Question

Which of these is true for an impermeable wall?

(a) \(\vec{V}=0\) above the surface

(b) \(\vec{V}=0\) at the surface

(c) \(\vec{V}.\vec{n}=0\) at the surface

(d) \(\vec{V}.\vec{n}=0\) above the surface

The question was asked by my college professor while I was bunking the class.

My query is from Boundary Conditions topic in chapter Boundary Conditions of Computational Fluid Dynamics

Answer 1

Correct choice is (c) \(\vec{V}.\vec{n}=0\) at the surface

The best explanation: For an impermeable wall, there can be no mass flow into or out of the wall. Therefore, the velocity at the surface must be completely tangential and its normal component will be zero (\(\vec{V}.\vec{n}=0\)).