Experimental Studies On The Scales Of Coherent Structures, The Expressions And Characteristic Parameters Of SL Scaling Law For Different Statistic Quantities In Open-channel Turbulent Boundary Layer

For understanding the mechanism of turbulent boundary layer better, coherent structures and the parameter of SL scaling law were researched with experimental methods. We proved some conclusions made by others using different methods and found some new phenomenon. Then some explanations were given out.First, characteristic scales of coherent structures in turbulent boundary layer, such as the wall inclination angles of streaks and shear layers, the spanwise scale of streamwise streaks and the evolution of vortices, were measured by PIV with the continuous wavelet analysis and the traditional statistic method. The present results were compared with the previous results in literatures.Next, SL scaling law at seperate scales were obtained by discrete wavelet analysis. Pulsatile quantities such as u', v'and dv'/dx were considered respectively. Here, two forms of scaling law based on SL scaling law were used to fit the experimental curves and nice results were obtained.Then, in the outer region of turbulent boundary layer where the gradient of mean velocity was low, we measured the energy dissipation rate by PIV. The analysis was conducted under two hypotheses respectively, the homogeneous and isotropic turbulence hypothesis and the axisymmetric turbulence hypothesis. Based on the two hypotheses,β, the hierarchy similarity parameters defined in SL scaling law of energy dissipation rate were obtained in the whole flow field respectively, and we find that the two results were almost the same to each other. Then hierarchy similarity parameters at different heights from the wall were calculated based on axisymmetric turbulence hypothesis. From the results, we conjecture that the gradient of time-averaged velocity would influenceβ.Last, using PIV, we measured the velocity field in the near wall region of turbulent boundary layer, and got several characteristic scales. In the inertial range, we calculated the hierarchy similarity parameters of the energy dissipation rate on different heights.βwas not varied as we thought before and showed complex fluctuations . Furthermore in the region of viscous sublayer and buffer layer, on several heightsβexceeded 1. So we considered that the organization structure of turbulence would be the main reason of howβchanged, not the velocity gradient.