Flow separation

In aero- and hydrodynamics flow separation describes a flow condition in which the flow becomes detached from the wall. If excessive deceleration of the flow occurs (pressure increase), or if there is an abrupt change in the direction of the wall, the flow outside the boundary layer will no longer follow the direction of the wall but will become detached from it. Downstream of the point of separation, the boundary layer thickness increases considerably and local recirculation develops in the resulting dead water zones or areas of separation. Flow separation is associated with eddies and vortices and resultant flow losses.