Question

Displacement thickness in boundary layer theory represents:

• A. Thickness of wall
• B. Distance where velocity is zero
• C. Shift in outer inviscid flow due to boundary layer
• D. Distance of maximum shear

Hint:

Displacement thickness is an important concept in boundary layer theory because it quantifies how much the boundary layer alters the flow of fluid outside it.

Answer 1

The Correct Option is C

Displacement thickness is a measure of the reduction in the effective flow area due to the presence of the boundary layer. It represents the distance by which the outer inviscid flow is shifted because of the boundary layer, which accounts for the velocity deficit within the boundary layer. The displacement thickness is defined as the integral of \( 1 - \frac{u}{U} \), where \( u \) is the velocity at a given point and \( U \) is the free-stream velocity.