Sound field/flow field characteristics of supersonic jet impinging on inclined plate under different pressure ratios

In order to study the noise characteristics and sound source characteristics of the supersonic jet impinging on the inclined plate，the flow field and sound field of the supersonic jet under different pressure ratios were measured by high-frequency PIV （particle image velocimetry） and far-field noise.PIV measurement results can be used to observe the formation process of the shock grid and the impact of the inclined plate.The sound field measurement results can be used to capture the transition process of different tone frequencies in the free jet and the impinging jet as the pressure ratio increased.By comparing each tone mode and flow field mode one by one，the sound source characteristics of each tone mode can be distinguished.When pressure ratio was between 2.0-3.2，there were five tone modes：the tone of A mode was taken as the shear layer large-scale vortex shedding frequency，and the flow field presented a coaxial mode；the tone frequencies of the d and e modes were mainly taken as an impinging tone frequency；when the e mode appeared，the flow field transformed into a spiral mode，which was an unstable mode；when pressure ratio was more than 2.53，the tone mode was stable to a single mode B，and the tone of the B mode was taken as the screech frequency.The structure was converted back to the coaxial mode，and the screech frequency was not sensitive to the presence or absence of the inclined plate；the tone frequency of the B mode gradually decreased with the increase of the pressure ratio，and for the second harmonic frequency there was a strong sound wave radiation in the direction of the smaller amplitude of the fundamental frequency.