Shallow cavity noise influencing by boundary-layer thickness at supersonic speeds

An experimental investigation had been constructed to perform effects of boundary-layer thickness on shallow cavity noise characteristics,and sound pressure level(SPL) distributions and sound pressure frequency spectrum(SPFS) characteristics inside shallow cavities with length to depth ratios of 12 and 15 at supersonic speeds were analyzed.The data presented herein was obtained over a Mach number of 1.5 at a Reynolds number of 2.26×10⁷ per meter.The results show that decrease in ratios of the boundary-layer thickness to the cavity depth(δ/D) causes flow oscillation amplification,noise enhancement inside the shallow cavities.Decrease in δ/D leads to obvious increases in SPL in the most frequencies at different positions measurement in the forward and rearward of the shallow cavities.Shock waves in the middle of the shallow cavities which induced by supersonic free-stream flow disturb the flow structure,which makes boundary-layer flow characteristics has few influences on the aeroacoustic characteristics in the middle of the shallow cavities.Generally,decrease in boundary-layer thickness has significant influences on flow oscillations and noise characteristics of shallow cavity at supersonic speeds.