用子波谱分析壁湍流多尺度结构的能量传递

Wavelet Spectrum Analysis on Energy Transfer of Multi-Scale Structures in Wall Turbulence

测量了壁湍流不同法向位置的流向速度.用子波变换研究湍流能谱,表明子波全局谱是Fourier谱按子波尺度加权平均的结果,高阶消失矩的子波变换能够表征湍谱的衰减特性;子波局部谱显示边界层内涡的变形、破碎等现象与边界层法向位置有关,含能涡结构呈多尺度分布,随着测点远离壁面,含能涡的尺度增大;在缓冲区出现更高频的小尺度含能涡,在外区能量集中在低频大尺度涡结构中,含能涡的频带变窄.

The streamwise velocity component at different vertical heights in wall turbulence was measured. Wavelet transform was employed to study the turbulent energy spectra, which indicates that the wavelet global spectrum results from the weighted average of Fourier spectrum based on wavelet scales. The wavelet transform with more vanishing moments can express the declining of turbulent spectrum; the local wavelet spectrum shows that the physical phenomena such as deforming or breakup of eddies have relations with the vertical position in boundary layer, and the energy-containing eddies exist in multi-scale form. Moreover, the size of these eddies is increasing with the measured points moving out of the wall. In the buffer region the small scale energy-containing eddies with higher frequency are excited. In outer region the maximal energy is concentrated on the low frequent large scale eddies and the frequent domain of energy-containing eddies becomes narrower.