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KC, AmarNumerical Simulations of Magnetohydrodynamic Flow and Heat Transfer
Master of Science in Engineering, University of Akron, 2014, Mechanical Engineering
Magnetohydrodynamic (MHD) natural convection in a porous medium with low- magnetic Reynolds number (Rem ) is investigated in a rectangular cavity with isother- mal walls on the left and right and adiabatic walls on the top and bottom. The validity of Darcy’s law is addressed for high-Rayleigh number (Ra) flows with high permeability, where the velocity-pressure gradient relationship transitions from lin- ear (i.e. the Darcy law) to nonlinear, due to the fact that the form drag due to solid obstacles is now comparable with the surface drag due to friction, which in turn re- sults in the Darcy-Forchheimer law. In addition, the effect of different magnetic field strengths in terms of Hartmann numbers (Ha) is also investigated for cavities for varying aspect ratios to analyze how the flow and thermal characteristics in a porous medium are influenced by the applied magnetic field. Here, the interaction between the fluid velocity and the electromagnetic forces gives rise to different flow scenarios. In particular, the influence of magnetic field under the varying conditions of convec- tive currents (through Ra) and length scales (through aspect ratios) on quantities such as stream function, temperature and Nusselt number, Nu is studied. Assess- ment of three regularization-based models and two eddy-viscosity-based subgrid-scale (SGS) turbulence models for large eddy simulations (LES) are carried out for MHD decaying homogeneous turbulence (DHT) and MHD transition to turbulence for the Taylor-Green vortex (TGV) through comparisons to direct numerical simulations (DNS). Simulations are conducted using the low-magnetic Reynolds number approxi- mation (Rem << 1) and the initially-isotropic turbulence problem has a Taylor scale Reynolds number (Re¿) of 120. LES predictions using the Leray-a, LANS-a, and Clark-a regularization-based SGS models are compared to the classic non-dynamic Smagorinsky and the dynamic Smagorinsky models. Regarding the regularization models, this work represents their first application to MHD decaying turbulence or transition-to-turbulence problems. Analyses of turbulent kinetic energy decay rates, energy spectra, and vorticity fields are made between the varying magnetic field cases. Overall, the regularization models did poorly compared to the eddy-viscosity models for all MHD cases, but the comparisons improved as the magnetic field increase in magnitude.

Committee:

Abhilash Chandy, Dr. (Advisor); Guo=Xiang Wang, Dr. (Committee Member); Siamak Farhad, Dr. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Darcy-Forchheimer, magnetohydrodynamic, Hartmann, Smagorinsky, large eddy simulations, Taylor-Green vortex

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;

Bruzzese, John ReedDevelopment Of An Electric Discharge Oxygen-Iodine Laser And Modelling Of Low-Temperature M=4 Flow Deceleration By Magnetohydrodynamic Interaction
Master of Science, The Ohio State University, 2008, Aeronautical and Astronautical Engineering
The present work addresses performance optimization of a small-scale, electric discharge excited, gasdynamic oxygen iodine laser (DOIL). For this, (i) nitric oxide has been added to the laser mixture, and (ii) iodine vapor was dissociated in an auxiliary electric discharge prior to its injection into the laser flow. The addition of NO has a significant effect on the laser performance, increasing small signal gain in the supersonic laser cavity from 0.05 %/cm to 0.08 %/cm. On the other hand, although large iodine dissociation fractions in the laser cavity have been achieved using an auxiliary discharge (up to 50%), only modest increase in gain was detected. The DOIL laser apparatus has been scaled up, with the main electric discharge volume increased by a factor of four and the flow rate through the laser doubled. The scaled-up laser has been tested using a nanosecond pulser / DC sustainer discharge or a capacitively coupled radio frequency discharge (CCRF) sustained at powers up to 2.7 kW and 4.5 kW, respectively. In both these cases, single-delta oxygen yield of up to 3-4% has been measured. Small signal gain up to 0.116 %/cm has been measured in the laser cavity while using the CCRF discharge to generate singlet delta oxygen. Numerical modeling of magnetohydrodynamic deceleration of a low-temperature M=4 flow was conducted using a three-dimensional compressible Navier-Stokes flow code. The results are in good agreement with recent experiments conducted at Ohio State, where flow deceleration by up to 2% has been demonstrated.

Committee:

Igor Adamovich (Advisor)

Subjects:

Engineering

Keywords:

DOIL; e-COIL; MHD; Magnetohydrodynamic; CFD; Laser; singlet delta oxygen;