Displacement thickness

Displacement thickness is a measure of boundary layer thickness. Displacement thickness is defined as the distance by which the boundary layer should be displaced to compensate for the reduction in flow rate on account of boundary layer formation. The concept of displacement thickness finds its application in the design of ducts and wind tunnels.

Momentum thickness

Momentum thickness is a measure of the boundary layer thickness. Momentum thickness is defined as the distance by which the boundary should be displaced to compensate for the reduction in momentum of the flowing fluid on account of boundary layer formation.