Stabilization of hypersonic boundary layer by combining micro-blowing and a porous coating

The extensive involvement of blowing in ablation and transpiration cooling directly influences the hypersonic boundary layer (HBL) transition. This work investigates the coupled effect of stabilization through micro-blowing and the corresponding porous blowing medium on a Mach 6 HBL flow. Linear stability theory (LST) and the e^N method are used to interpret the characteristics of stability, and direct numerical simulations are used to resolve the detailed flow field among the porous microstructures to verify the predictions of LST. The sole effect of micro-blowing is first investigated by emphasizing the locations of the blowing strip. The results show that micro-blowing alone can significantly excite the first mode but stabilize the second mode. In general, the HBL becomes unstable if the blowing strip is installed upstream of the synchronization points of the dominant disturbances, and otherwise becomes stable. In the context of the blowing medium, a porous coating can suppress high-frequency disturbances and help stabilize the HBL if the blowing strip is placed upstream of the synchronization points of the dominant disturbances. On the contrary, the coating can prematurely excite lower-frequency disturbances and degrade the overall stabilization when the strip is located in the dominant region of the second mode.