不同压比状态下超声速射流冲击斜板的声场/流场特性

为研究超声速射流冲击斜板的噪声特性及声源特性，针对不同压比下，超声速射流流场及声场分别进行了高频PIV（particle image velocimetry)测量与远场噪声测量。PIV测量结果可观测到激波格栅形成过程以及冲击斜板对它的影响。声场测量结果可捕捉到自由射流与冲击射流中不同的纯音频率随压比增加的转变过程。通过一一对比各纯音模态与流场模态，可区分各纯音模态的声源特性。结果表明:当压比在2.0~3.2之间时，共出现五种纯音模态:A模态纯音频率为剪切层大尺度涡脱落频率，此时流场呈现同轴模态；d模态和e模态中纯音频率主要为冲击纯音频率，且e模态出现时流场转化为螺旋模态，这是一种不稳定模态；当压比大于等于2.53时，纯音模态稳定成单一模态B，B模态纯音频率为啸叫频率，其流场结构转化回同轴模态，啸叫频率对斜板的存在与否不敏感；啸叫频率随着压比的增加逐渐减小，其二次谐频在基频幅值较小的方向上会出现一个强声波辐射。 

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.