I'm working on a flow simulation project analyzing the shear stresses imparted to the bottom of a flow chamber and am wondering which method to use for the flow simulation. The simulations I've run up till now have been using an inlet boundary condition with a volume flow and an outlet boundary condition of atmospheric pressure. I was recently introduced to the idea of using an internal fan to simulate flow instead. Should I use a fan or keep working with boundary conditions? Will they affect my shear stress values or other surface goals differently?