Question

Which of these statements is correct?

(a) Inertia forces dominate in the flow far from the wall

(b) Viscous forces dominate in the flow far from the wall

(c) Inertia forces are small in the flow far from the wall

(d) Viscous forces are large in the flow near the wall

The question was asked during an interview.

This intriguing question originated from Turbulent Boundary Layer in section Turbulence Modelling of Computational Fluid Dynamics

Answer 1

Right option is (a) Inertia forces dominate in the flow far from the wall

To explain: As the flow of a fluid near the wall moves away from the wall, the Reynolds number of the flow increases accounting to the increase in the distance. This leads to high inertial forces and low viscous forces.