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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

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;

Rinehart, Aidan WalkerA Characterization of Seal Whisker Morphology and the Effects of Angle of Incidence on Wake Structure
Master of Science in Mechanical Engineering, Cleveland State University, 2016, Washkewicz College of Engineering
Seal whiskers have been found to produce unique wake flow structures that minimize self-induced vibration and reduce drag. The cause of these wake features are due to the peculiar three-dimensional morphology of the whisker surface. The whisker morphology can be described as an elliptical cross section with variation of diameter in the major and minor axis along the length and, angle of incidence, rotation of the elliptical plane with respect to the whisker axis, α at the peak and β at the trough. This research provided a more complete morphology characterization accomplished through CT scanning and analysis of 27 harbor and elephant seal whisker samples. The results of this study confirmed previously reported values and added a characterization of the angle of incidence finding that the majority of angles observed fall within ±5° and exhibit a random variation in magnitude and direction along the whisker length. While the wake effects of several parameters of the whisker morphology have been studied, the effect of the angle of incidence has not been well understood. This research examined the influence of the angle of incidence on the wake flow structure through series of water channel studies. Four models of whisker-like geometries based on the morphology study were tested which isolate the angle of incidence as the only variation between models. The model variations in angle of incidence selected provided a baseline case (α = β = 0°), captured the range of angles observed in nature (α = β = -5°, and α = β = -15°), and investigated the influence of direction of angle of incidence (α = -5°, β = -5°). The wake structure for each seal whisker model was measured through particle image velocimetry (PIV). Angle of incidence was found to influence the wake structure through reorganization of velocity field patterns, reduction of recovery length and modification of magnitude of Tu. The results of this research helped provide a more complete understanding of the seal whisker morphology relationship to wake structure and can provide insight into design practices for application of whisker-like geometry to various engineering problems.

Committee:

Wei Zhang, PhD (Advisor); Ibrahim Mounir, PhD (Committee Member); Shyam Vikram, PhD (Committee Member)

Subjects:

Aerospace Engineering; Aquatic Sciences; Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

seal; whisker; PIV; biomimicry; fluid dynamics; particle image velocimetry; bio-engineering; engineering; mechanical engineering; aerospace engineering; experimental fluid dynamics;

Jamali, SafaRheology of Colloidal Suspensions: A Computational Study
Doctor of Philosophy, Case Western Reserve University, 2015, Macromolecular Science and Engineering
Computational studies have emerged as a key class of scientific approached to solving different problems of interest in the past few decades. Dissipative Particle Dynamics, DPD, a mesoscale simulation technique based on Molecular Dynamics has been established as a powerful technique in recovering a wide range of physical and chemical processes. Nevertheless, absence of robust bridge between the computational parameters to the physical characteristics of a system has limited applications of DPD. Thus in the second chapter of this dissertation (after a brief introduction and organizational guideline in chapter 1) a systematic study will be presented, providing several routes for setting the simulation parameters based on the real experimental measures. Although computational and theoretical works have always been a crucial areas of research in the rheology society, DPD has not been employed in rheological studies. This is mainly due to the fact that a step-by-step guideline does not exist for rheological measurements in DPD. Another reason for this lack of success in rheological community is that the built-in thermostat in DPD is not capable of providing a stable control over the thermodynamics of the system under flow conditions. Thus, firstly in chapter 3 different methods of viscosity measurement and rheological studies will be discussed in detail, and consequently in chapter 4 a novel thermostat is presented to modify the natural shortcomings of DPD under flow. For decades now, scientists across different disciplines have attempted at identifying the nature of versatile rheological response of colloidal suspensions. Exhibiting Newtonian behavior at very low, shear-thinning at intermediate, and shear-thickening at high flow rates in dense colloidal suspensions exemplifies a broad range of rheological regimes within a simple solid-liquid system. Despite numerous experimental and computational efforts in explaining the underlying mechanism of these behavior, there is still an ongoing debate in the scientific community on the subject. Hence, in final chapter a comprehensive study on rheology of colloidal suspensions (including a complete flow curve, normal stress measurements and microstructural evolutions) is presented, based on the results and foundations in prior chapters as well as in the literature.

Committee:

Joao Maia (Advisor); Wnek Gary (Committee Member); Daniel Lacks (Committee Member); Michael Hore (Committee Member)

Subjects:

Chemical Engineering; Mechanical Engineering; Physics; Polymers

Keywords:

Fluid Dynamics, Rheology, Colloidal Suspensions, Mesoscale Simulations, Dissipative Particle Dynamics, Computational Fluid Dynamics

Thurow, Brian SOn the convective velocity of large-scale structures in compressible axisymmetric jets
Doctor of Philosophy, The Ohio State University, 2005, Mechanical Engineering
The role of compressibility on the convective velocity of large-scale structures in axisymmetric jets is studied using a home-built pulse burst laser system and newly developed high-repetition rate experimental diagnostics. A pulse burst laser system was designed and constructed with the ability to produce a burst of short duration (10 nsec), high energy (order of 10 -100 mJ/pulse) pulses over a ~150 microsecond period with inter-pulse timing as low as 1 microsecond (1 MHz). The application of the pulse burst laser for flow measurements was investigated through the development of MHz rate flow visualization and MHz rate planar Doppler velocimetry (PDV). MHz rate PDV is a spectroscopic technique that produces 28 time-correlated realizations of the velocity over a plane with a maximum repetition rate of up to 1 MHz and accuracies on the order of 5%. Space-time correlations were used to track structures within the flow field and determine their convective velocity. Data produced using flow visualization images agrees with previous research and indicates a strong departure of the convective velocity from theory. Data produced using velocity data, however, shows starkly different trends and does not produce the same measurements of convective velocity. This difference in measurement is attributed to a misinterpretation of the use of space-time correlation for tracking structures. The presence of a distinct boundary between the mixing layer and the jet core as well as the mixing layer and ambient air in the flow visualization data and some of the velocity data leads to a bias in the measurement. The space-time correlation is found to preferentially follow these boundaries, thus leading to faster and/or slower measurements of convective velocity. For the Mach 2.0 jet, velocity data was obtained with seed particles marking the jet core and the mixing layer, but not the ambient air. This lack of velocity measurements on the low-speed side of the jet’s mixing layer biased the space-time correlation results. An algorithm was developed to extrapolate the velocity into unseeded regions of the flow. Space-time correlation results based on the extrapolated data indicate a convective velocity close to the theoretical value.

Committee:

Mo Samimy (Advisor)

Keywords:

compressibility; compressible free shear layers; experimental fluid mechanics; fluid dynamics; aerodynamic measurement techniques; lasers; high-repetition rate lasers; advanced optical diagnostics; compressible fluid dynamics

Bourke, Jason MichaelImplications of Airflow Dynamics and Soft-Tissue Reconstructions for the Heat Exchange Potential of Dinosaur Nasal Passages
Doctor of Philosophy (PhD), Ohio University, 2015, Biological Sciences (Arts and Sciences)
This study seeks to restore the internal anatomy within the nasal passages of dinosaurs via the use of comparative anatomical methods along with computational fluid dynamic simulations. Nasal airway descriptions and airflow simulations are described for extant birds, crocodylians, and lizards. These descriptions served as a baseline for airflow within the nasal passages of diapsids. The presence of shared airflow and soft-tissue properties found in the nasal passages of extant diapsids, were used to restore soft tissues within the airways of dinosaurs under the assumption that biologically unfeasible airflow patterns (e.g., lack of air movement in olfactory recess) can serve as signals for missing soft tissues. This methodology was tested on several dinosaur taxa. Restored airways in some taxa revealed the potential presence and likely shape of nasal turbinates. Heat transfer efficiency was tested in two dinosaur species with elaborated nasal passages. Results of that analysis revealed that dinosaur noses were efficient heat exchangers that likely played an integral role in maintaining cephalic thermoregulation. Brain cooling via nasal expansion appears to have been necessary for dinosaurs to have achieved their immense body sizes without overheating their brains.

Committee:

Lawrence Witmer, PhD (Advisor)

Subjects:

Anatomy and Physiology; Animal Sciences; Biology; Biomechanics; Fluid Dynamics; Paleontology; Scientific Imaging; Zoology

Keywords:

dinosaurs; computational fluid dynamics; CFD; anatomy; reptiles; birds; biomechanics; turbinates; brain cooling; thermoregulation; fluid dynamics; Stegoceras; Euoplocephalus; Panoplosaurus; bony-bounded; airway; nasal passage; nasal cavity

Wukie, Nathan AAn analysis of booster tone noise using a time-linearized Navier-Stokes solver
MS, University of Cincinnati, 2016, Engineering and Applied Science: Aerospace Engineering
This thesis details a computational investigation of tone noise generated from a booster(low-pressure compressor) in a fan test rig. The computational study consisted of sets of time-linearized Navier-Stokes simulations in the booster region to investigate the blade-wake interactions that act as the primary noise-generating mechanism for the booster blade-passing frequency and harmonics. An acoustic test database existed with data at several operating points for the fan test rig that was used to compare against the predicted noise data from the computational study. It is shown that the computational methodology is able to capture trends in sound power for the 1st and 2nd booster tones along the operating line for the rig. It is also shown that the computational study underpredicts one of the tones at low power and is not able to capture a peak in the data at the Cutback condition. Further investigation of this type is warranted to quantify the source of discrepancies between the computational and experimental data as the reflected transmisison of sound off the fan through the bypass duct was not accounted for in this study.

Committee:

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

Subjects:

Aerospace Materials

Keywords:

Computational Aeroacoustics;Turbomachinery;Computational Fluid Dynamics;Acoustics;Frequency-Domain Solvers

Clark, Kylen D.A Numerical Comparison of Symmetric and Asymmetric Supersonic Wind Tunnels
MS, University of Cincinnati, 2015, Engineering and Applied Science: Aerospace Engineering
Supersonic wind tunnels are a vital aspect to the aerospace industry. Both the design and testing processes of different aerospace components often include and depend upon utilization of supersonic test facilities. Engine inlets, wing shapes, and body aerodynamics, to name a few, are aspects of aircraft that are frequently subjected to supersonic conditions in use, and thus often require supersonic wind tunnel testing. There is a need for reliable and repeatable supersonic test facilities in order to help create these vital components. The option of building and using asymmetric supersonic converging-diverging nozzles may be appealing due in part to lower construction costs. There is a need, however, to investigate the differences, if any, in the flow characteristics and performance of asymmetric type supersonic wind tunnels in comparison to symmetric due to the fact that asymmetric configurations of CD nozzle are not as common. A computational fluid dynamics (CFD) study has been conducted on an existing University of Michigan (UM) asymmetric supersonic wind tunnel geometry in order to study the effects of asymmetry on supersonic wind tunnel performance. Simulations were made on both the existing asymmetrical tunnel geometry and two axisymmetric reflections (of differing aspect ratio) of that original tunnel geometry. The Reynolds Averaged Navier Stokes equations are solved via NASA’s OVERFLOW code to model flow through these configurations. In this way, information has been gleaned on the effects of asymmetry on supersonic wind tunnel performance. Shock boundary layer interactions are paid particular attention since the test section integrity is greatly dependent upon these interactions. Boundary layer and overall flow characteristics are studied. The RANS study presented in this document shows that the UM asymmetric wind tunnel/nozzle configuration is not as well suited to producing uniform test section flow as that of a symmetric configuration, specifically one that has been scaled to have equal aspect ratio. Comparisons of numerous parameters, such as flow angles, pressure (both static and stagnation), entropy, boundary layers and displacement thickness, vorticity, etc. paint a picture that shows the symmetric equal aspect ratio configuration to be decidedly better at producing desirable test section flow. It has been shown that virtually all parameters of interest are both more consistent and have lower deviation from ideal conditions for the symmetric equal area configuration.

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;Wind tunnels;Asymmetric Supersonic Nozzles;Test section flow;flow uniformity;Converging Diverging Nozzles

Miller, Samuel C.Fluid-Structure Interaction of a Variable Camber Compliant Wing
Master of Science (M.S.), University of Dayton, 2015, Aerospace Engineering
This thesis presents results from loosely-coupled fluid-structure interaction (FSI) simulations of a flexible wing which used FUN3D to compute the aerodynamic flow-fields and Abaqus to calculate the structural deformations. NASA Langley also provides a general 3D algorithm to interpolate between dissimilar meshes which is used here to map pressures and displacements between the aerodynamic and structural codes. This method is applied to the AFRL - developed “Variable Camber Compliant Wing” (VCCW), which is an adaptable wing designed to target airfoil shapes between a NACA 2410 and 8410. The VCCW was tested in the Vertical Wind Tunnel facility at Wright-Patterson Air Force Base, which provided experimental data in the form of static pressure tap data, digital image correlation, and oil flow visualization. The combined solutions from Abaqus, FUN3D, and mesh interpolation solvers created FSI results that were similar in trend to the experiment, but consistently under-predicted the deformations of the VCCW, due to the differences between the experiment and simulation, including the choice of material models and the assumption of ideal conditions. This thesis has been cleared by the Wright-Patterson AFB Public Affairs Office, case number 88ABW-2015-1502. This provides proof of public release, distribution unlimited.

Committee:

Markus Rumpfkeil, Phd (Advisor); James Joo, Phd (Committee Member); Jose Camberos, Phd (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

CFD; FSI; Computational Fluid Dynamics; Fluid-Structure Interaction;Flexible Wings; Compliant Mechanism; Loosely-Coupled; FUN3D; Abaqus; Python

Ickes, JacobImproved Helicopter Rotor Performance Prediction through Loose and Tight CFD/CSD Coupling
Master of Science, University of Toledo, 2014, Mechanical Engineering
Helicopters and other Vertical Take-Off or Landing (VTOL) vehicles exhibit an interesting combination of structural dynamic and aerodynamic phenomena which together drive the rotor performance. The combination of factors involved make simulating the rotor a challenging and multidisciplinary effort, and one which is still an active area of interest in the industry because of the money and time it could save during design. Modern tools allow the prediction of rotorcraft physics from first principles. Analysis of the rotor system with this level of accuracy provides the understanding necessary to improve its performance. There has historically been a divide between the comprehensive codes which perform aeroelastic rotor simulations using simplified aerodynamic models, and the very computationally intensive Navier-Stokes Computational Fluid Dynamics (CFD) solvers. As computer resources become more available, efforts have been made to replace the simplified aerodynamics of the comprehensive codes with the more accurate results from a CFD code. The objective of this work is to perform aeroelastic rotorcraft analysis using first-principles simulations for both fluids and structural predictions using tools available at the University of Toledo. Two separate codes are coupled together in both loose coupling (data exchange on a periodic interval) and tight coupling (data exchange each time step) schemes. To allow the coupling to be carried out in a reliable and efficient way, a Fluid-Structure Interaction code was developed which automatically performs primary functions of loose and tight coupling procedures. Flow phenomena such as transonics, dynamic stall, locally reversed flow on a blade, and Blade-Vortex Interaction (BVI) were simulated in this work. Results of the analysis show aerodynamic load improvement due to the inclusion of the CFD-based airloads in the structural dynamics analysis of the Computational Structural Dynamics (CSD) code. Improvements came in the form of improved peak/trough magnitude prediction, better phase prediction of these locations, and a predicted signal with a frequency content more like the flight test data than the CSD code acting alone. Additionally, a tight coupling analysis was performed as a demonstration of the capability and unique aspects of such an analysis. This work shows that away from the center of the flight envelope, the aerodynamic modeling of the CSD code can be replaced with a more accurate set of predictions from a CFD code with an improvement in the aerodynamic results. The better predictions come at substantially increased computational costs between 1,000 and 10,000 processor-hours.

Committee:

Chunhua Sheng, Ph.D. (Advisor); Abdeh Afjeh, Ph.D. (Committee Member); Ray Hixon, Ph.D. (Committee Member); Glenn Lipscomb, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

Computational Fluid Dynamics; Computational Structural Dynamics; CFD; CSD; Helicopter; Rotor; Coupling; UH-60A; Rotorcraft; Aerodynamics

Byrd, Alex W.Fluid-Structure Interaction Simulations of a Flapping Wing Micro Air Vehicle
Master of Science in Engineering (MSEgr), Wright State University, 2014, Mechanical Engineering
Interest in micro air vehicles (MAVs) for reconnaissance and surveillance has grown steadily in the last decade. Prototypes are being developed and built with a variety of capabilities, such as the ability to hover and glide. However, the design of these vehicles is hindered by the lack of understanding of the underlying physics; therefore, the design process for MAVs has relied mostly on trial-and-error based production. Fluid-Structure Interaction (FSI) techniques can be used to improve upon the results found in traditional computational fluid dynamics (CFD) simulations. In this thesis, a verification of FSI is first completed, followed by FSI MAV simulations looking at different prescribed amplitudes and flapping frequencies. Finally, a qualitative comparison is made to high speed footage of an MAV. While the results show there are still model improvements that can be made, this thesis hopes to be a stepping stone for future analyses for FSI MAV simulations.

Committee:

George Huang, Ph.D. (Advisor); Philip Beran, Ph.D. (Committee Member); Joseph Shang, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

Micro air vehicles; Fluid Structure Interaction; Computational Fluid Dynamics; MAV; FSI; CFD

Cuppoletti, Daniel RSupersonic Jet Noise Reduction with Novel Fluidic Injection Techniques
PhD, University of Cincinnati, 2013, Engineering and Applied Science: Aerospace Engineering
Supersonic jets provide unique challenges in the aeroacoustic field due to very high jet velocities, shock associated noise components, flow dependence on jet expansion, and stringent performance requirements. Current noise suppression technology for commercial and military jet engines revolves around using chevrons or mechanical vortex generators to increase mixing near the nozzle exit, subsequently reducing peak turbulence levels in the mixing region. Passive noise control methods such as mechanical chevrons cause thrust loss throughout the flight envelope and performance can vary with the engine operating condition. Development of active noise control methods have the potential of improved performance throughout the flight envelope and the benefit of being deactivated when noise control is unnecessary. Fluidic injection of air into a supersonic jet is studied as an active control method with an emphasis on understanding the physics of the problem and identifying the controlling parameters. An experimental investigation with computational collaboration was conducted to understand the effect of nozzle design on supersonic jet noise and to develop various fluidic injection techniques to control noise from a supersonic jet with a design Mach number of 1.56. The jet was studied at overexpanded, ideally expanded, and underexpanded conditions to evaluate the effects throughout the operational envelope. As a passive noise control method, the internal contour of a realistic nozzle was modified to investigate the effect on acoustics and performance. Thrust was improved up to 10% with no acoustic penalties through nozzle design, however it was found that the shock noise components were highly sensitive to the shock structure in the jet. Steady fluidic injection was used to generate vorticity at the trailing edge of the nozzle showing that noise reduction is achieved through vorticity generation, modification of the shock structure, and interference with the screech feedback mechanism by decoupling the phase relationship between jet turbulence and shock spacing. Reduction of shock noise was found to be optimum at an intermediate injection pressure due to shock weakening from the fluidic injectors and injector interactions with the jet shock-expansion structure. Large-scale mixing noise reduction was shown to depend on the vorticity strength and circulation. Unprecedented reduction of OASPL up to -8.5 dB were achieved at the peak noise direction through strong jet mixing and rapid collapse of the potential core. Pulsed fluidic injection was investigated to understand the acoustic benefits and drawbacks of unsteady injection. Valve frequency response up to 500 Hz was achieved but noise reduction dropped off above 100 Hz due to poor flow response as verified by hot-wire and dynamic pressure measurements. At low pulse frequencies it was found that moderate noise reduction could be achieved with less flow than steady injection, but in general the mixing noise reduction scaled with the time integrated mass flow injection. It was discovered that the different components of supersonic jet noise had different characteristic response times to unsteady injection. Analysis of high speed shadowgraph images and acoustic spectra was used to identify time response of the jet during the unsteady injection cycle.

Committee:

Ephraim Gutmark, Ph.D., D.Sc. (Committee Chair); Steve Martens, Ph.D. (Committee Member); Awatef Hamed, Ph.D. (Committee Member); Jeffrey Kastner, Ph.D. (Committee Member); David Munday, Ph.D. (Committee Member); Mark Turner, Sc.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Jet Noise;Aeroacoustics;Fluid Dynamics;Particle Image Velocimetry;Acoustics;Supersonic

Doucet, Daniel JosephMeasurements of Air Flow Velocities in Microchannels Using Particle Image Velocimetry
Master of Sciences (Engineering), Case Western Reserve University, 2012, EMC - Aerospace Engineering
The knowledge of the flow field in microchannels is becoming increasingly important with the advent of the ionic wind pump and other microscale heat removal devices. The understanding of this flow field will lead to more effective and improved designs. Non-intrusive microscale particle image velocimetry (PIV) utilizing a microscopic objective lens is used to obtain the velocity field in microchannels. The scales of these channels are similar to those encountered in such devices as the ionic wind pump. Microchannels with dimensions ranging from 0.8 mm to 2 mm are used. Computational fluid dynamics (CFD) models are used to replicate each test, with varying inlet conditions and mesh densities. The CFD flow fields are compared to the PIV results for validation purposes, with relative errors between CFD and PIV typically between 2% and 10%. The agreement between the experimental data and computational results ranged from acceptable to excellent, validating this method. The channel with lowest aspect ratio consistently showed the largest agreement between experimental and numerical values.

Committee:

Jaikrishnan R. Kadambi, PhD (Advisor); J. Iwan D. Alexander, PhD (Committee Member); Vikas Prakash, PhD (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

particle image velocimetry; computational fluid dynamics; microchannel; experimental fluid mechanics

Fife, Jane PattersonInvestigation of the effect of agricultural spray application equipment on damage to entomopathogenic nematodes - a biological pest control agent
Doctor of Philosophy, The Ohio State University, 2003, Food, Agricultural, and Biological Engineering
Biological pesticides (i.e., biopesticides) are living systems, which introduce additional challenges with respect to formulation and delivery not previously encountered with conventional chemical pesticides. Understanding the effects of the different physical phenomena within a spray system is important to begin identifying the equipment characteristics and operating conditions that are least detrimental to the biological agents. Specifically, this work considered the effects of pressure differentials and hydrodynamic stress on damage to a benchmark biological pest control agent, entomopathogenic nematodes (EPNs). Four EPN species were evaluated in this work: Heterorhabditis bacteriophora, H. megidis, Steinernema carpocapsae, and S. glaseri. Additionally, temperature influences due to pump recirculation were investigated. Results from this work indicate that S. carpocapsae nematodes were able to withstand greater pressure differentials and more intensive hydrodynamic conditions than the other EPN species. Consequently, EPN species is an important factor to consider when defining spray operating conditions. Operating pressures within a spray system should not exceed 2000 kPa (290 psi) for H. bacteriophora and S. carpocasae, and 1380 kPa (200 psi) for H. megidis. Other EPN species may require lower pressure. Experimental results of EPN damage after passage through an abrupt contraction and two common types of hydraulic nozzles (flat fan and cone) were compared to flow parameters from numerical simulations of the experimental flow fields using FLUENT, a commercial computational fluid dynamics (CFD) program. Based on the flow field characteristics, the rotational flow regime within a cone type nozzle produces hydrodynamic conditions that are less damaging to EPNs compared to the extensional flow developed within the narrow, elliptic exit orifice of the flat fan nozzle. It was found that the tensile stress loading that occurs during flow into a constricted region, which characterizes an extensional flow, is damaging to the biological material. An empirical model comparing average energy dissipation rates computed in FLUENT to observed EPN damage was developed. Overall, the model was able to predict the EPN damage after treatment with the hydraulic nozzles well, in many cases within 5%. These results show that CFD is a feasible method to evaluate the flow conditions within an equipment component to assess its compatibility with a biological agent. Finally, extensive recirculation of the tank mix can cause considerable increases in the liquid temperature. It was found that either a diaphragm or roller pump is better suited for use with biopesticides, compared to a high-capacity centrifugal pump, which contributes significant heat to the spray system.

Committee:

H. Ozkan (Advisor)

Keywords:

entomopathogenic nematodes; spray application equipment; hydraulic nozzles; pressure differential; hydrodynamic stress; damage; computational fluid dynamics; energy dissipation rate; pump recirculation; temperature

Morris, Seth HendersonQuasi-Transient Calculation of Surface Temperatures on a Reusable Booster System with High Angles of Attack
Master of Science (M.S.), University of Dayton, 2011, Aerospace Engineering
The calculation of a recovery temperature based heat transfer coefficient proves to be sufficiently independent of wall temperature to use in a three dimensional, transient temperature model of a thermal protection system of a reusable booster concept. After a derivation of recovery temperature from the 1st law of thermodynamics, the weak dependence of the recovery temperature based heat transfer coefficient is investigated by 72 Computational Fluid Dynamics (CFD) models at angles of attack ranging from 0° to 90° over a range of Mach numbers, from Mach 2 to 5, and a variety of thermal boundary conditions at the wall, from isothermal to a conductive wall. Then, the heat transfer coefficient is calculated at many steady state CFD solutions for a reusable booster system concept on a given trajectory and applied to a transient Finite Element Analysis (FEA) model of a thermal protection system. Results are presented graphically.

Committee:

Timothy J. Fry, PhD (Committee Chair); José A. Camberos, PhD, PE (Committee Member); John Doty, PhD (Committee Member)

Subjects:

Aerospace Engineering; Atmosphere; Computer Science; Fluid Dynamics; High Temperature Physics; Mechanical Engineering

Keywords:

quasi; transient; heat; transfer; coefficient; hypersonic; CFD; computational; fluid; dynamics; thermodynamic; FEA; steady; state; recovery; temperature; reusable; booster; system; high; speed; computing; super; computer; kinetic; energy

Yu, YangA Numerical Approach for Interfacial Motion and its Application to viscous effects in the Benjamin-Feir instability
Doctor of Philosophy, The Ohio State University, 2009, Mathematics

The evolution of the free interface between two incompressible viscous fluid flows occurs in many physical problems. The numerical simulation of these free surfaces presents great difficulties in scientific computing, especially when the Reynolds number is very large.

In this thesis, a new numerical approach is introduced to simulate the two-dimensional viscous incompressible fluid flows with free interface. A mapped coordinate system is used to transform the curved geometry into a rectangular region so that a standard grid can be applied to the region. The Navier-Stocks equations using the stream function and vorticity are solved together with the interface conditions between two fluids. The second-order backward difference formula is used for time evolution. An implicit/explicit method is used to avoid iterative procedure when handling the nonlinear terms. A periodic boundary condition is assumed in the horizontal direction and spectral methods are applied. The equations are then written as a first order ODE system in the vertical direction. In order to achieve a stable numerical method for calculations with huge Reynolds number as well as a high accuracy, a forth-order boundary value problem solver is introduced to solve this ODE system. In order to get the initial conditions for the simulation, linear stability analysis with the interface is performed within the mapped geometry. The non-linear parts of the system are input into the simulation gradually in order to get a smooth transformation from the linear initial condition to the non-linear simulation.

As an important application of this new method, the viscous effects on the Benjamin-Feir Instability for the deep water wave are studied. The simulation results show that the viscosity has a strong impact on the development of the Benjamin-Feir instability. For waves of small wavelength where viscous effects are mere pronounced, the Benjamin-Feir instability will be suppressed by the viscous damping after a certain amount of time.

Committee:

Gregory Baker (Advisor); Edward Overman (Committee Member); Chiu-Yan Kao (Committee Member)

Subjects:

Mathematics

Keywords:

Computational fluid dynamics; numerical analysis; interface motion;

Dibling, David R.Development And Validation Of A High-Resolution, Nearshore Model For Lake Erie
Master of Science, The Ohio State University, 2012, Civil Engineering
The purpose of this research is to make progress toward correcting the nearshore deficiency of the current hydrodynamic model used by Lake Erie by developing and validating a state-of-the-art hydrodynamic and transport model infrastructure capable of highly accurate simulations in the nearshore zone. This was accomplished by creating a high-resolution mesh using high-resolution GPS images to create an up-to-date shoreline. The bathymetry was then used to determine where more resolution was needed in order to capture the water movement using an unstructured mesh (10 meter resolution) rather than the old structured mesh (5 km resolution) that did not accurately represent the shoreline. Simulations were run using the ADCIRC-SWAN (ADvanced CIRCulation Simulating WAves Nearshore) model on the new mesh and the results are presented. This model passed a required NOS (National Ocean Service) skills assessment in order for the hindcast model to be validated.

Committee:

Ethan J. Kubatko, PhD (Advisor); Gil Bohrer, PhD (Committee Member); Gajan Sivandran, PhD (Committee Member)

Subjects:

Civil Engineering; Computer Engineering; Environmental Engineering; Fluid Dynamics

Keywords:

Lake Erie; ADCIRC; SWAN; hydrodynamic model; hindcast; finite element; fluid dynamics

Marks, Christopher R.Surface Stress Sensors for Closed Loop Low Reynolds Number Separation Control
Doctor of Philosophy (PhD), Wright State University, 2011, Engineering PhD
Low Reynolds number boundary layer separation causes reduced aerodynamic performance in a variety of applications such as MAVs, UAVs, and turbomachinery. The inclusion of a boundary layer separation control system offers a way to improve efficiency in conditions that would otherwise result in poor performance. Many effective passive and active boundary layer control methods exist. Active methods offer the ability to turn on, off, or adjust parameters of the flow control system with either an open loop or closed loop control strategy using sensors. This research investigates the use of a unique sensor called Surface Stress Sensitive Film (S3F) in a closed loop, low Reynolds number separation control system. S3F is an elastic film that responds to flow pressure gradients and shear stress along its wetted surface, allowing optical measurement of wall pressure and skin friction. A new method for installing the S3F sensor to assure a smooth interface between the wall and wetted S3F surface was investigated using Particle Image Velocimetry techniques (PIV). A Dielectric Barrier Discharge (DBD) plasma actuator is used to control laminar boundary layer separation on an Eppler 387 airfoil over a range of low Reynolds numbers. Several different DBD plasma actuator electrode configurations were fabricated and characterized in an open loop configuration to verify separation control of the Eppler 387 boundary layer. The open loop study led to the choice of a spanwise array of steady linear vertical jets generated by DBD plasma as the control system flow effecter. Operation of the plasma actuator resulted in a 33% reduction in section drag coefficient and reattachment of an otherwise separated boundary layer. The dissertation culminates with an experimental demonstration of S3F technology integrated with a control system and flow effecter for closed loop, low Reynolds number separation control. A simple On/Off controller and Proportional Integral (PI) controller were used to close the control loop.

Committee:

Mitch Wolff, PhD (Advisor); Rolf Sondergaard, PhD (Committee Member); James Menart, PhD (Committee Member); Mark Reeder, PhD (Committee Member); Joseph Shang, PhD (Committee Member)

Subjects:

Aerospace Engineering; Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

low Reynolds number; fluid dynamics; surface stress sensitive film; flow control; separation control; S3F; plasma actuator; dielectric barrier discharge;

Hug, Scott A.Computational Fluid Dynamics Modeling of a Gravity Settler for Algae Dewatering
Master of Science in Chemical Engineering, Cleveland State University, 2013, Fenn College of Engineering
Algae are the future of lipid sources for biodiesel production. Algae can produce more biodiesel than soybean and canola oil and can be grown in more diverse locations. Algae concentrations are naturally around 0.1% by weight. Enough water must be removed for the algae level to reach 5%, the minimum concentration in which lipids can be used in the transesterification process for biofuel production is 5%. Current dewatering methods involve the use of settling tanks and centrifugation. The costs of centrifugation limit the commercial viability of algae based biodiesel. A novel inclined gravity settler design at Cleveland State University is analyzed in this project. A major difference between this and a traditional gravity settler is that the inlet of this gravity settler is at the top, whereas traditional gravity settlers have inlets at the bottom. A computational fluid dynamics model for the system has been developed to allow the simulations of fluid flow and particle trajectories over time. These simulations determine the optimal conditions for algae dewatering. Results show that the concentration increase of algae is largely dependent on the settler's angle of inclination, inlet flow rate, and the split ratio of water between the overflow (predominantly water) and underflow (concentrated algae) outlets. A 50-fold concentration increase requires multiple settlers set up in series. A two- or three-settler design is sufficient to increase algae concentration the desired level.

Committee:

Jorge Gatica, PhD (Committee Chair); Joanne Belovich, PhD (Committee Member); Chandra Kothapalli, PhD (Committee Member); Dhananjai Shah, PhD (Committee Member)

Subjects:

Alternative Energy; Chemical Engineering

Keywords:

Algae; Dewatering; Gravity settler; Inclined gravity settler; Fluid dynamics; Fluid flow; Particle trajectories;

Kastner, Jeffrey F.Far-field radiated noise mechanisms in high reynolds number and high-speed jets
Doctor of Philosophy, The Ohio State University, 2007, Mechanical Engineering
The present research examines the relationship between the large-scale structure dynamics of a jet and the far-field sound. This was achieved by exploring the flowfield and the far field of an axisymmetric Mach 0.9 jet with a Reynolds number of approximately 0.76 million. The jet is controlled by eight plasma actuators, which operate over a large frequency range and have independent phase control allowing excitation of azimuthal modes (m) 0, 1, 2, and 3. The jet’s far field is probed with a microphone array positioned at 30 degrees with respect to the downstream jet axis. The array is used to estimate the origin of peak sound events in space, and find the sound pressure level (SPL) and overall sound pressure level (OASPL). The lower forcing Strouhal numbers (StDF’s) increase the OASPL and move noise sources upstream while higher StDF’s decrease the OASPL and have noise source distributions similar to the baseline jet. The flowfield was investigated using particle image velocimetry (PIV). A Reynolds decomposition of the PIV data emphasized the importance of the streamwise velocity fluctuations for the symmetric azimuthal modes (m = 0 and 2) and the cross-stream velocity fluctuations for the asymmetric azimuthal modes (m = 1 and 3). A proper orthogonal decomposition of the PIV data was performed to extract information about how forcing affects the large-scale flow features and conditionally average the PIV data. When forcing at StD’s other than the preferred mode, the conditional-averaged images show large-scale flow features that grow, saturate, and decay closer to the nozzle exit. When exciting a symmetric azimuthal mode, m = 0, near the preferred StDF, the streamwise phase-averaged velocity grows quickly and saturates over a relatively long spatial range. When exciting an asymmetric azimuthal mode, m = 1, near the preferred StDF, the cross-stream phase-averaged velocity grows slowly, saturates, and then decays relatively quickly. The noise source distribution occurred in the decay region for both m = 0 and m = 1, and the distribution changed in accordance with changes in the decay rate.

Committee:

Mo Samimy (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

Fluid Dynamics; Gas Dynamics; Aeroacoustics; Optical Diagnostics

Chang, QingmingLATTICE BOLTZMANN METHOD (LBM) FOR THERMAL MULTIPHASE FLUID DYNAMICS
Doctor of Philosophy, Case Western Reserve University, 2006, Mechanical Engineering
A multiphase lattice Boltzmann method (MLBM) based on the HSD model has been adapted for the solution of multiphase fluid dynamics problem. The interactions between particles are expressed through a mean-field approximation and exclusion-volume effect. The behavior of interface is obtained as part of the solution of the lattice Boltzmann equations. No a priori assumptions and artificial treatment are made regarding the shape and dynamic roles of the interface. Interfacial tension dynamics is validated through a series of test running of three-dimensional wave dispersion. The MLBM is also extended to thermal multiphase LBM (TMLBM) which includes the effects of interfacial tension and its dependence on temperature by a hybrid scheme. The key point for this scheme is combining a micro-scale description of the flow with a macroscopic energy transport equation. Applying the TMLBM, a systematic investigation of fluid dynamics in a two-layer immiscible fluid system is undertaken starting with Rayleigh-Benard convection. A parametric study of the effects of thermally induced density change, buoyancy, surface tension variation with temperature on interface dynamics, flow regimes and heat transfer is presented. Further investigation of TMLBM is applied to a two-layer immiscible fluid system with density inversion in which density inverse assumption holds for the lower layer fluid. The evaluation of the effects of density distribution parameter, Rayleigh number, size aspect ratio and Marangoni number on convection flow and heat transfer is presented. Interaction between gravity-induced and vibration-induced thermal convection in a two-layer fluid system has also be studied by TMLBM. The vibrations considered correspond to sinusoidal translations of a rigid cavity at a fixed frequency and is parallel to temperature gradient. The ability of applied vibration to enhance the flow, heat transfer and interface distortion is investigated. Comparisons of two-phase fluid system with single-phase fluid system are discussed. Finally, a nearest-neighbor molecular interaction force is introduced into LB equation to model the adhesive forces between the fluid and solid surface. The behavior of a micron-scale fluid droplet on a heterogeneous surface is investigated. The dependence of spreading/breakup behavior of a hemispherical droplet on the structure and wettability of the surface and gravity is investigated.

Committee:

J. Iwan D. Alexander (Advisor)

Keywords:

Lattice Boltzmann Method; Multiphase fluid dynamics; Droplet Spreading dynamics; Two-phase Rayleigh-Benard Convection; Thermovibrational Convection; Micro-scale Fluidics

Anderson, Eric JamesBRIDGING THE GAP IN UNDERSTANDING BONE AT MULTIPLE LENGTH SCALES USING FLUID DYNAMICS
Doctor of Philosophy, Case Western Reserve University, 2007, Mechanical Engineering
Fluid flow through the network of pathways in bone tissue is hypothesized to play an integral role in transducing external mechanical forces from the skeletal level down to the cells embedded deep within bone tissue. Communicating these external forces to bone cells is thought to be the mechanism by which bone is regenerated, and thus has major implications in fighting bone disease as well as repairing defects or damage to the tissue. This research pursues the role of fluid flow in bone remodeling and looks to bridge the gap between tissue and cellular level knowledge using computational fluid dynamics modeling of Navier-Stokes equations as well as experimental validations of applicable models. Using physiologic model geometries of increasing complexity, the following work predicts currently immeasurable propeties of this tissue such as permeability or cell communication, as well as the resultant mechanical forces as they exist at the cellular and subcellular levels. The mechanical environment of the osteocyte is described, where the mode and magnitude of force on the cell varies spatio-temporally. Both the hydrodynamic pressure and imparted shear stress are found on the cell surface, where the cell body experiences a nearly constant pressure and virtually zero shear stress while the cell processes are exposed to high gradients of both shear stress and pressure. This differentiation between types and location of forces has possible implications in cell physiology and the types of receptors or mechanosensors present on the cell. In addition, along the cell processes, which radiate from the cell body, subcellular geometries near the lower continuum-limit yield small discontinuities in the annular wall that are foundt o amplify peak shear stresses up to five times that of previous predictions. This result gives insight into a major paradox that has existed in bone and suggests a bridge between theoretical predictions and laboratory measurements of the necessary mechanical force for cell stimulation, where previous in vitro measurements have been an order of magnitude higher than in vivo predictions. This knowledge of the cell's mechanical environment is used to improve and design applications for laboratory cell studies and tissue growth in vitro.

Committee:

Melissa Knothe Tate (Advisor)

Keywords:

mechanotransduction; bone fluid flow; computational fluid dynamics; osteocyte

Ingraham, DanielExternal Verification Analysis: A Code-Independent Approach to Verifying Unsteady Partial Differential Equation Solvers
Doctor of Philosophy, University of Toledo, 2015, Mechanical Engineering
External Verification Analysis (EVA), a new approach to verifying unsteady partial differential equation codes, is presented. After a review of the relevant code verification literature, the mathematical foundation and solution method of the EVA tool is discussed in detail. The implementation of the EVA tool itself is verified through an independent Python program. A procedure for code verification with the EVA tool is described and then applied to the three-dimensional form of a high-order non-linear computational aeroacoustics code.

Committee:

Ray Hixon (Advisor); Sorin Cioc (Committee Member); James DeBonis (Committee Member); Mehdi Pourazady (Committee Member); Chunhua Sheng (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

code verification; computational aeroacoustics; computational fluid dynamics; numerical partial differential equations

Bazow, Dennis P.Fluid dynamics for the anisotropically expanding quark-gluon plasma
Doctor of Philosophy, The Ohio State University, 2017, Physics
Local momentum anisotropies are large in the early stages of the quark-gluon plasma created in relativistic heavy-ion collisions, due to the extreme difference in the initial longitudinal and transverse expansion rates. In such situations, fluid dynamics derived from an expansion around an isotropic local equilibrium state is bound to break down. Instead, we resum the effects of the slowest nonhydrodynamic degree of freedom (associated with the deviation from momentum isotropy) and include it at leading order, defining a local anisotropic quasi-equilibrium state, thereby treating the longitudinal/transverse pressure anisotropy nonperturbatively. Perturbative transport equations are then derived to deal with the remaining residual momentum anisotropies. This procedure yields a complete transient effective theory called viscous anisotropic hydrodynamics. We then show that the anisotropic hydrodynamic approach, especially after perturbative inclusion of all residual viscous terms, dramatically outperforms viscous hydrodynamics in several simplified situations for which exact solutions exist but which share with realistic expansion scenarios the problem of large dissipative currents. Simulations of the full three-dimensional dynamics of the anisotropic quark-gluon plasma are then presented.

Committee:

Ulrich Heinz (Advisor); Michael Lisa (Committee Member); Yuri Kovchegov (Committee Member); Junko Shigemitsu (Committee Member)

Subjects:

Physics

Keywords:

Relativistic fluid dynamics; Quark-gluon plasma; Anisotropic dynamics; Viscous hydrodynamics; Boltzmann equation; GPU; CUDA; Parallel computing

Hama, BrianEvaluation of a Microfluidic Mixer Utilizing Staggered Herringbone Channels: A Computational Fluid Dynamics Approach
Master of Science in Chemical Engineering, Cleveland State University, 2017, Washkewicz College of Engineering
Microfluidic platforms offer a variety of advantages including improved heat transfer, low working volumes, ease of scale-up, and strong user control on parameters. However, flow within microfluidic channels occurs at low Reynolds numbers, which makes mixing difficult to accomplish. Adding V-shaped ridges to channel walls, a pattern called the staggered herringbone design (SHB), might alleviate this problem by introducing transverse flow patterns that enable enhanced mixing. However, certain factors affecting the SHB mixer’s performance remain largely unexplored. In this work, a microfluidic mixer utilizing the SHB geometry was developed and characterized using computational fluid dynamics based simulations and complimentary experiments. A channel design with SHB ridges was simulated in COMSOL Multiphysics under a variety of operating conditions to evaluate its mixing capabilities. The device was fabricated using soft-lithography to experimentally observe the mixing process. The mixing was visualized by pumping fluorescent dyes through the device and imaging the channels using a confocal microscope. The device was found to efficiently mix fluids rapidly, based on both simulations and experiments. Varying the Reynolds number or component diffusion coefficients had a weak effect on the mixing profile, due to the laminar flow regime and insufficient residence time, respectively. Mixing effectiveness decreased as the component flow rate ratio increased. Fluid flow patterns visualized in confocal microscope images were highly identical to the simulated results, suggesting that the simulations serve as good predictors of the device’s performance. This SHB mixer design would be a good candidate for further implementation as a reactor.

Committee:

Chandra Kothapalli, Ph.D. (Committee Chair); Jorge Gatica, Ph.D. (Committee Member); Petru Fodor, Ph.D. (Committee Member); Miron Kaufman, Ph.D. (Committee Member)

Subjects:

Chemical Engineering

Keywords:

microfluidics; mixing; computational fluid dynamics; comsol; staggered herringbone

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