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首页> 外文会议>ERCOFTAC International Symposium on Engineering Turbulence Modelling and Measurements(ETMM6); 20050523-25; Sardinia(IT) >CHARACTERIZATION OF A SEPARATED TURBULENT BOUNDARY LAYER BY TIME-FREQUENCY ANALYSES OF WALL PRESSURE FLUCTUATIONS
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CHARACTERIZATION OF A SEPARATED TURBULENT BOUNDARY LAYER BY TIME-FREQUENCY ANALYSES OF WALL PRESSURE FLUCTUATIONS

机译：壁面压力波动的时频分析表征分离的湍流边界层

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摘要

An experimental investigation of wall pressure fluctuations generated by turbulent boundary layers (TBLs) over surface irregularities has been conducted in a backward-forward-facing step geometry simulating a large aspect-ratio cavity. Measurements are conducted by means of microphones flush mounted at the wall. The present paper is focalized upon the characterization of the local properties of the auto and cross-spectra in terms of both space and time and in account for the effects of the flow separations near the steps. It is shown that the classical approach for the cross-spectrum modeling, based on a pure exponential approximation, correctly applies even within the regions close to the steps, provided the exponential decay coefficient is correctly evaluated. The convection velocity computed along the cavity reveals that the hydrodynamic contribution to the pressure fluctuations is always dominant except for the region close to the forward-facing step where acoustic effects are the most relevant. The effect of the steps is also reflected onto the Probability Distribution Functions (PDF) of the coefficient of the exponential decay of the coherence function, obtained through the wavelet analysis of the pressure time series.
机译：在模拟大的长宽比空腔的后向-前向台阶几何形状中，进行了由表面不规则性上方的湍流边界层（TBL）产生的壁压力波动的实验研究。通过齐平安装在墙上的麦克风进行测量。本文着眼于在空间和时间方面对自动谱和互谱谱的局部特性的表征，并考虑了阶跃附近的流动分离的影响。结果表明，只要能正确评估指数衰减系数，基于纯指数近似的经典交叉谱建模方法就可以正确应用，即使在靠近阶跃的区域内也是如此。沿空腔计算的对流速度表明，除了靠近前向台阶的区域（声效应最相关）之外，流体动力学对压力波动的贡献始终占主导地位。这些步骤的影响也反映在通过压力时间序列的小波分析获得的相干函数指数衰减系数的概率分布函数（PDF）中。

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