运载火箭发动机喷流气动噪声特征及控制数值分析

This study focuses on severe fluctuating-pressure noise generated by carrier rocket engine jets. This study establishes an effective compressible LES-AA (acoustic analogy) computing technology using high-order low-dissipation and low-dispersion finite difference methods, to predict the high accuracy numerical and to analysis the noise generated by high Mach number supersonic jets of carrier rocket engines. The study reveals how several key parameters, such as jet Mach number, Reynolds number, temperature and nozzle-lip geometry eta., influence the jet sound field comprehensively, and then proposes an improved noise control method to reduce the jet noise during carrier rocket launching..The high Mach number supersonic jet noise is also an important scientific problem for compressible turbulent noise mechanism research. It includes complicated physical phenomena, such as shock-turbulent interaction, Mach wave radiation and acoustic feedback etc. It is difficult to study high Mach number supersonic jet noise, not only due to its multi-scale and strong discontinuity and other characteristics which makes the numerical simulation methods relatively sensitive, but also due to the complicated parameters effect mechanisms that make noise control very difficult. This research is promising not only to gain new understandings both in fundamental problem and engineering application, but also to provide reference for the noise control design of carrier rocket engines.

以运载火箭发动机喷流产生的严重压力脉动声场为研究对象，基于高精度、低色散、低耗散有限差分方法，建立有效的可压缩LES-AA(acoustic analogy)等计算手段，实现运载火箭发动机高Mach数超声速喷流噪声的高精度数值预测和分析，揭示喷流Mach数、Reynolds数、温度及喷口形状等关键参数对喷流声场的影响规律，进而提出改进的运载火箭发动机喷流降噪控制方法。 高Mach数超声速喷流噪声也是可压缩湍流噪声机理研究的重要科学问题之一。它包含激波-湍流相互作用、Mach波辐射、声反馈等复杂物理现象，不仅以其多尺度、强间断等特征使数值方法较为敏感，而且以其复杂的参数影响机制使降噪控制十分困难。本研究可望同时在基础问题和工程应用上取得新认识，为运载火箭发动机降噪设计提供借鉴。

针对运载火箭发动机喷流噪声，建立低耗散、低色散的DRP（dipersion- relation-preserving）空间离散格式、低存储优化Runge-Kutta时间推进格式、辐射无反射边界条件和声吸收区技术、选择性阻尼方法和自适应空间滤波技术等并行可压缩LES（large eddy simulation）方法，实现高速喷流噪声的高精度数值预测和分析。发展可穿透面FW-H（Ffowcs Williams-Hawkings）声外推方法，保证远距离声传播计算的保真性并大幅提高声远场求解的效率。. 针对Mach数为0.9亚声速喷流声辐射现象，仔细校核了喷流平均流和湍流统计结果，确定湍流模拟准确性。分析发现势流核末端剪切层涡融合、分裂、破碎等非线性流动演化形成的低波数波包产生声辐射。主导声辐射模态在远场低方位角占优，噪声峰值约在α=30º附近。最后，研究了喷口参数对声辐射影响。. 针对Mach数为1.95的欠膨胀超声速喷流，利用LES方法对其流动及噪声辐射计算分析。分析发现在势流核下游存在最后一个轮廓较清晰的胞格结构的区域是重要噪声源，此区间内湍流逐步侵入势流核，形成了激波胞格-湍流显著相互作用区。声场分析表明超声速喷流中Mach波辐射在下游占据主导，而宽频激波噪声则是上游近场噪声的主要成分。. 本项目深化了对高速喷流噪声现象的认识，揭示其形成机理，最终给降噪控制提供借鉴。.