LES解析を用いた二次元翼の遠方後流の予測

抄録

The aim of this study was to investigate the vortex structure and the maximum vortex scale in the far wake of a two-dimensional NACA0012 airfoil. In order to estimate the maximum vortices scale, Large-Eddy Simulation (LES) for far wake of the airfoil was performed and integral scale of turbulence length for each of the three-dimension by using the cross-correlation coefficient of the flow velocity at two points in the wake was calculated. The condition of the flow around the airfoil was set to a Reynolds number of 4.0×10⁵ and an angle of attack of 9 degrees. The analysis area is 7C (C: chord length of the airfoil) in the flow direction from the trailing edge of the airfoil, 3C in the vertical direction of the flow direction and the grid resolution of (x⁺, y⁺, z⁺) = (40, 4, 10). The wake grid has a size that can capture eddies of 1mm in both the x and y directions. The vortex structure was observed by visualizing the second invariant of the gradient tensors. From this result, wake structures with various scales from the trailing edge to 2C or 3C had become longer in the flow direction at downstream were observed. The integral length was (x, y, z) = (0.056C, 0.025C, 0.017C) at 2C from the trailing edge and (x, y) = (0.083C, 0.039C) at 6C from it. Their aspect ratio on x/y of integral length was almost 2. As a result, the vortex structure generated from the airfoil was a structure that extended in the flow direction and integral length was twice long in the flow direction of the vertical direction.