Effect of two-dimensional micro-cavity surface on hypersonic boundary layer

For hypersonic boundary layer, the porous coating comprising small blind holes is an effective passive method that can delay the laminar-turbulent transition by damping the second mode wave. In this paper, surface with two-dimensional rectangular cavities with larger size comparable to the thickness of boundary layer is numerically investigated. The micro-cavity surface affects not only the second mode wave, but also the base flow due to the roughness effects. The numerical results showed that the total drag of base flow can be reduced by the micro-cavity surface compared to the smooth surface, more significant with smaller cavity width and higher porosity, while the cavity depth has little influence on the drag performance. The total drag can be further reduced when the micro-cavity surface suffers moderate static deformation under the pressure difference in the base flow. The micro-cavity surface is able to damp the second mode wave like the porous coating, and thus also has the potential to delay the transition. The effect on the second mode wave is stronger with higher porosity and smaller cavity width, while not monotonic with the cavity depth. The static deformation of structure causes local change of cavity characteristics, resulting in the second mode more damped over the deformed micro-cavity surface. When the structure dynamically responses to the fluctuating pressure of the second mode wave, the intensity of wave is slightly further decreased.