons showed that the two models were in good agreement particularly in the near-wall regions.

Committee:

Jaikrishnan Kadambi (Advisor)

Subjects:

Mechanical Engineering

Keywords:

Hydrocyclone, Particle Image Velocimetry, computational fluid dynamics, turbulence, swirling flows

Ingraham, DanielVerification of a Computational Aeroacoustics Code Using External Verification Analysis (EVA)
Master of Science in Mechanical Engineering, University of Toledo, 2010, College of Engineering
As Computational Aeroacoustics (CAA) codes become more complex andwidely used, robust Verification of such codes becomes more and more important. Recently, Hixon et al. proposed a variation of the Method of Manufactured Solutions of Roache especially suited for Verifying unsteady CFD and CAA codes that does not require the generation of source terms or any modification of the code being Verified. This work will present the development of the External Verification Analysis (EVA) method and the results of its application to some popular model equations of CFD/CAA and a high-order nonlinear CAA code.

Committee:

Ray Hixon, PhD (Committee Chair); Douglas Oliver, PhD (Committee Member); Chunhua Sheng, PhD (Committee Member)

Subjects:

Acoustics; Mechanical Engineering

Keywords:

Computational Aeroacoustics; Computational Fluid Dynamics; Code Verification; External Verification Analysis; Method of Manufactured Solutions; CAA; CFD; EVA; MMS

Kamarajugadda, Sai K.Advanced Models for Predicting Performance of Polymer Electrolyte Membrane Fuel Cells
Doctor of Philosophy, The Ohio State University, 2012, Mechanical Engineering
The primary objective of this study is to develop a multi-scale computational fluid dynamics (CFD) model to predict the performance of a polymer electrolyte membrane fuel cell (PEMFC). In particular, two critical factors affecting PEMFC performance, namely water and current transport through the polymer electrolyte membrane, and the effect of the cathode catalyst layer structure and composition are examined in detail. The implementation of phenomenological membrane models within CFD codes requires coupling of the conservation equation for the so-called water content within the membrane to the conservation equations for species mass outside the membrane. The first part of this dissertation investigates the accuracy and efficiency of various strategies for implementing phenomenological membrane models within the framework of a CFD code for prediction of the overall PEMFC performance. First, three popular phenomenological membrane models are investigated, and the accuracy of each model is assessed by comparing predicted results against experimental data. Results indicate that the Springer model and the Nguyen and White model over-predict the drying of the membrane, while the Fuller and Newman model provides the best match with experimental data. Following these studies, three strategies for implementation of the membrane model are investigated: (1) two-dimensional (2D) transport of water and current in membrane, (2) one-dimensional (1D) transport and (3) 1D transport with approximate transport properties. Fuller and Newman’s membrane model is used for these studies. The results obtained using the three approaches are found to be within 4% of each other, while there is no significant difference in the computational time required by the three strategies, indicating that an analytical 1D transport model for the membrane that uses approximate properties is adequate for describing transport through it. In the second part of the dissertation, the effect of the cathode catalyst layer’s structure and composition on the overall performance of a PEMFC is investigated. The starting point of this investigation is the well-known flooded agglomerate model, which is generalized to address the effects of ionomer (Nafion) loading, catalyst (platinum) loading, platinum/carbon ratio, cathode layer thickness, and agglomerate size and shape. Initially, spherical agglomerates are considered. This allows for an analytical solution of the governing equations. Following this, the model is generalized in order to account for arbitrary agglomerate shapes. The generalized flooded agglomerate model is first validated against previously published results, and then used to study the effect of the agglomerate shape (single sphere vs. intersecting spheres) and size on the oxidation reduction reaction (ORR) rate at the agglomerate scale. Results from the agglomerate scale studies indicate that the current per unit volume generated by the agglomerates is proportional to the surface-area-to-volume ratio of the agglomerates. It shows that, for a given agglomerate volume, the ORR is more efficient for non-spherical agglomerates than for spherical agglomerates. The generalized flooded agglomerate model provides the current generated per unit volume at the agglomerate scale, which is much smaller than a typical control volume used in CFD calculations of the overall PEMFC, i.e., it is a sub-grid scale model. This sub-grid scale agglomerate model is then embedded within a 2D CFD code for the prediction of the overall performance of the fuel cell. In order to do so, lookup tables are first generated and logarithmic interpolation is used. The integrated model is used to explore a wide range of the compositional and structural parameter space, mentioned earlier. In each case, the model is able to correctly predict the trends observed by past experimental studies. It is found that the performance trends are often different at intermediate versus high current densities – the former being governed by agglomerate-scale (or local) losses, while the latter is governed by catalyst layer thickness-scale (or global) losses. The presence of an optimal performance with varying Nafion content in the cathode is more due to the local agglomerate-scale mass transport and conductivity losses in the polymer coating around the agglomerates than due to the amount of Nafion within the agglomerate. It is also found that platinum mass loading needs to be at a moderate level in order to optimize fuel cell performance, even if cost is to be disregarded. For agglomerates of small size, the shape of the agglomerate is found to have a smaller effect on overall PEMFC performance than for agglomerates of larger size. The results from this dissertation provide, for the first time, a quantitative confirmation of the assumption of 1D transport of water and current within the membrane. Second, the generalized flooded agglomerate model developed as part of this dissertation presents a new framework for incorporating cathode structure and composition into full-scale CFD models for predicting PEMFC performance.

Committee:

Sandip Mazumder (Advisor); A Terrence Conlisk, Jr (Committee Member); Yann Guezennec (Committee Member); Vishwanath Subramaniam (Committee Member)

Subjects:

Chemical Engineering; Energy; Engineering; Mechanical Engineering

Keywords:

Polymer Electrolyte Membrane; Fuel Cell; Computational Fluid Dynamics; Cathode Catalyst Layer; Flooded Agglomerate; Membrane Transport; oxygen reduction reaction; ORR; modeling

Votaw, Zachary StevenComputational Study on Micro-Pilot Flame Ignition Strategy for a Direct Injection Stratified Charge Rotary Engine
Master of Science in Engineering (MSEgr), Wright State University, 2012, Mechanical Engineering
The Office of Security of Defense's Assured Fuels Initiative has recently been pressing for a single fuel battle space. This endeavor requires modifying many of the vehicle power plants currently in operation throughout the Armed Forces. The RQ-7 Shadow, an unmanned aerial vehicle (UAV) utilized by the Marine Corp and Army for reconnaissance purposes, is powered by UEL's AR741 rotary engine and functions on aviation fuel. One effort underway has been focused on developing this rotary engine system to operate on heavy fuels using direct injection technology and charge stratification. Although the rotary engine has many advantages over standard reciprocating engines, providing a reliable ignition source for the stratified charge within the sweeping combustion chamber presents challenges. This work made effort to compensate for those challenges by utilizing a pilot flame ignition system. The system incorporated a micro-diesel injector and spark plug recessed within an ignition cavity along the housing of the rotary engine. The pilot flame ignition approach was thoroughly evaluated by conducting a parametric study using computational methods to simulate the combustion process. Gambit meshing software was used to build the 3D rotary engine mesh. ANSYS Fluent was used to formulate and apply the various numerical models describing the combustion phenomena. And lastly, JMP software was used to perform a response surface analysis in effort to determine the optimal parameter values for the ignition system. The goal of the parametric study was to maximize power output and likewise minimize specific fuel consumption. A total of thirty one cases were performed to complete the study. For the rotary engine operating at 6000rpm an optimal solution was successfully realized within the design space. The rotary engine model generated 5.313 horsepower (HP) for the complete cycle of one chamber. The overall equivalency ratio allocated in the combustion chamber for the simulations was 0.55. This resulted in a specific fuel consumption of 0.395 lb/hp-h. The study not only provided evidence to confirm the profitable use of a pilot flame ignition system applied to the direct injection stratified charge rotary engine (DISCRE), but also provided multiple insights on the design and operation of such a system.

Committee:

Haibo Dong, PhD (Advisor); Rory Roberts, PhD (Committee Member); Greg Minkiewicz, PhD (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

CFD; Rotary Engine; Wankel Engine; Stratified Charge; Direct Injection; Pilot Flame Ignition; Multi-fuel; Parameter Optimization; Combustion Simulation; Computational Fluid Dynamics

Guarendi, Andrew NNumerical Investigations of Magnetohydrodynamic Hypersonic Flows
Master of Science, University of Akron, 2013, Mechanical Engineering
Numerical simulations of magnetohydrodynamic (MHD) hypersonic flow are presented for both laminar and turbulent flow over a cylinder and flow entering a scramjet inlet. ANSYS CFX is used to carry out calculations for steady flow at hypersonic speeds (Mach number > 5). The low magnetic Reynolds number (<<1) calculated based on the velocity and length scales in this problem justifies the quasistatic approximation, which assumes negligible effect of velocity on magnetic fields. Therefore the governing equations employed in the simulations are the compressible Navier-Stokes and the energy equations with MHD-related source terms such as Lorentz force and Joule dissipation. Turbulence effects are accounted for when applicable and multiple turbulence models are compared. The results demonstrate the ability of the magnetic field to affect the flowfield, and variables such as location and magnitude of the applied magnetic field are examined. An examination of future work is provided through the implementation of a semi-discrete central scheme in-house code toward the solution of the Orszag-Tang vortex system.

Committee:

Abhilash Chandy, Dr. (Advisor); Scott Sawyer, Dr. (Committee Member); Alex Povitsky, Dr. (Committee Member)

Subjects:

Aerospace Engineering; Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

Hypersonic; Hypersonic Flow; Flow over a cylinder; Magnetohydrodynamic; MHD; Lorentz; Hypersonic MHD; Numerical Methods; CFD; Computational fluid dynamics; fluid dynamics; Aerospace;

Farbos De Luzan, CharlesNumerical Analysis of Turbulent Flows in Channels of Complex Geometry
PhD, University of Cincinnati, 2016, Engineering and Applied Science: Aerospace Engineering
The current study proposes to follow a systematic validated approach to applied fluid mechanics problems in order to evaluate the ability of different computational fluid dynamics (CFD) to be a relevant design tool. This systematic approach involves different operations such as grid sensitivity analyses, turbulence models comparison and appropriate wall treatments, in order to define case-specific optimal parameters for industrial applications. A validation effort is performed on each study, with particle image velocimetry (PIV) experimental results as the validating metric. The first part of the dissertation lays down the principles of validation, and presents the details of a grid sensitivity analysis, as well as a turbulence models benchmark. The models are available in commercial solvers, and in most cases the default values of the equations constants are retained. The validation experimental data is taken with a hot wire, and has served as a reference to validate multiple turbulence models for turbulent flows in channels. In a second part, the study of a coaxial piping system will compare a set of different steady Reynolds-Averaged Navier Stokes (RANS) turbulence models, namely the one equation model Spalart-Almaras, and two-equation-models standard k-epsilon, k-epsilon realizable, k-epsilon RNG, standard k-omega, k-omega SST, and transition SST. The geometry of interest involves a transition from an annulus into a larger one, where highly turbulent phenomena occur, such as recirculation and jet impingement. Based on a set of constraints that are defined in the analysis, a chosen model will be tested on new designs in order to evaluate their performance. The third part of this dissertation will address the steady-state flow patterns in a Viscosity-Sensitive Fluidic Diode (VSFD). This device is used in a fluidics application, and its originality lies in the fact that it does not require a control fluid in order to operate. This section will discuss the treatment of viscosity in a steady RANS model, and will provide observations that will support the design of an improved device. The fourth part of the document will address the unsteady-state flow patterns in a Bi-Stable Valve (BSV) activated by fluids of different viscosities. This device involves a bi-stable behavior, referred to as the switch, which actuation depends on the viscosity of the fluid. This section will discuss the dependence of initial conditions in unsteady flow simulations, and will provide observations that will support the design of an improved device. In a fifth and final part, compressible large eddy simulation is employed to numerically investigate the laryngeal flow. Symmetric static models of the human larynx with a divergent glottis are considered, with the presence of False Vocal Folds (FVFs). The FVFs are a main factor affecting the closure of the TVFs. The direct link between the FVFs geometry and the motion of the TVFs, and by extension to the voice production, is of interest for medical applications as well as future research works. The presence of the FVFs also changes the dominant frequencies in the velocity and pressure spectra.

Committee:

Ephraim Gutmark (Committee Chair); Shaaban Abdallah (Committee Member); Mark Turner (Committee Member)

Subjects:

Aerospace Materials

Keywords:

aerodynamics;fluidics;computational fluid dynamics;turbulence modeling

Seidu, IddrisuAnalytical and Numerical Validation of Nozzle Spray Measurement Data Obtained from a Newly Developed Production System
Master of Science in Mechanical Engineering, Cleveland State University, 2015, Washkewicz College of Engineering
A newly developed production test stand for measuring the spray angle of a pressure swirl atomizer was constructed and used to measure a product line of these pressure swirl atomizers – the macrospray atomizer. This new test stand, utilizing constant temperature hot wire anemometers, captures the spray angle data based on the voltage drop the hot wire probes see as they traverse the spray cone of the atomizer and as fluid droplets impinge upon the wire. Datasets acquired from the experiments are compared and correlated with computational fluid dynamics (CFD) simulation data. In addition, angles obtained from another type of spray characterization technique, the spray angle device, are also compared to see how closely CFD can predict the angle as captured by this new stand and how reliable and independent of human error it is. Another nozzle with a pressure swirl atomizer, the conventional atomizer, is also simulated to compare its agreement with experimental values obtained from the spray angle device. Finally, the datasets are compared to understand if the CFD results, when compared to the two spray characterization techniques used in this thesis for both the nozzle and atomizer can be utilized to assist in future atomizer designs. For the macrospray atomizer, it was found through the experiments that the hot wire stand predicts the spray angle more accurately within 10% error. The spray angle device measured the spray angles within an error of 29% while the CFD introduced more error into the spray angle measurement obtained, within 7% to 93%. The conventional atomizer was found to have an error up to 18% with CFD results and up to 28% with the manual spray angle device.

Committee:

Mounir Ibrahim, Ph.D. (Committee Chair); Vikram Shyam, Ph.D. (Committee Member); Ralph Volino, Ph.D. (Committee Member)

Subjects:

Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

atomization; spray; angles; hot wire anemometry; CFD; simulation; computational fluid dynamics; atomizers; atomizer; pressure swirl atomizer; spray cone; spray; nozzle; nozzles; sprays; measurement; spray angle; cone; air core; hot wire anemometers;

Hylton, Sonya LynnNumerical Investigation of Boiling in a Sealed Tank in Microgravity
Master of Science in Mechanical Engineering, Cleveland State University, 2014, Washkewicz College of Engineering
NASA’s missions in space depend on the storage of cryogenic fluids for fuel and for life support. During long-term storage, heat can leak into the cryogenic fluid tanks. Heat leaks can cause evaporation of the liquid, which pressurizes the tank. However, when the tanks are in a microgravity environment, with reduced natural convection, heat leaks can also create superheated regions in the liquid. This may lead to boiling, resulting in much greater pressure rises than evaporation at the interface between the liquid and vapor phases. Models for predicting the pressure rise are needed to aid in developing methods to control the pressure rise, so that the safety of the storage tank is ensured for microgravity operations. In this work, a CFD model for predicting the pressure rise in a tank due to boiling has been developed and validated against experimental data. The tank was modeled as 2D axisymmetric. The Volume of Fluid (VOF) model in ANSYS Fluent version 15 was modified using a User Defined Function (UDF) to calculate mass transfer between the liquid and vapor phases. A kinetic based Schrage equation was used to calculate the mass flux for evaporation and condensation at the interface. The Schrage equation and the Lee model were compared for calculating the evaporation due to boiling that occurred in the bulk liquid. The results of this model were validated against microgravity data provided by the Tank Pressure Control Experiment, a tank pressurization and pressure control experiment performed aboard the Space Shuttle Mission STS-52 that experienced boiling. During this experiment, the tank pressure rose from about 43400 Pa to about 47200Pa, a difference of about 3800 Pa. The heater temperature rose from about 296K to about 303K, a difference of about 7K. The tank pressure predicted by the CFD model compared well with the experimental pressure data for self-pressurization and boiling in the tank. The validated CFD model uses the Schrage equation to calculate the mass transfer. Three different accommodation coefficients were used, one for evaporation at the interface, one for condensation at the interface, and one for boiling in the bulk liquid. The implicit VOF model with bounded second order time discretization was used.

Committee:

Mounir Ibrahim, PhD (Advisor); Mohammad Kassemi, PhD (Committee Member); Olga Kartuzova, PhD (Committee Member)

Subjects:

Fluid Dynamics; Mechanical Engineering

Keywords:

CFD; Computational Fluid Dynamics; model; boiling; pressure rise; microgravity; tank; engineering; modeling;

Park, Stephen YModeling and Experimental Study of an Open Channel Raceway System to Improve the Performance of Nannochloropsis salina Cultivation
Doctor of Philosophy, The Ohio State University, 2014, Food, Agricultural and Biological Engineering
Lipid-rich microalgae are a potentially favorable alternative source of liquid fuels, and the use of open channel raceways has been proposed as a potential method for their mass cultivation. Studies on energy return on investment (EROI) show that open pond raceways are not feasible enough to be commercialized, but can be considered as a future commodity if energy can be recovered from both lipids and biomass residue. Analyses also show that the energy input in the form of CO2, nutrients, and mixing account for approximately 85% of the total energy consumption for algal biofuel production. Therefore, the conceptual framework of this study was mainly focused on the improvement of the open pond cultivation of the photosynthetic microalgae, Nannochloropsis salina, to increase the EROI of the process. The preexisting open pond cultivation process was hypothesized to be procedurally improved through modifications such as the conversion of algae biomass residue (ABR) via anaerobic digestion (AD) and the addition of phase-change material (PCM) to the open pond surface. A numerical approach was also employed by modeling the demonstration-scale cultivation systems using computational fluid dynamics (CFD) integrated with a kinetic model. The growth kinetics of N. salina was integrated into a 3-dimensional CFD model. Validation in a 120-m3 open channel raceway showed a good fit for the change in biomass, CO2, and nitrogen concentrations. The model also showed the characteristics of dead zones that tail off the bends and increase in biomass concentration. The light attenuation, which is dependent on pond depth and cell concentration, was also observed to drastically increase in the system as the biomass concentration increased. Sensitivity analysis showed that the model was particularly sensitive to the several species-specific parameters. In an attempt to improve the low biomass productivity in the open channel raceways, supposedly caused by excessive water evaporation, susceptibility to contamination, and sensitivity to ambient influences, hexadecane was introduced as a phase change material (PCM) to cover the pond surface. The existing model was modified to accommodate an immiscible secondary phase that flowed in conjunction with the pond medium. Simulated results were compared with the 150-d data acquisition of light intensity, temperature, nutrient concentration, and algal biomass acquired from a demonstration scale raceway pond constructed for the growth of N. salina and were observed to be in good agreement with one another. Additional energy can be generated from ABR by means of anaerobic digestion (AD), but is inhibited by the byproducts of excessive protein degradation. Fat, oil, and grease waste (FOG) from a local municipal waste receiving facility was co-digested with ABR to evaluate the effects on methane yield and degradation of carbohydrates, lipids, and proteins. Co-digestion of ABR and FOG allowed for an increased loading rate while increasing methane yield. Lipids were the key contributor to methane yields. The above results suggest that the production of N. salina in an open environment was substantially improved through the modeling and experimental studies. The knowledge gained from this study may serve as a valuable resource in understanding the issues in the scale up of algal biofuel production and may be applied to other fuel feedstock candidates.

Committee:

Yebo Li (Advisor); Jiyoung Lee (Committee Member); Jay Martin (Committee Member)

Subjects:

Agricultural Engineering; Alternative Energy

Keywords:

Microalgae; computational fluid dynamics; open channel; raceway; modeling; anaerobic digestion; EROI

Fang, Kuan-ChiehUnsteady Incompressible Flow Analysis Using C-Type Grid with a Curved Branch Cut
PhD, University of Cincinnati, 2000, Engineering : Aerospace Engineering
For an unsteady viscous flow simulation on a two-dimensional body at high angle of attack, the calculation of unsteady aerodynamic forces acting on the body is influenced not only by the unsteady separated flow near the body but also by the unsteady wake behind the body. To resolve the wake flow behind the trailing edge, an orthogonal C-grid topology with a curved branch cut aligned with the inviscid stagnation streamline is generated using a conformal mapping technique. This permits the desired grid clustering in the wake region and leads to better flow results in that region. The conformal mapping technique also provides analytical Jacobian metrics for the coordinate transformation and an inviscid solution which is useful in initiating the viscous flow of the impulsively started motion. The use of analytical metric coefficients facilitates the direct determination of part of the coefficients in the governing equations without introducing numerical errors. The unsteady two-dimensional incompressible Navier-Stokes equations in generalized orthogonal coordinates are solved using a vorticity-stream function formulation. The analysis also requires coupling of flow circulation in the far field. As a result, the vorticity-stream function formulation introduced in the present study contains the spatially elliptic equation for the disturbance stream function coupled with the temporally parabolic vorticity transport equation. An efficient direct Block-Gaussian Elimination (BGE) technique is used to solve the stream function Poisson problem subject to Neumann and Dirichlet boundary conditions. The vorticity transport equation is solved using the Alternating Direct Implicit (ADI) method. In addition, the Jacobian at the grid points along the curved branch cut is multi-valued and the metric coefficients are found to be discontinuous across the branch cut. Hence, a special finite element interpolation is implemented in the governing equations at those points in order to overcome this discontinuity. To achieve the objective stated above, the unsteady flow over a stationary NACA 0015 airfoil at various angles of attack is selected in the present study.

Committee:

Kirti Ghia (Advisor)

Keywords:

Computational Fluid Dynamics; Grid Generation

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