A fourth-order difference method is combined with the vorticity-vector potential formaulation in the generalized coordinate .Turbulent flows are computed in channels with the transverse riblet of convex or concave wall surface using the large eddy simulation technique with the dynamic subgrid scale model. As a result it is shown that turbulence is weakened by the concave transverse riblet and effect of drag reduction is found at the Reynolds number 8,000 and when the interval of the riblet corresponds to the length of the Tollmien-Schlichting wave. The reason is that the fluid moves toward the concave wall and the strengthening of the streamwise vorticity is protected.
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