Finite-length porous surfaces for control of a turbulent boundary layer

Abstract

This study investigates the potential of finite-length porous surfaces with a subsurface chamber for the control of the turbulent boundary layer. The effect of the subsurface chamber on the boundary layer is investigated by hot-wire anemometry measurements of the boundary layer response to different chamber configurations. Three different chamber configurations were investigated: a common cavity that connected the array of surface perforations, a locally reacting chamber with individual cavities underneath each perforation, and chambers that connected the perforations in streamwise or spanwise flow directions. It was found that a common backing cavity and individual cavities reduced the peak turbulence intensity, whereas the test case with streamwise or spanwise channels increased the turbulence intensity and strengthened large-scale turbulent structures within the boundary layer. While both common and individual cavities were effective in reducing turbulence, the individual cavities created a larger reduction in the pre-multiplied spectrum with an average of 80% at large scales compared to between 40% and 60% reduction at large scales for common cavities with different volumes. Hence, a short porous surface with individual cavities underneath each perforation was found to be the most effective turbulence-reducing configuration among the investigated cases.