Experimental study of the effect of a passive porous coating on disturbances in a hypersonic boundary layer. 2. Effect of the porous coating position

The effect of the position of a passive porous coating on natural disturbances in a hypersonic boundary layer is studied experimentally. The experiments are performed in the flow around a sharp cone aligned at a zero angle of attack with the free-stream Mach number $\mathrm{M}_\infty=5.8$, stagnation temperature $T_0=370\pm 5$ К, and unit Reynolds numbers $\mathrm{Re}_{1\infty}=2.6\cdot10^6,4.6\cdot10^6,6.6\cdot10^6$, and $10^7$ m$^{-1}$. The wave characteristics of the boundary layer are calculated with the use of the linear stability theory for flow parameters corresponding to experimental values. A comparison of experimental and predicted results shows that the presence of a porous coating in the region where the second mode is unstable leads to reduction of its amplitude at the measurement point, whereas the presence of a porous coating in the region of second mode stability leads to enhancement of the amplitude.