Question

topic : boundary layer similarity

what is the functional dependence of the average friction coefficient, Cf?

Answer 1

The functional dependence of Avergae friction coefficient for a boundary layer is given by relation: Cf= [T/1/2*rho*u^2],where T is wall shear stress,rho is the density of fluid,u is the velocity of free stream.Or Cf=[(2/Re) * ∂u/∂y|_y=0] where ∂ represents the partial derivative of velocity which gives an idea of shear stress at the wall and Re represents the Reynolds number of fluid based on total length.

Also, ∂u/∂y|_y=0= f(x*, Re,dP/dx) where x* x-cordinate in direction of fluid flow and dP/dx is the pressure gradient required for fluid flow.

Hence functional relationship for C_f=[(2/Re) x f(x*,Re), where f represents some functional form.