Investigation of Support Interference in High-Angle-of-Attack Testing

Abstract

An investigation was undertaken to understand support interference in high-angle-of-attack testing with particular emphasis on premature vortex breakdown induced by struts. In static experiments efforts concentrated on the support geometry and its location with respect to leading-edge vortices generated by delta wings. Extensive e ow visualization studies show that vortex breakdown induced by a dummy support might move over the wing depending on theangleofattack andthelocation of thesupport.As thelateral distancebetweenthevortex axisand support is varied, static hysteresis of vortex breakdown location was observed, which will have very important implications on forcemeasurements in wind-tunnel testing. The results also suggest that support interference is more important for slender wings. To separate the effects of time-dependent vortex strength and support interference, the model was kept stationary, and a dummy support was oscillated in the spanwise direction in the oscillatory experiments. It was observed that vortex breakdown location oscillates with large amplitudes at low frequencies, but does not show any response at high frequencies, indicating that the frequency response is similar to that of a low-pass e lter. Variation of phase-averaged breakdown location showed hysteresis loops and time lags, which are largerfor a thin e at platethan a circularcylinder. Theresultssuggestthatsupport interferenceproblems aremore complex in transient experiments.