For a single-component perfect gas, entropy perturbations are associated with the difference between the overall density fluctuation and that coming from the acoustic perturbation. Entropy perturbations can generate sound when accelerated/decelerated by a non-uniform flow and this is highly relevant to thermoacoustic instabilities for gas turbines and rocket engines, and to noise emission for aero-engines. Widely used theories to model this entropy-generated sound rely on quasi-1D assumptions for which questions of validity were raised recently from both numerical and experimental studies. In the present work, we build upon an acoustic analogy theory for this problem. This theory was initiated by Morfey (J. Sound Vib. 1973) and Ffowcs Williams and Howe (J. Fluid Mech. 1975) about 50 years ago and extended recently by Yang, Guzmán-Iñigo and Morgans (J. Fluid Mech. 2020) to study the effect of non-plane entropy waves at the inlet of a flow contraction on its sound generation. Comparisons against both numerical simulations and previous theory are performed to validate the results.

对于单组分完美气体，熵扰动与整体密度波动与来自声学扰动的密度波动之间的差异有关。当由非均匀流动加速/减速时，熵扰动会产生声音，这与燃气轮机和火箭发动机的热声不稳定性以及航空发动机的噪声排放高度相关。广泛使用的理论来模拟这种熵产生的声音依赖于准一维假设，最近从数值和实验研究中提出了有效性问题。在目前的工作中，我们针对这个问题建立了声学类比理论。这一理论大约 50 年前由 Morfey (J. Sound Vib. 1973) 和 Ffowcs Williams 和 Howe (J. Fluid Mech. 1975) 提出，最近由 Yang 扩展，Guzmán-Iñigo 和 Morgans (J. Fluid Mech. 2020) 研究流动收缩入口处的非平面熵波对其声音产生的影响。对数值模拟和以前的理论进行比较以验证结果。