湍流边界层外区超大尺度相干结构相位平均波形

用IFA300恒温式热线风速仪和X形二分量热线探针精细测量了风洞中平板湍流边界层不同法向位置的瞬时流向、法向速度分量的时间序列信号。通过对不同速度分量进行子波变换，得到了近壁区和外边界区流向和法向脉动速度分量的分尺度湍动能随尺度的分布，在外边界区发现流向脉动速度和法向脉动速度的能量最大尺度随法向坐标远离壁面增大，相干结构的平均猝发周期也相应增加，说明在外区存在超大尺度的相干结构。采用条件采样和相位平均技术，提取了近壁区和外边界区能量最大尺度相干结构流向及法向速度的喷射和扫掠的条件相位平均波形，发现流向和法向脉动速度及雷诺应力喷射和扫掠事件的条件相位波形较近壁区都发生了改变。雷诺应力负的幅值显著降低，雷诺应力表现为正负交替的波动现象。

Phase-averaging waveforms of superstructures in outer layer of turbulent boundary layer

An experimental investigation of the turbulent boundary layer was conducted in a wind tunnel with IFA300 constant temperature anemometer. The simultaneous time series of the streamwise velocity component and the normal velocity component at different wall-normal positions in the turbulent boundary layer were finely measured by a double-sensor X hot-wire probe. The distributions of the turbulence kinetic energy along with the scale were obtained in the near-wall region and the outer region of the turbulent boundary layer through wavelet transform on different velocity components. In the outer region of the turbulent boundary layer, the maximum energy scale and the average burst period of the coherent structure gradually increased. Large-scale vortical structure appeared in the outer region of the turbulent boundary layer. The conditional phase-averaging waveforms of the ejection and sweep events at the maximum energy scale of the coherent structure were extracted by the conditional phase-averaging technique in the near-wall region and the outer region of the turbulent boundary layer. The waveforms of ejection and sweep events in the outer region of the turbulent boundary layer were different from the waveforms in the near-wall region. The amplitude of negative Reynolds shear stress was reduced. The conditional phase-averaging waveforms of Reynolds shear stress presented positive and negative fluctuations.