Euler procedure for correcting two-dimensional transonic wind-tunnelwall interference

Abstract

Based on an optimization formulation, a procedure has been developed to evaluate Mach number and angle- of-attack corrections. The Euler equations are assumed to be the flow governing equations. To obtain efficient solutions for the optimization problem, the iterative solutions for the flow variables and the design parameters are simultaneously updated. This is done by using a scheme that eliminates the limitations of a previously developed scheme. In addition to the model lift and geometry, the procedure requires pressure measurements near the tunnel walls. The accuracy and efficiency of several optimization techniques are investigated. The effect of perturbing certain test conditions on the residual interference is investigated. IRCRAFT models are tested in wind tunnels to study their aerodynamic properties and to estimate their perfor- mance qualities. Because of wall interference effects, however, the properties observed in the wind tunnel differ from those observed under free-air conditions. To estimate correctly the free-air performance of the tested models and to achieve the maximum benefit from wind-tunnel tests for design improve- ments, it is necessary to determine the wall interference effects and to correct for them accurately. The classical procedure1 for correcting wall interference effects is based on linear theory. Although it provides insight into the features of wall interference, it does not produce sufficiently accurate formulas for practical use. A major source of error in the classical approach has been eliminated by wall interference correction procedures that replace the inaccurate homogeneous wall boundary conditions with measured flow properties. Procedures that require pressure measurements along a contour neighboring the tunnel walls,2 measurements of a single flow quantity along two contours,3 and measurements of two flow variables at a single contour4 have been developed. These and other methods summarized in Ref. 5 are applicable to linear, subsonic flows. Two-dimen- sional transonic wall interference correction procedures have been developed by Kemp^' 7 and Murman.8 These procedures use measured pressures near the tunnel walls and on the model surface. Solutions of the transonic small-disturbance equations are obtained and used to determine Mach number and arigle-of-attack corrections. The two-dimensional correction procedure presented here is formulated as an optimization problem. The Euler equations are assumed to be the flow governing equations, and the limitations of using the small-disturbance assumption are removed. Body-fitted coordinates are used to apply accurately the surface boundary conditions. The three-dimensional tran- sonic correction procedure developed in Ref. 9 includes a