Aero-optical Analysis of Shear Layers over 2-D Cavities with Steady and Pulsed Blowing and Comparisons with Experimental Data

Abstract

Prediction and control of optical wave front distortions and aberrations in a high energy laser beam due to interaction with an unsteady highly non -uniform flow field is of great importance in the development o f directed energy weapon systems for an Unmanned Combat Air Vehicle (UCAV). Unsteady shear layer over the weapons bay cavity is the primary cause of this distortion of optical wave front at the time of ejection of laser guided weapon from the cavity. Both passive and active control devices have been proposed in the literature to suppress the cavity oscillations. In a previous paper (Part I: AIAA 2004 -2122), we performed numerical simulations for a L/D=4 cavity (L=width and D=depth of the cavity) with a shar p leading edge and curved leading edges of three different radii using steady and pulsed blowing at the leading edge in a direction normal to the free stream. Computations were compared with the experimental data from the University of Notre Dame for root mean square Optical Path Difference (OPD rms ). It was shown that there was no significant reduction achieved in OPDrms by using active flow control with steady and pulsed blowing. In this paper, we perform numerical simulations for a L/D=4 cavity with curve d downstream edges of three different radii using steady and pulsed blowing at the sharp leading edge in a direction normal to the free stream. It is shown that the curvature at the downstream edge of the cavity helps in reducing the OPDrms with active flo w control (in contrast to the minimum effect in reducing OPDrms by introducing curvature at the leading edge of the cavity).