Reduced Order Modeling in Control of Open Cavity Acoustics

Abstract : Aircraft with internal carriage of weapons or surveillance systems require active control strategies to limit high amplitude open bay acoustic resonances and to facilitate optimization of structure requirements and weapon/surveillance reliability. This paper focuses on communicating an investigation of the use of numerical simulation combined with Proper Orthogonal Decomposition (POD) model reduction methods to optimize an active control system for aircraft open cavity applications. Issues ad- dressed include characterizing shear layer and wake resonant responses, optimal steady blowing rates, the effect of open loop harmonic perturbations, use of POD for post-processing data to reduce storage requirements, and the use of the Nelder-Mead optimization procedure. Comparison of the wake and shear layer responses reveals why a wake response in aircraft is undesirable. This study has focused primarily on a freestream flow at M=0.85 with a cavity of aspect ratio l/d = 4.5. The results include the use of steady blowing injection up to M = 0.9 and harmonic forcing perturbations ranging in amplitude from M=0.005 to M=0.45. In the parameter space examined, fluid displacement had the largest effect. The best observed forcing reduced the buffet loading metrics by approximately 17 db.