Master of Sciences (Engineering), Case Western Reserve University, 2022, EMC - Aerospace Engineering

Numerical simulations are performed to support a combustion experiment campaign in partial gravity in a centrifuge designed for use in conjunction with the NASA Glenn Research Center's Zero Gravity Research Facility (a 5.2 second drop tower). The centrifuge is a circular dome chamber of volume ~ 0.3 m3 with 81.3 cm diameter. The artificial gravitational field is controlled by the rotation rate of the chamber. This is complicated by gravitational gradients as a function of radius and by Coriolis force as a function of flow velocity. The model is constructed with Ansys FLUENT utilizing a rotating non-inertial reference frame and simulates the entire chamber volume containing a heptane candle with a wick length of 10 mm × 3.18 mm diameter located at 32 cm from the centrifuge center. Simulation results locally near the candle are compared to a series of experiment images where the flame tip bends in the Coriolis force direction. The study investigates the recirculation effects and the relation between the buoyancy and the Coriolis force in how they affect the flame. The model simulates the experiments well and suggestions are made to avoid recirculation effects in future centrifuge experiments.

Committee: Ya-Ting Liao (Committee Chair); Paul Barnhart (Committee Member); Ankit Sharma (Committee Member); Paul Ferkul (Committee Member); Michael Johnston (Committee Member); Bryan Schmidt (Committee Member) Subjects: Aerospace Engineering

Master of Science in Mechanical Engineering (MSME), Wright State University, 2021, Mechanical Engineering

This study characterizes the functional dependence of drag on Reynolds number for a deformed vacuum lighter-than-air vehicle. The commercial computational fluid dynamics (CFD) code, FLUENT, is used to preform large eddy simulations (LES) over a range of Reynolds numbers; only Reynolds numbers less than 310,000 are considered. While the overarching goal is drag characterization, general flow-field physics are also discussed, including basic turbulence spectra. All large eddy simulations are preceded by a Reynolds-averaged Navier-Stokes (RANS) simulation using Menter's shear stress transport (SST) model. The precursor RANS simulation serves to (1) provide realistic initial conditions, (2) decrease the time needed to achieve a statistically averageable state, (3) assess near-wall mesh resolution, and (4) provide an estimate of the integral length scale. After achieving a statistically averageable state, each LES is integrated for at least 5 through-flow times. For sub-grid scale modeling, turbulence kinetic energy (TKE) transport is enabled, as it is the only model which allows for direct assessment of TKE resolution; all simulations resolve at least 80% of the total TKE at every point in the computational domain. To validate this study, all calculated drag coefficients are compared with experimental wind tunnel data.

Committee: Mitch Wolff Ph.D. (Committee Chair); Anthony N. Palazotto Ph.D., P.E. (Committee Co-Chair); George P. Huang Ph.D. (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2021, Aerospace Engineering

Nuclear Thermal Propulsion (NTP) will be an enabling technology for future deep space exploration missions. The high energy density of a nuclear reactor allows for the hydrogen propellant to reach exit velocities much greater than what is possible with traditional chemical propulsion, but that high energy density also presents some issues that must be designed around. Most notably, the decay heat produced after shutdown needs to be removed by venting hydrogen through the core. This thesis attempts to determine the minimum amount of hydrogen propellant that must be spent in this way by computationally modelling a portion of the core to predict exactly what mass flowrate is necessary for keeping important components below critical temperatures. In addition, an investigation into the effectiveness of Auxiliary Heat Removal Systems (AHRSs) at reducing cool-down hydrogen usage is reported on. It is found that significant opportunities for cool-down hydrogen reduction exist, both through computational optimization of the flowrate profile and through the inclusion of an AHRS to remove heat by less wasteful means.

Committee: John Horack Ph.D. (Advisor); Sandip Mazumder Ph.D. (Committee Member) Subjects: Aerospace Engineering; Nuclear Engineering

Master of Science in Engineering, Youngstown State University, 2020, Department of Mechanical, Industrial and Manufacturing Engineering

This project was funded by a company where some work is proprietary and is not recorded in this paper. The purpose of this project was to simulate, analyze and improve an enclosed methane combustion. The final goal was to reduce the overall pressure in the system along with determining if the system could be analyzed without the need of simulations. Simulation and Analysis of the combustion model requires a fundamental understanding of all the basic processes used. An understanding of the simulation software fluent along with the ability to manipulate the settings to what is required for the specific simulation being performed. An understanding of the chemical kinetics is required for proper setup of the simulation model. Prior to simulating the full model, multiple small simulations were performed to determine the settings needed for Ansys Fluent. Once these settings were determined then full model simulations with varying properties were performed. Based on both the simulations and literature it was found that when the combustion is performed at the stoichiometric ratio, the combustion is at its hottest adiabatic flame temperature and results in the highest pressures in the chamber. With changes to both the initial pressure and concentration of nitrogen the resulting pressures were determined to be lower than the base line model as expected. While these lower values were expected, there is a large percent change in the pressure across the model. The major findings from this project have been the interactions of the shock waves in the chamber. Depending on what is in the chamber, these shock waves can cause irreversible damage to the part. With the introduction of complex geometry in the chamber the approximation of the shock waves become much more complex and analysis of the part though simulation would be the best course of action in the determination of these shock waves. An attempt to lower the shock waves pressure peaks were made with results in d (open full item for complete abstract)

Committee: Stefan Moldovan PhD (Advisor); Kyosung Choo PhD (Committee Member); Kevin Disotell PhD (Committee Member) Subjects: Mechanical Engineering

Master of Science in Engineering, University of Akron, 2020, Mechanical Engineering

Studying human brains and spinal cords, or many other complex body parts for that matter, come with great challenges and risks when hoping to get accurate data, hopefully in real-time, in vivo, as opposed to in vitro or from a corpse. Of even more interest, are diseased members, since they possess unique traits that shine significant light into the medical community to help understand and treat countless disorders and pathologies. Having this information greatly improves the quality of life for the afflicted, but not to mention, the whole human race. Of particular interest here, is the cerebrospinal fluid flow, a water-like substance, that encases the spinal cord and pulses in and out of the brain's intracranial spaces. Upon entrance into the brain cavity from the spinal cord, it first encounters the cerebellum, the posterior lobes at the bottom of the brain. A lot of studies have been done, in vivo and in vitro, to understand its impact on the movement of the cerebellum, specifically in relation to a Chiari malformation which is characterized by herniation of the cerebellar tonsils. Pahlavian et al shows data from magnetic resonance imaging where the cerebellum of healthy patients moves approximately 100 microns. The work herein uses numerical software tools to hypothesize the cause of the cerebellum's movement. Sources vary widely about the actual material properties of the spinal cord and brain. But with the later data found from Klatt et al, estimates show material elasticity on the order of 1 kPa. With said material elasticity, numerical studies here concluded the cerebellum moves approximately 200 microns. Considering the broad variance among scientists about human tissue elasticities, fluid substance properties, geometry, etc., this was very close to Pahlavian's conclusion, thus fruitful. Two main contributors can lead to cerebellum movement, pressure and wall shear. It was determined from these numerical studies that pressure is the main contrib (open full item for complete abstract)

Committee: Francis Loth (Advisor); Sergio Felicelli (Committee Member) Subjects: Biomechanics; Biomedical Engineering; Engineering; Fluid Dynamics; Mechanical Engineering

Master of Science in Engineering, University of Akron, 2017, Mechanical Engineering

Polymer devolatilization is a vital process in polymer manufacturing and is significantly impactful on the successful creation of high quality polymers, meeting both rigorous product specifications and regulatory requirements. Polymers resulting from such processes have wide applications ranging from agricultural and biomedical solutions to aerospace components and even to modern day clothing and accessories. Although there are several popular methods used to accomplish the devolatilization process, this research focuses specifically on steam stripping, where superheated steam is used to remove any unwanted substances, such as volatiles and solvents, from the polymer mixture. This polymer mixture, referred to as "cement" and comprised of polymer and a cyclohexane solvent, undergoes mixing with superheated steam in a contactor to evaporate and remove the cyclohexane. Between the heat and the aerodynamic forces caused by the mixing, the liquid polymer experiences sheet breakup. The objective of the current study is to create a computational fluid dynamics (CFD) model that solves for the initial breakup of the liquid mixture, and then use the resulting diameter distribution to simulate the trajectory and multiphase mass transfer of the cement as it forms into smaller and smaller droplets. A parametric study is conducted in order to determine the effects of contactor geometry changes on the initial sheet breakup and the resulting impacts to the final polymer product quality. The purpose for modifying the geometry is to increase the uniformity of the breakup as well as reduce the amount of cement that sticks to the contactor walls. The use of CFD allows the industry partner for this research to try multiple different optimization solutions without interrupting production and spending large amounts of money on trial-and-error prototypes.

Committee: Abhilash Chandy Ph.D. (Advisor); Nicholas Garafolo Ph.D. (Committee Member); Scott Sawyer Ph.D. (Committee Member) Subjects: Mechanical Engineering; Polymers

Master of Science in Engineering, Youngstown State University, 2013, Department of Mechanical, Industrial and Manufacturing Engineering

Valves are critical components in a fluid flow network. Based on the type of fluid used, valves may suffer unforeseen wear and tear that might lead to an inadvertent failure. Major work in this thesis is focused on high pressure water valves that are used for descaling purposes. Controlling fluid flow at high pressures is not only challenging but also becomes time-wise critical. Failure of one such high pressure un-loader valves was studied first for the feasibility of my thesis work. A reverse flow operation was set in one such valve due to piping constraints established by industrial requirements. Experience and data recording showed that the premature failures of such valves by BOC Water Hydraulics were seen in months which lasted for years in standard operation. Computer simulation was being utilized to understand the fluid phenomena at such high pressures. The highly energized fluid from the descaling pump sets off a static pressure of 4300 psi at the valve inlet. It is responsible for continuous fluid flow rate of up to 208 gpm when the valve becomes fully open. Computational Fluid Dynamics (CFD) approaches are widely being utilized for fluid research in design optimizations. A Standard Turbulence model was used to understand the fluid flow variables using velocity/pressure contours for several possible valve opening positions. A very low pressure developed below the poppet seat of the valve suggests the onset of cavitation zones which may lead to leakage. Leakage at such a descaling pressure further accounts for cavitation and may which ultimately affect valve's overall performance resulting in cartridge replacement. Using CFD, the poppet valve assembly was modeled and simulated using ANSYS Fluent, commercially available CFD software. Low pressure below the atmospheric gage pressure in the valve body is found to be responsible for the initial onset of cavitation.

Committee: Ganesh Kudav PhD (Advisor); Param Adhikari MS (Committee Member); Suresh Sharma PhD (Committee Member) Subjects: Engineering; Mechanical Engineering

MS, University of Cincinnati, 2006, Engineering : Mechanical Engineering

The Micro Loop Heat Pipe (LHP) is a two-phase device that may be used to cool electronics, solar collectors and other devices in space applications. A LHP is a two-phase device with extremely high effective thermal conductivity that utilizes the thermodynamic pressure difference developed between the evaporator and condenser and capillary forces developed inside its wicked evaporator to circulate a working fluid through a closed loop. While previous experiments have shown reduction in chip temperature, maximum heat flux was less than theoretically predicted. This paper addresses the main problem with the past designs of top caps which has been the conduction of heat from the heat source to the primary wick. The new top cap design provides conduction pathways which enables the uniform distribution of heat to the wick. The provision of conduction pathways in the top cap increases the pressure losses and decreases the temperature drop. The feasible competitive designs of the top cap with conduction pathways from the fabrication point of view are discussed in detail. Calculation of pressure drop and temperature drop is essential for the determination of optimal solutions of the top cap. Approximate pressure drop was calculated for the top cap designs using simple 2-D microchannel principles. Finite element modeling was performed to determine the temperature drop in the conduction pathways. The conditions used for arriving at the optimal design solutions are discussed and presented. A trapezoidal slot top cap design and trapezoidal mesas top cap were chosen for fabrication as they were relatively easy to fabricate with available MEMS fabrication technologies. Geometry of the external vapor reservoir for the trapezoidal slot top cap was designed for optimum pressure drop. Variation of pressure drop in the top cap with respect to the porosity in the coherent porous silicon wick was discussed and analyzed in detail. The exact pressure drop calculations were performed numeri (open full item for complete abstract)

Committee: Dr. Frank Gerner (Advisor) Subjects: Engineering, Mechanical

Master of Science (MS), Ohio University, 2011, Mechanical Engineering (Engineering and Technology)

Flow uniformity through channels of a complex fuel cell stack is studied for several baffle arrangements using ANSYS Fluent, a computational fluid dynamics (CFD) package. Flow mal-distribution occurs from pressure differentials throughout the flow structure and causes a drop in stack performance. Three baffle arrangements were introduced into the flow structure and compared to a control case with no baffle in an attempt to improve the flow regime. A flow uniformity coefficient Γ was introduced to compare results from case to case. It was found that all three arrangements significantly increased flow uniformity, with the slotted baffle arrangement providing the most uniform flow. By increasing flow uniformity, the efficiency of the stack is also increased.

Committee: David Bayless (Advisor); Gregory Kremer (Committee Member); John Cotton (Committee Member); Greg Van Patten (Committee Member) Subjects: Engineering; Fluid Dynamics; Mechanical Engineering

Master of Science in Engineering, Youngstown State University, 2013, Department of Mechanical, Industrial and Manufacturing Engineering

Not only due to its versatility and inexpensive availability, lab-on-a-chip integrates multitasks for a complete µTAS. Due to easy portability in micro-devices, microfluidics has potential to revolutionize in many applications that include food, pharmaceutical, biomedical and chemical industries, etc. Mixing is inevitable for the analysis of trace chemicals, drugs, bio-molecules, fluidic controls in microfluidics, etc. Such miniaturized microfluidics had already proven better over bulky instrumentations, because of time and transportation required in handling. In this work, both active and passive were computationally studied. Passive mixing is considered with the mass fraction at different velocities of various mixer models when the fluids are in contact with each other. A two dimensional comparative analysis was performed to see the degree of mixing on two standard geometries including T and Y for general purposes. Along with standard geometries including T & Y, combinatory models with more than two inlet ports were also investigated using ANSYS Fluent, finite volume software. The engulfment flow was the major reason responsible for the mixing process. The engulfment flow was one of the major reasons responsible for the mixing process. Diffusion is a dominant phenomenon in passive mixing at the junction where various inlets meet and convective process becomes prevalent. Identification of geometrical correlation with the flow field variables and mixing parameters are crucial for better mixing design. The active mixing would be mathematically modeled with additional body force in the momentum equation. Thus, active mixers are externally activated for better mixing possibilities than the time consuming and possible complex geometries in passive mixing. Concentration variances over time at the outlet were simultaneously compared in all models for mixing. Also average concentration was tracked over time so as to confirm uniformity in mixing. Active circular mixers w (open full item for complete abstract)

Committee: Yogen Panta PhD (Advisor); Hyun Kim PhD (Committee Member); Ganesh Kudav PhD (Committee Member) Subjects: Engineering; Fluid Dynamics; Mechanical Engineering