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[FAQ]

Known Parameters: density (rho), kinetic viscosity (mu), free stream velocity (U_inf), characteristic length scale (L), and the desired y plus (y+). Find: the first cell height (y). The Reynolds number is Re = rho * U_inf * L / mu. The skin friction coefficient C_f can be calculated from Re. For example, for flow on a plate, we have the following formula: C_f = 0.058*Re^(-0.2). For internal flows, we have: C_f = 0.079*Re^(-0.25), in which Re is based on pipe diameter. Use C_f to predict the wall shear stress tao_w: tao_w = 0.5*C_f * rho*U_inf^2. From tao_w compute the velocity U_tao: U_tao = sqrt(tao_w/rho) . Then, the first cell height can be calculated as: y = y+ * mu / (U_tao * rho).