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.