The Scaling Law And Turbulent Characteristics In Turbulent Channel Flow

Channel turbulent flow is a kind of typical shear turbulent flow. The research of scaling law and turbulent characteristics in channel turbulent flow is the important reference for understanding complex turbulent flow mechanism, and it provides the basic theory of the study of turbulence structure and constitution of turbulence model. In recent years, there are many achievements in study of channel turbulent flow with improving of turbulent experiment technology and numerical simulation method, including the structure characteristics, scaling law, transport characteristics, scale characteristics, etc.In this study, based on the channel turbulent experiment database, we analyzed asymmetric channel turbulent flow used by Hilbert-Huang transform, and researched turbulent characteristics and transport characteristics through analysis of intermittent, coherent structure and momentum flux. Based on direct numerical simulation database, we analyzed the scaling law of viscometric functions in low Reynolds numbers symmetrical channel flow, especially the turbulent statistics scaling law and the Reynolds number effect in the near wall region. The main conclusions are as follows:(1) The logarithmic law is detected in the average frequency of the orders of Intrinsic Mode Functions which obtained by Empirical Mode Decomposition applied for streamwise and vertical velocity time series. And this law can be written as ωm=ω0η-m. The intermittency is intensified in small scales. Turbulent statistics depart from the Gaussian distribution at most of modes, except from 5th to 9th modes. The coherent structures reconstructed by 5% threshold have obvious time scale evolution from the smooth to rough surface. The Hilbert marginal spectrum and Fourier spectrum show the Kolmogorov-5/3 power law. The analysis of the momentum transport phenomena shows that there are local counter-gradient transport phenomena at certain modes while gradient transport occurs at other modes. The modes of coherent structures are consistent with the modes which contribute to the momentum transport principally including gradient and counter-gradient cases. This consequence was analyzed by Hilbert-Huang transform and wavelet analysis.(2) The research of full development channel flow of Newtonian fluids introduced into non-Newtonian viscometric functions. Based on low Reynolds number direct numerical simulation databases, the ratio of shear rate a+ and wall distance y+ with turbulent viscosity, apparent viscosity, the first and second normal stress are detected by vicomertic functions. Under different Reynolds number, the scaling law of different vicomertic functions is consistent. The first and second vicomertic functions present the dual scaling law and Reynolds number effect. These material functions, exhibiting a shear-thinning behavior, are fitted with the Carreau-type model. We reconstruct the new algebraic nonlinear power law constitutive equation which depended on the mean velocity gradient.