Resolving Viscous Forces in CFD

What is the method used by FLUENT to evaluate the viscous forces (breakdown) on wall BC?

Answer 1

If you are simulating a flat plate at zero angle of attack then all the viscous forces will be along X(streamwise direction) and all the pressure forces along Y (normal to wall). But  for an aerofoil, there is a local slope for the wall at every point so in the global coordinates the shear forces will have x and y components. At every local point along the wall the shear force will be tangential to it and pressure forces normal to it. Since the aerofoil, generally. has a curvature with varying slopes there will always be x and y components for both shear and pressure forces.

If you are trying to calculate using viscosity*du/dy (here y is local wall normal coordinate not global y). If you use global coordinates then there is a component of viscous forces from x direction as well not just y.

Carefully accounting for components of forces from different directions at every local point along the aerofoil and then integrating for the whole system will resolve any ambiguities.