Research On The Statistical Characteristics Of Scale To Scale Energy Transfer Of Wall Bounded Turbulence Based On LBM

For the reason that the scale-to-scale energy transfer characteristics of wall bounded turbulence exhibit strong inhomogeneous and anisotropy in three dimensional physical space,understanding the spatial distribution of energy scale-to-scale transfer is of great importance for the further exploring of energy transportation in physical space between different scales.Direct numerical simulation were performed at Reynolds number Re_?=18 0 by using lattice boltzmann method(LBM).The filter-space technique is used to obtain the scale-to-scale transport of kinetic energy.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 main conclusion is summarized as follows:1.The small energy flux structure account for the majority in number,and the distribution character shows that 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.Considering that the energy forward-scatter structure and backward-scatter structures tend to occur in pairs,further result shows that the energy flux structure pairs tend to be arranged side by side along the span direction.2.The comparation of the energy flux structures under different filter scales show that the structure under relatively small filtered scales tends to distributed far away frow the wall which in contrast with the large one whose structures tend to be attached to the wall.The conparation of the geometric characteristics exhibited that the energy flux structures volunme increased with the filtered scales,which was mainly caused by the increases of size in both streamwise and spanwise direction.Nevertheless with the filtered scales further increased,the streamwise contribution to the increases of volume apparently exceeded the spanwise one.From a statistical point of view,the large filtered scales of the structure is not only larger in total volume,but also narrower in spanwise and longer in streamwise direction.3.The comparation of the energy flux structures under different Reynolds numbers shows that the number fraction of the attached structures almost had no change,nevertheless,the volume fraction inreases significantly,and the energy transport process between the scales near the wall enhanced.The results of the geometric characteristics show that the scale exponent of l_x?l_y and l_z?l_y decreased,implying that the volume fraction inreases more comes from the increases of structure size in wall-normal direction.