STRUCTURE STATISTICS OF SCALE TO SCALE ENERGY TRANSFER OF WALL TURBULENCE BASED ON LBM

For the reason that the scale-to-scale energy transfer characteristics of wall bounded turbulence exhibit strong anisotropy in three dimensional physical space, understanding the spatial distribution of energy scale-to-scale transfer is of great importance for the further construction of high-fidelity anisotropic large eddy simulation models. Direct numerical simulation were performed at Reynolds number $Re_{\tau } =180$ by using lattice Boltzmann method (LBM). In comparison with the open source channel flow turbulence database, both the mean velocity and turbulent variables, such as Reynolds stress and velocity fluctuations, agree well with the results of Kim et al. (1987) and Moser et al. (2015). The ability and validity of LBM on simulating turbulent channel flow were verified. The filter-space technique is used to obtain the scale-to-scale transport of kinetic energy, and the statistical results show that the backward scatter and forward scatter contributions to the SGS dissipation were comparable. Combined with the novel structure identification method, the distribution and geometry properties of the energy flux structure is quantitatively investigated by the clustering methodology. The results show that small scale structures account for the majority in number, and the volume probability density distribution presents a -4/5 power law. The structures can further be divided into wall attached structures and wall detached structures according to their minimal distance to the wall. In spite of the relatively small number fraction, the attached structure accounts for most of volume fraction, which shows that most of the attached structures are large scale structures. Further statistics of the attached structures exhibit that the size of the structure has a certain power law relationship, indicating that the scale-to-scale energy transport structure also has the self similarity of the attached eddy hypothesis which proposed by Townsend. The forward and backward energy flux structure pairs tend to be arranged side by side along the span direction.