Effects of recess depth and opening diameter on pressure measurement by recess mounted transducers in a hypersonic boundary layer

•The impact on measured data of recessed transducers was studied.•Spectrum, waveform, skewness and kurtosis of pressure fluctuations were studied.•Bispectrum analysis was adopted to study the nonlinear phase coupling.•Large recess depth and small opening diameter are likely to cause cavity resonance.•Small recess depth and large opening diameter are better in hypersonic flight test. Experimental measurements of pressure fluctuations in a hypersonic boundary layer were conducted based on recess mounted transducers and the effects of recess depth and opening diameter on fluctuating pressure characteristics were studied. The results showed that as the recess depth increased, the bulk of counter flow in the cavity enlarged with the decreased energy of large scale structures, and more small scale structures with relatively high frequency were generated which contributed to the multiscale structures with broadband frequency spectrum. Similarly, as the opening diameter increased, the low-frequency large scale structures inside the cavity had larger energy due to the shear flow entering the cavity having more mass and carrying larger energy, and the small scale structures with high frequency exhibited stronger dissipation intensity. The symmetric and stable flow filed was more likely to cause the cavity resonance, and the asymmetry and instability of the flow field for smaller recess depth as well as larger opening diameter could inhibit the cavity resonance. Compared to surface mounted, nonlinear phase coupling occurred between the flow structures caused by recess mounting which transfered the energy from high-frequency structures to low-frequency structures. On the whole, smaller recess depth and larger opening diameter are optimized in the hypersonic flight test on the premise of pressure sensors not destroyed by the harsh aerothermodynamic environment.