Title:
Investigation of Transonic Drag Computations in
Aerodynamic Preliminary Analysis System (APAS)
Investigation of Transonic Drag Computations in
Aerodynamic Preliminary Analysis System (APAS)
Author(s)
Miller, Jeff
Advisor(s)
Olds, John R.
Editor(s)
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Abstract
The Aerodynamic Preliminary Analysis System (APAS) is often used in
conceptual design studies due to its low process times and relatively good results. APAS
is actually a front end to two separate analysis codes, Unified Distributed Panel (UDP)
and Hypersonic Arbitrary Body Program (HABP). APAS uses UDP to analyze subsonic
and supersonic runs, and HABP to analyze hypersonic runs. Concern exists over the process by which APAS calculates transonic drag. It is
common knowledge that an aircraft or spacecraft encounters a drag rise as is approaches
the sound barrier, which then tapers off again once the vehicle has gone supersonic. This
drag rise begins around a Mach number of 0.86, which is why most of today’s passenger
planes travel at or below that speed. Computer programs have been written that achieve
transonic drag results equivalent to those observed in wind tunnels and drop tests. The
manner in which APAS calculates drag in the transonic regime, and the accuracy of these
results was the focus of this project.
It was shown that APAS deals with transonic drag rise through the addition of a
wave drag term to the overall drag coefficient. Wave drag is caused by shock waves and
shock-induced separation. The method by which APAS calculates wave drag was
determined and compared to another code called WAVDRAG, which was also written at
NASA Langley. The two programs differ slightly in that WAVDRAG calculates zero-lift
wave drag, and APAS includes wave drag due-to-lift in it’s calculations. It was then
shown that neither WAVDRAG nor APAS calculate wave drag if the freestream Mach
number is less than 1.0. This yields incorrect transonic drag results, as the drag rise
should begin sub-sonically. However, for the purposes of APAS, the approximation is
probably “close enough.” The investigation was initially performed on six simple wing- body configurations, each of which was analyzed in APAS and WAVDRAG. APAS
results from the UDP analysis of three reusable launch vehicles (RLVs) designed by the
Space Systems Design Lab at Georgia Tech were also examined in order to find
consistency between theoretical wing-body configurations and configurations resulting
from real-world applications of APAS. Finally, a simple modification was done to one of
the configurations, resulting in lower wave drag
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Date Issued
2002-04-26
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Resource Type
Text
Resource Subtype
Masters Project
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