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NIA Seminar by David Riggins |
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Date: February 8, 2006
Time: 10:30am
Location: NIA, Rm 137
Force-Based Performance Analysis and the Role of Entropy in High-Speed Aero/Propulsive Flow-Fields
David W. Riggins, University of Missouri - Rolla
Computational and analytical results presented will encompass two ongoing and related activities: 1) forward facing injection from blunt bodies in high-speed flows when coupled with upstream deposition of energy will be shown to result in large decreases in overall drag and heat transfer. Additionally, the problem of upstream-directed injection jet instability will be shown to be significantly reduced by the coupling of the two techniques (injection and upstream energy deposition); this allows the jet to penetrate far upstream and stabilize within bounds. Cases will be shown in which the overall drag is only 20 to 30% of the base-line drag, heat transfer is minimal, and jet stabilization and forward penetration is ensured; the role of active control for drag minimization is explored. The relative force-based performance demonstrated by these simple cases will then be illustrated from a preliminary examination of their fundamental second law (entropy-generation) characteristics. 2) The second (related) part of the results shown will then focus on the more general development of a common currency for loss assessment/performance analysis for the aerodynamics and propulsion sub-systems of a complete aerospace vehicle with particular focus on high-speed flight. Specifically, theory, methodology, and example applications are developed and shown for the systematic analysis (auditing) of overall vehicle forces in terms of irreversibility (entropy) and heat. The role of overall entropy generation and wake mixing processes in the production of vehicle forces in atmospheric flight will be discussed and clarified. The direct analytical relationship between entropy, wake mixing processes, and overall force production for the vehicle will be shown from fundamental considerations of the global control volume with inclusion of the wake in the analysis. The analysis will then be further developed for the completely general problem of an aerospace vehicle with variable specific heats, thermal loading, variable composition, fuel injection, and chemical reaction. These fundamental second-law analyses are finally applied and demonstrated in order to explain computational results obtained for a selected high-speed (complete vehicle) air-breathing configuration as well as to fully diagnose and explain the earlier results obtained for forward-facing injection from simple blunt bodies.
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