高超声速流动中噪声与湍流度的关系

在不可压缩流动中，湍流度对流动失稳与转捩的影响机制有很多研究成果，已发展了一些依据其大小预测流动转捩的模型应用于工程设计。但在高速可压缩流动中，湍流度很难测量，给该速域的流动转捩预测建模带来困难。近年来的研究表明，高速流场（马赫数≥3）中的噪声是影响流动转捩提前与推迟，甚至决定转捩途径的关键因素。但流场噪声与湍流度对流场的激励机制有没有内在联系，或流场噪声与湍流度理论上是否存在相互关联，迄今仍缺少理论分析结果。由于可压缩流场中噪声的测量相对容易，因此探讨流场噪声与湍流度之间的定量关系具有重要的理论意义和实用价值。讨论了Euler系统中各类双曲波特性，重点分析了流场声波中脉动压力与脉动速度的本质联系，从理论上得到了声压级与声致湍流度的关系。同时，为了对影响湍流度的因素有更全面的认识，导出了非声扰动与非声致湍流度的关系。为建立高速流动转捩预测模型和探讨天地一致性问题，奠定了一定的研究基础。

Noise-turbulence relationship in hypersonic flow

Extensive research on the influence of turbulence intensity on flow instability and boundary layer transition in incompressible flow has been conducted, resulting in the development and engineering application of some prediction models for boundary layer transition based on turbulence intensity. However, turbulence intensity is not easy to measure in compressible high-speed flow, posing significant difficulties in boundary layer transition prediction. Previous experimental results demonstrate that the noise level in high-speed flow (Mach number≥3) is one of the key factors affecting the boundary layer transition location and path. However, no theoretical conclusions have been drawn so far as to whether a relationship between the noise level and the turbulence intensity exists. Compared to the turbulence intensity, the noise level measurement is relatively easier in the high speed flow. Therefore, it is of theoretical significance and practical value to explore the quantitative relationship between the noise level and the turbulence intensity in the flow field. Typical disturbance waves in Euler’s system are discussed, focusing on the analysis of the essential correlation between the pressure fluctuations and velocity fluctuations. The theoretical relationships between the sound pressure level, the velocity curl and the turbulence intensity are derived, which is conducive to the establishment of a prediction model for high-speed boundary-layer transition and the exploration of the aerodynamic data correlation between flight and ground tests.