Development of a turbulent boundary layer over a micro-cavity array

Abstract A micro-cavity array has been identified as a potential passive boundary layer control device. This paper aims to provide insight into how a turbulent boundary layer develops over the surface of the array by characterizing the streamwise turbulent statistics of the boundary. Eleven distinct locations were investigated over the surface of the array under two free-stream velocity environments. Velocity data was obtained experimentally through single component hot-wire anemometry and under zero-pressure-gradient conditions. The statistics presented in this paper include turbulence intensity, sweep event intensity and pre-multiplied energy spectra, with all statistics normalized by friction velocity. The boundary was characterized for all locations for both a flat plate geometry and for when the array was installed. It was shown that the micro-cavity array was able to successfully attenuate streamwise turbulence statistics with maximum reductions in turbulence intensity and sweep intensity of 5% and 8.5% respectively. The pre-multiplied energy spectra were reduced by a maximum of of 26.9% at 50 wall units above the surface. Once the boundary had progressed approximately 15,000 wall units downstream of the first row of orifices the boundary spontaneously destabilized, resembling an unstable boundary affected by a rough wall.