Question

The displacement thickness is the distance by which, due to the presence of the boundary layer, the flow streamline is displaced.

(a) True

(b) False

I got this question by my college director while I was bunking the class.

My question is based upon Boundary Layer Properties topic in division Boundary Layers, Laminar & Turbulent Boundary Layers, Navier Stokes Solutions of Aerodynamics

Answer 1

Right answer is (a) True

The best explanation: Displacement thickness is one of the properties of boundary layer which is the distance by which the external streamline gets displaced due to the presence of the boundary layer.

Without the presence of boundary layer, which is the case of inviscid flow, the streamline would be straight and parallel to the flat surface. But due to the presence of boundary layer in real life scenario having viscous flow, the streamline is displaced.

The formula for the displacement thickness δ^* is given by:

δ^* = \(\int _0^{y1}\)(1 – \(\frac {ρu}{ρ_e u_e}\))dy