A water tunnel investigation of the influence of Reynolds number on the high-incidence flow over double-delta wings

Abstract

There are several disagreements in the published literature on vortex interaction and bursting data obtained in various wind and water tunnel tests of double-delta wings at high angle of attack (AOA). Theretore a test program was carried out in the Naval Postgraduate School water tunnel using a 76/40 deg. baseline double-delta wing model to investigate the effect of Reynolds number. The program consisted of: (1) Flow vistialisation studies at tunnel speeds of O.2, O.6 and 1.0 ft/sec in the 0-30 deg. AOA range to determine the influence of flow Reynolds number on vortex trajectory/interaction and breakdown. (2) Laser Doppler Velocimetry studies of the flowfield to gain a better understanding of the vortex structure and verify the flow visualisation results. Comparison of the test results at these tunnel speeds (corresponding to nominal flow Reynolds number of 15,000, 45,000, and 75,000 indicates a change in the vortical flowfield structure. The strake and wing vortices do not coil up and the breakdown occurs earlier as the tunnel speed is increased.The trends in he interaction and bursting data at higher tunnel speeds appear to be in better agreement with previous wind tunnel data.