Direct numerical simulations are carried out of boundary layer flow at Mach 6 over a porous surface, in which a Mack mode of instability is excited. The pores are resolved rather than modelled, allowing an evaluation to be made of the accuracy of simplified one-dimensional models used in previous investigations based on linear stability theory. The simulations confirm the stabilizing effect of porosity. The effect is stronger in the simulations than in the corresponding theory. From comparisons of spanwise grooves, streamwise slots and square pores it appears that the detailed surface structure is not as important as the overall porosity and the hydraulic diameter is able to collapse the results for different pore shapes to good accuracy. When the porous surface consists of fewer larger pores, the flow is noisier, with sound waves generated at the pore edges.
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Sandham et al. (2009) studied this question.
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