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You searched for +publisher:"University of Oklahoma" +contributor:("Walters, Keisha B."). Showing records 1 – 2 of 2 total matches.

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University of Oklahoma

1. Wang, Huiyu. Analytical and computational modeling of multiphase flow in ferrofluid charged oscillating heat pipes.

Degree: PhD, 2020, University of Oklahoma

Electromagnetic-based energy harvesting materials and devices have emerged as a prominent research area in the last ten years, especially systems using ferrofluidic induction—a process that generates voltage via the pulsation of a ferrofluid (iron-based nanofluid) through a solenoid. This work includes the development of an analytical model and computational modeling methods to investigate ferrofluid pulsating flow within an energy harvesting device and the mass and heat transfer performance of a two-phase closed thermosyphon (TPCT) and oscillating heat pipe (OHP). First, an analytical model is proposed to predict the induced electromotive force (EMF) based on the flow behavior and magnetic properties of a pulsating ferrofluid energy harvesting device. The model identifies key parameters for describing and optimizing induction for ferrofluid pulsing through a solenoid. Data from a previously documented experimental study was used to validate the analytical model, and both the experimental data and analytical model show the same trends with the induced EMF increasing as a function of pulsating frequency and magnetic field strength as a higher percentage of the ferrofluid nanoparticle moments are aligned. Second, computational fluid dynamics (CFD) simulations were performed to predict the heat transfer performance of a TPCT. Simulations were performed using a three-dimensional finite-volume flow solver (ANSYS Fluent) with a pressure-based scheme for the solution of the continuity and momentum equations, volume-of-fluid method for resolution of the liquid-vapor phase interface, and a temperature-dependent model for interphase mass transfer by evaporation and condensation. Different model and numerical scheme combinations were investigated to identify an efficient and consistently accurate method using currently available software tools. To address issues with previously published simulation methods violating the conservation of mass, a new variable saturation temperature model was tested along with mass transfer coefficients based on the vapor-liquid density ratio and more physically realistic boundary conditions. The variable saturation temperature model significantly mitigated mass and energy imbalance in the simulations, for both constant heat flux and convection condenser boundary conditions. In addition, for the VOF discretization the Geo-Reconstruct scheme was found to be more accurate than the Compressive scheme available in Fluent without additional computational cost. Third, simulations of a vertical OHP were performed using the CFD methodology developed for the TPCT system. Results show simulations using appropriate values for the evaporation and condensation mass transfer time relaxation parameters and the new variable saturation temperature model are in good agreement with the available experimental data. For the OHP system, using the Compressive discretization scheme for the VOF model allowed for computationally efficient simulation. It is believed that the advances in analytical and computational modeling… Advisors/Committee Members: Walters, D. Keith (advisor), Walters, Keisha B. (advisor), Ruyle, Jessica E. (committee member), Shabgard, Hamidreza (committee member), Vedula, Prakash (committee member), Garg, Jivtesh (committee member).

Subjects/Keywords: Heat Transfer; Computational fluid dynamics (CFD); Electrodynamic energy harvesting

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Wang, H. (2020). Analytical and computational modeling of multiphase flow in ferrofluid charged oscillating heat pipes. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/324967

Chicago Manual of Style (16th Edition):

Wang, Huiyu. “Analytical and computational modeling of multiphase flow in ferrofluid charged oscillating heat pipes.” 2020. Doctoral Dissertation, University of Oklahoma. Accessed February 28, 2021. http://hdl.handle.net/11244/324967.

MLA Handbook (7th Edition):

Wang, Huiyu. “Analytical and computational modeling of multiphase flow in ferrofluid charged oscillating heat pipes.” 2020. Web. 28 Feb 2021.

Vancouver:

Wang H. Analytical and computational modeling of multiphase flow in ferrofluid charged oscillating heat pipes. [Internet] [Doctoral dissertation]. University of Oklahoma; 2020. [cited 2021 Feb 28]. Available from: http://hdl.handle.net/11244/324967.

Council of Science Editors:

Wang H. Analytical and computational modeling of multiphase flow in ferrofluid charged oscillating heat pipes. [Doctoral Dissertation]. University of Oklahoma; 2020. Available from: http://hdl.handle.net/11244/324967


University of Oklahoma

2. Jamal, Tausif. Advanced Turbulence Modeling Strategies Within the Hybrid RANS-LES Framework.

Degree: PhD, 2020, University of Oklahoma

Reynolds Averaged Navier-Stokes (RANS) models still represent the most common turbulence modeling technique used in Computational Fluid Dynamics (CFD) today. RANS models are preferred primarily due to their relatively low computational demand and ease of use. The general RANS framework utilizes the ensemble averaged form of the Navier Stokes equations in which all turbulent scales are modelled, and hence requires reduced computational effort compared to scale resolving methods. Despite their popularity, RANS models have been found to perform poorly in flows with separated shear layers, unsteady wakes, and temporally evolving flows. There has been ongoing progress towards high-fidelity methods such as Large Eddy Simulation (LES) to more accurately represent these flow features. LES models apply filters to the equations of fluid motion to resolve the large turbulent structures that are responsible for energy transfer. The smaller scales however, are represented using a sub-grid scale (SGS) model. LES models perform well in separated shear layers where large eddies dictate the energy and momentum transfer, due to the small time and length scales associated with near wall flow. The costs associated with LES are a major limiting factor in their adoption in industrial and academic research. This has led to the development of Hybrid RANS-LES (HRL) models which offer improved performance over RANS models while being relatively inexpensive compared to LES models. The hybrid modeling approach aims to provide the best of both worlds. In hybrid models, LES models are used far away from the wall to resolve large scale structures primarily responsible for the transfer of momentum and energy, while the wall bounded turbulence is treated using a RANS model. However, HRL models suffer from inherent drawbacks associated with their handling of RANS to LES transition in addition to a high degree of grid sensitivity. The present study proposes advanced turbulence modeling strategies within the hybrid RANS-LES class of models. Major contributions include: (i) evaluation of RANS and hybrid RANS-LES models for separated and non-stationary flows, (ii) development of time-filtering techniques for the dynamic Hybrid RANS-LES (DHRL) model to improve predictive capabilities for non-stationary periodic and non-periodic flows, and (iii) a new variant of the DHRL model for complex turbulent flows to address a known weakness in the DHRL formulation. First, the performance of the DHRL model is evaluated against popular RANS and HRL models for flow over a three-dimensional axisymmetric hill. DHRL model results indicate superior prediction of mean flow statistics and turbulent stresses. However, some discrepancy in Reynolds stress prediction and the lack of a smooth LES-mode away from the wall is observed. Second, static and dynamic time filters are implemented to extend the DHRL model from an ensemble averaged framework to a non-stationary framework. Results once again indicate superior model performance when compared to other models investigated.… Advisors/Committee Members: Walters, Dibbon K. (advisor), O'Rear, Edgar (committee member), Walters, Keisha B. (committee member), Garg, Jivtesh (committee member), Shabgard, Hamidreza (committee member), Vedula, Prakash (committee member).

Subjects/Keywords: Computational Fluid Dynamics; Turbulence Modeling; Numerical Methods; Mechanical Engineering

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Jamal, T. (2020). Advanced Turbulence Modeling Strategies Within the Hybrid RANS-LES Framework. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/324966

Chicago Manual of Style (16th Edition):

Jamal, Tausif. “Advanced Turbulence Modeling Strategies Within the Hybrid RANS-LES Framework.” 2020. Doctoral Dissertation, University of Oklahoma. Accessed February 28, 2021. http://hdl.handle.net/11244/324966.

MLA Handbook (7th Edition):

Jamal, Tausif. “Advanced Turbulence Modeling Strategies Within the Hybrid RANS-LES Framework.” 2020. Web. 28 Feb 2021.

Vancouver:

Jamal T. Advanced Turbulence Modeling Strategies Within the Hybrid RANS-LES Framework. [Internet] [Doctoral dissertation]. University of Oklahoma; 2020. [cited 2021 Feb 28]. Available from: http://hdl.handle.net/11244/324966.

Council of Science Editors:

Jamal T. Advanced Turbulence Modeling Strategies Within the Hybrid RANS-LES Framework. [Doctoral Dissertation]. University of Oklahoma; 2020. Available from: http://hdl.handle.net/11244/324966

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