与气动噪声相关的湍流模型及计算方法

陆利蓬 柳阳威 吴子牛 英基勇 方剑

摘要：针对气动噪声计算问题，经过两年的研究，主要进展如下： 1. 研究了高精度湍流模拟技术的数值方法。首先发展了一套基于高阶有限差分格式的流场求解器，并进行了系统测评；在此基础上，针对激波模拟精度，提出了带宽耗散优化方法（BDOM），发展了MP-LD 格式，结果表明MP-LD 格式对小尺度流动结构的捕捉能力以及对湍流的模拟效率要显著优于常规的高阶激波捕捉格式。 2. 采用高精度湍流模拟技术研究了复杂流动机理。利用MP-LD 格式和ASTR 程序，对激波/各向同性湍流干涉（SITI）和激波/湍流边界层干涉（SBLI）等进行了DNS 和机理性的研究。结果表明：湍流脉动之间的非线性作用使得大尺度湍流结构向各向同性恢复的过程更加复，而小尺度脉动结构则更容易恢复各向同性；由于来流速度脉动的影响，激波表面形状会发生变形，较高的来流速度脉动会导致当地激波位置更靠近下游，并增加激波的强度。 3. 研究了压气机三维角区分离流动机理和湍流模型改进。针对角区分离流动，首先开展了先进实验测量和高精度数值模拟，为机理研究和湍流模型改进提供丰富的数据库。其次，提出了基于湍流非平衡输运特性改进湍流模型的新方法，并针对SA湍流模型，提出了两种改进方法：一是修正模型系数Cb1，二是基于当地螺旋度计入湍流能量反传物理机制。其中，基于螺旋度改进可以“自适应”计入湍流非平衡输运特性，可以“自适应”实现对不同工况下压气机三维角区分离流动的准确模拟。 4. 研究了压气机转静干涉机理和时均模拟方法。针对转静干涉噪声，团队提出了时均模拟技术和线性谐波法相结合的快速非定常数值模拟思路。本课题首先采用非定常数值模拟技术，研究了转静干涉机理。其次改进了交界面处理方法，深入分析了确定性相关项的分布特点和对时均流场的影响特性，发展了确定性相关项模型，发展完善了时均模拟技术，为下一步和线性谐波法相结合，实现对转静干涉噪声源的快速非定常计算，提供坚实的基础。 5. 建立了气动声学知识库系统和噪声机理知识。首先建立了国际上首套气动声学知识库系统；其次对大攻角超音速流动，发现了机翼上表面存在一种激波/滑移面共存结构，发现了一种新的气动噪声来源；最后针对气动声学重要来源之一的点涡与物体的相互作用，建立了一套点涡群对多物体受力影响的基本理论。

关键词：气动噪声；湍流；数值模拟

Turbulence models and numerical methods for aero-acoustics

Abstract：The mainly development of the research work in the first two years is divided into five parts. 1. A high-fidelity flow solver is developed and evaluated in the study. To improve numerical scheme for shocks， the band width dissipation optimization method （BDOM） is developed. A high-order MP-LD scheme， based on BDOM is developed and assessed. The results show that MP-LD scheme is much better than the conventional high-order shock-capturing schemes in resolving small-scale flow structures and turbulent motions. 2. The DNS researches of shock/isotropic turbulence interaction and shock/turbulent boundary layer interaction are conducted. The return to isotropy of the turbulence downstream the normal shock is complex due to the nonlinear interaction between turbulence fluctuations. The shock surface is distorted by the inlet turbulence velocity fluctuations. Higher velocity fluctuations will make the local shock surface further downstream and increase the shock strength. 3. To investigate the corner separation in compressors， advanced experimental techniques and high-fidelity numerical simulations are conducted， and abundant database are achieved. A new modification approach for turbulence model is proposed based on turbulence transport nature. Two effective modified methods for SA model are achieved： one is to modify constant Cb1； the other is to take account of the energy backscatter by using relative helicity density. The result indicates that the modification based on helicity is self-adaptive for different conditions. 4. Investigation for rotor-stator interaction （RSI） noise prediction method is studied. Firstly， unsteady simulation is conducted to study RSI mechanism. Then the influence of rotor-stator interface treatment is improved. The distribution characteristics of deterministic correlations are analyzed and the influence of some factors on the time-averaged flow field is further studied. Based on above studies， an exponent decay deterministic correlation model is proposed. 5. Knowledge management system for aero-acoustics is set up and some acoustic flow mechanisms are studied. A new triple flow structure exists for a supersonic flow around a F15 fighter model at the high angle of attack. The Kelvin Helmholtz instability for the slip line would provide a new source of noise. The role of the body by including image vortex rings in the vortex ring model is studied and the body image effect reduces the lift force is found.

Keywords：Aero-acoustics； turbulence； Numerical Methods

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