Experiments on the development of natural disturbances in a hypersonic boundary layer on surfaces with microgrooves

The effect of surfaces with streamwise microgrooves on the development of natural disturbances in a hypersonic boundary layer is experimentally studied. The experiments are performed on a sharp cone at the free-stream Mach number M_∞ = 5.8. Microgrooves with rectangular and triangular cross sections are considered. The pressure fluctuations are measured on the cone surface at two stations upstream and downstream of the section with grooved surfaces. It is shown that the peak amplitude of the second-mode disturbances is much lower on the surface with microgrooves than on the solid surface, and the first-mode amplitude is always higher than that on the solid surface. It is found that the efficiency of stabilization of the second-mode disturbances depends on the groove depth and porosity. The greatest effect of stabilization is reached with the groove depth of about one quarter of the second-mode wave length. The growth rate of the first-mode disturbances is greater on the surfaces with microgrooves than on the solid surface.