Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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2006 - 20102

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    Computational Fluid Dynamic Solutions of Optimized Heat Shields Designed for Earth Entry
    (2010) Meeroff, Jamie Gabriel; Lewis, Mark J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Computational fluid dynamic solutions are obtained for heat shields optimized aerothermodynamically using Newtonian impact theory. Aerodynamically, the low-order approach matches computational simulations within 10%. Benchmark Apollo 4 solutions show that predicted heat fluxes under-predict convective heating by 30% and over-predict radiative heating by 16% compared to computational results. Parametric studies display a power law reliance of convective heat flux on edge radius. A slender heat shield optimized for a single design point produces heat fluxes 1.8 times what was predicted using the Newtonian approach. Here, maximum heating decreases with the inverse cube of the base sharpness. Coupled vehicle/trajectory optimized designs are examined for lunar return (11 km/s) and Mars return (12.5 km/s) and show possible discrepancies for eccentric shapes using low-order empirical correlations. Ultimately, gains suggested by the low-order approach using complex geometries are not reflected in high-fidelity simulations. In some respects, the simpler shape is the ideal one
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    MULTIDISCIPLINARY OPTIMIZATION OF NON-SPHERICAL, BLUNT-BODY HEAT SHIELDS FOR A PLANETARY ENTRY VEHICLE
    (2006-07-03) Johnson, Joshua Elijah; Lewis, Mark J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Gradient-based optimization of the aerodynamic performance, static stability, and stagnation-point heat transfer has been completed to find optimal heat shield geometries for blunt-body planetary entry vehicles. In the parametric study, performance trends have been identified by varying geometric parameters that define a range of cross-sections and axial shapes. Cross-sections considered include oblate and prolate ellipses, rounded-edge polygons, and rounded-edge concave polygons. Axial shapes consist of the spherical-segment, spherically-blunted cone, and power law. By varying angle-of-attack and geometric parameters, the aerodynamics, static stability, and heat transfer are optimized based on Newtonian impact theory with semi-empirical shock-standoff distance and stagnation-point heat transfer correlations. Methods have been verified against wind tunnel and flight data of the Apollo Command Module and are within 15% for aerodynamic coefficients and stagnation-point heat fluxes. Results indicate that oblate parallelogram configurations provide optimal sets of aerothermodynamic characteristics.