Passive control of surface pressure fluctuations in reattaching flows

Experiments assessing the effectiveness of passive control involving a porous surface and cavity underneath for reducing the level of surface pressure fluctuations in reattaching flows are reported. Measurements are made on a generic axisymmetric body, representative of a launch vehicle configuration, in the Mach number range of 0.8 to 1.2. The measurements consist of distributions of mean surface pressure and unsteady surface pressure fluctuations in the boat-tail separated region. The passive control significantly reduces the peak surface pressure fluctuations in the reattachment zone, even in the absence of a strong shock wave. The spectra of pressure fluctuations reveal that with passive control the energy is appreciably reduced over a wide range of frequencies