Computational test cases have been selected from archived sets of data acquired some years ago in wind-tunnel experiments on a clipped delta wing equipped with a hydraulically actuated trailing-edge control surface. In some of the experiments, the wing was subjected to pitching oscillations and control-surface oscillations. (The wing was stiff and thus did not undergo appreciable elastic oscillations; instead, it was mounted in such a way as to enable it to oscillate as a rigid torsionally sprung body.) The data obtained in the experiments included the static pressures and the real and imaginary parts of the first harmonics of dynamic pressures at a number of points on the upper and lower wing surfaces.

The significance of the experiments and the computational test cases lies in the design of the wing and in the need for experimental data to verify computational fluid dynamics (CFD) programs for use in analyzing and designing similar wings. The planform of the wing was derived by simplifying the planform of a proposed design for a supersonic transport airplane. A strake was deleted, the resulting planform was approximated by a trapezoid with an unswept trailing edge, and the twist and camber were removed. To facilitate pressure instrumentation, the thickness of the wing was increased to 6 percent of chord, as compared with 2.5 to 3 percent for the supersonic transport. The airfoil as thus designed had a symmetrical circular-arc section.

One of the consequences of increasing the relative thickness of a clipped delta wing is that transonic effects are enhanced for mach numbers near one; these effects are significantly stronger than would be the case for the thinner supersonic-transport wing. Also, the combination of the high (50.5°) leadingedge sweep and the sharpness of the leading edge results in the formation of a leading-edge vortex on the wing at relatively low (of the order of 3°) angles of attack. In addition, a shock develops over the aft portion of the wing at transonic speeds such that at some angles of attack, there is both a leading-edge vortex and a shock wave on the wing. Such cases pose a computational challenge.

The particular selection of test cases was made to illustrate trends for a variety of static, pitching-oscillation, and control-surface-oscillation conditions, with emphasis on effects associated with transonic flows. The dynamic cases were chosen for evaluation of unsteady effects under the corresponding nominally static conditions. The selection provides for parametric variation of the static angle of attack, frequency of pitching oscillation, frequency of control-surface oscillation, and mach numbers from subsonic to low supersonic values.

This work was done by Robert M. Bennett and Charlotte E. Walker of Langley Research Center.


NASA Tech Briefs Magazine

This article first appeared in the September, 2002 issue of NASA Tech Briefs Magazine.

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