自由来流角度影响下壁面湍流脉动压力波数—频率谱的大涡模拟计算分析研究

壁面湍流脉动压力是重要的流噪声声源,对壁面湍流脉动压力及其波数—频率谱进行数值计算是流声耦合领域的重要课题。文章在已有工作的基础上,采用大涡模拟方法(LES)结合动态亚格子涡模型(DSL)与千万量级的精细网格,对不同自由来流角度影响下壁面湍流脉动压力及其波数—频率谱进行了数值计算与分析。首先,介绍了大涡模拟基本方法,包括:大涡模拟的物理内涵、基本方程以及所采用亚格子涡模型的表达式。其次,介绍了湍流脉动压力波数—频率谱及其计算与分析方法。再次,对不同自由来流角度情况下的湍流脉动压力及其波数—频率谱进行了计算,并将计算结果进行了比较分析,深入讨论了自由来流角度对湍流脉动压力及其波数—频率谱的影响。结果表明,在自由来流角度影响下,湍流脉动压力及其波数—频率谱主要参数(包括波数—频率谱的谱级峰值、迁移脊在波数—频率域内的分布范围、迁移速度和无量纲迁移速度等)均发生了明显变化,说明自由来流角度对湍流脉动压力波数—频率谱有显著影响,且边界层内湍流脉动压力的能量主要沿流向分布。因此,为了更加准确可靠地研究边界层内湍流脉动压力的主要统计特性及其波数—频率谱,传感器阵列或监测点阵列布置方向应与当地流向(局部剪应力线或摩擦力线)一致。

Investigating the effects of free-stream velocities on turbulent wall pressure fluctuations and their wavenumber-frequency spectra at high Reynolds numbers using Large Eddy Simulation

Turbulent wall pressure fluctuations beneath turbulent boundary layers are important sources of flow noise. The computation and discussion of wall pressure fluctuations and their wavenumber-frequen-cy spectra are hot topics in the field of flow-acoustic coupling. In this paper, wall pressure fluctuations of different geometries at high Reynolds numbers and their wavenumber-frequency spectra are computed us-ing large eddy simulation (LES) with appropriate sub-grid scale model, grid number and discretization meth-ods, in order to investigate the effects freestream velocities. The Reynolds number is up to Re=1.02×107 and the computed results are discussed in detail based on previous research by the author. And, some funda-mentals of the numerical simulation are presented, including the philosophy of LES, formulations of sub-grid scale models, discretization methods and boundary conditions. Secondly, the definition of wavenum-ber-frequency spectra and the approaches of their analysis and computation are demonstrated. Finally, tur-bulent wall pressure fluctuations as well as their wavenumber-frequency spectra under different freestream velocities are computed and analyzed in detail. The results show a remarkable change of the wavenumber-frequency spectra as affected by various freestream velocity angles and the kinetic energy of turbulent wall pressure fluctuations is mainly distributed along the flow direction. Based on detailed analysis of the com-puted results, it is recommended that the sensor array should be allocated along the local flow direction (or the local wall shear stress), in order to study the statistical characters or the wavenumber-frequency spec-tra more accurately.