How to set the grid for turbulent-boundary flow As many books and papers said, for the turbulent-boundary flow， The distance from the wall to the first cell center is set to satisfyat least y+ &le; 2, and there are approximately20â€"30 gridpoints within y+ < 100. (Ubaldo Cella, Arthur Rizzi. Sensitivity to Physical and Numerical Modeling in Navier-Stokes Simulations ) or

0.1&le; y+&le;0.5 for low Reynolds number model, 0.5&le; y+&le;1.0 for high Reynolds number model. (Tuncer ,Cebeci. Turbulence models and their application : efficient numerical methods with computer programs.) I have a question : Before the calculation, how can we get &tau;W for y+,since y+= y(&tau;W/&rho0.5/&nu;？ especially for compressible flow, &rho;,&nu;in y+= y(&tau;W/&rho^0.5/&nu; can't be taken as&rho;&infin;,&nu;&infin;,what hell can I do?

Usually, u should try some coarse mesh first and then try to refine the places where it needs. It also depends on the turbulence model you are using and the variables you want to get. You see, for a wing simulation, for some turbulence models you need to refine the mesh in the shear layer to obtain the aerodynamic coefficients. For other models, u should not to refine this region, because it may use some wall treatment. I hope it helps...