Study of Asymptotic Theory of Transonic Wind Tunnel Wall Interference
Final rept. 30 May 1982-30 Aug 1983
ARNOLD ENGINEERING DEVELOPMENT CENTER ARNOLD AFB TN DIRECTOR OF MAINTENANCE (DOM)
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Asymptotic procedures were considered for two limiting cases of wind- tunnel interference assessment on transonic models. The first corresponds to slender configurations representative of fighter aircraft, and the second is associated with high aspect ratio shapes related to bombers and transports. In the first instance, solid cylindrical walls of radius much greater than the chord lead to interference effects on the drag of a greater magnitude than the lift. A similarity law was discovered for this effect in which the normalized drag correction is proportional to the product of the blockage ratio, and a function of the free-stream and tunnel perturbation to the transonic similarity parameter. On the basis of this law, alterations to the similarity parameter can be sought to obtain interference-free conditions for the drag. In addition, the theory provides systematic means of extrapolating to zero model size. A numerical problem was formulated whose solution gives the structure of the interference flow field. For the high aspect ratio case associated with rectangular cross-section solid walls, asymptotic methods give a framework which is a generalization of lifting line theory for unconfined flows. Near the wing, the flow retains the two-dimensional strip theory character of the free-field situation. By contrast, the far field consists of a bound vortex, shedding trailing vorticity at a rate proportional to the spanwise gradient in the spanwise load distribution.
- Fluid Mechanics