A Real-Time Method for Estimating Viscous Forebody Drag Coefficients

Whitmore, Stephen A. and Hurtado, Marco and Rivera, Jose and Naughton, Jonathan W. (2000) A Real-Time Method for Estimating Viscous Forebody Drag Coefficients. Technical Report NASA/TM-2000-209015, Research Engineering, NASA Dryden Flight Research Center.

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Abstract

This paper develops a real-time method based on the law of the wake for estimating forebody skin-friction coefficients. The incompressible law-of-the-wake equations are numerically integrated across the boundary layer depth to develop an engineering model that relates longitudinally averaged skin-friction coefficients to local boundary layer thickness. Solutions applicable to smooth surfaces with pressure gradients and rough surfaces with negligible pressure gradients are presented. Model accuracy is evaluated by comparing model predictions with previously measured flight data. This integral law procedure is beneficial in that skin-friction coefficients can be indirectly evaluated in real-time using a single boundary layer height measurement. In this concept a reference pitot probe is inserted into the flow, well above the anticipated maximum thickness of the local boundary layer. Another probe is servomechanism-driven and floats within the boundary layer. A controller regulates the position of the floating probe. The measured servomechanism position of this second probe provides an indirect measurement of both local and longitudinally averaged skin friction. Simulation results showing the performance of the control law for a noisy boundary layer are then presented.

EPrint Type:	NASA Technical Memorandum
Keywords:	Base drag, Boundary layer, Hypersonic vehicles, Skin friction
Subjects:	Aircraft/Project: Multiple Aircraft (01 - 09) Aeronautics: (05) Aircraft Design, Testing And Performance Aircraft/Project: LASRE Aircraft/Project: A-5A Aircraft/Project: XB-70
ID Code:	68
Deposited On:	10 June 2004
Additional Information:	33 pages. Presented as AIAA 2000-0781 at the 38th Aerospace Sciences Meeting and Exhibit, January 10–13, 2000, Reno, Nevada. Stephen A. Whitmore and Marco Hurtado, NASA Dryden Flight Research Center, Edwards, CA; Jose Rivera, University of South Florida, Tampa, FL; and Jonathan W. Naughton, University of Wyoming, Laramie, WY.