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Date of Award
Master of Science (MS)
High-speed vehicles experience different flow regimes during flight due to change in atmospheric density with the altitude. In the low earth orbit, due to decrease in density the flow experiences rarefaction. The effect of rarefaction is characterized by the non-dimensional parameter, the Knudsen number Kn (= λ/L, where λ is the mean free path and L is a characteristic length). At low Knudsen numbers of O (0.001 to 0.25), the flow is characterized to be in ‘slip regime.’ In the slip regime, the flow field can be calculated by employing the Navier-Stokes equations with slip velocity and temperature jump boundary conditions at the wall. To predict the rarefaction effect in the slip flow regime, Maxwell proposed the slip boundary conditions at the wall. In this thesis, a UDF (User Defined Function) which employs the slip boundary condition model of Maxwell is applied in the CFD solver ANSYS FLUENT to solve the compressible Reynolds Averaged Navier-Stokes (RANS) equations in conjunction with the Shear-Stress-Transport (SST) k-ω turbulence model to simulate the flow past a blunt body in hypersonic flow. In addition, the effects of chemical reactions due to dissociation of air or due the gases other than air on the flow field are considered. The numerical solutions are obtained with both no-slip and slip boundary conditions at several Knudsen numbers (Kn = 0.0003354, 0.00167, 0.0167, and 0.04180) for flow past two different blunt bodies to evaluate the effect of rarefaction and chemical reactions on heat transfer and drag. Comparisons are made with the experimental data and DSMC solutions available in the literature. In addition, a blunt body shape at different Knudsen numbers is optimized with a multi-objective Genetic Algorithm for reducing both the drag and heat transfer.
David Peters, Qiulin Qu
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