Boundary layer separation

The separation of the boundary layer ( eng. Boundary layer separation ) - the phenomenon of detaching a layer of a viscous flow of liquid (gas) from the streamlined surface.

The point of detachment of the boundary layer is called the separation point. A reciprocating-vortex (not necessarily viscous) flow develops in the region between the detached boundary layer and the streamlined surface.

The separation of the boundary layer, for example, on the surface of the wing, part of the fuselage or another part of the aircraft actually leads to the fact that the body flows around a significantly different shape. This can lead to a significant change in the magnitude and direction of the aerodynamic forces ( lift , resistance to movement), change in the magnitude and direction of heat fluxes on the surface of the aircraft, etc., often worsening the aerodynamic characteristics of the apparatus, also applies to cars ^[1] , trains and so on. The energy of motion of the apparatus is also expended on maintaining the secondary flow that occurs after the separation. In this regard, the phenomenon of separation of the boundary layer is an adverse aerodynamic factor and in the design of aircraft, cars, trains, etc. measures are being taken to prevent separation.

The separation of the boundary layer occurs if the flow at the streamlined surface is inhibited by an unfavorable (increasing) pressure drop downstream. The separation can also be caused by shock waves and other disturbances falling on the boundary layer, the presence of kinks near the streamlined surface, etc.

The current lines in the flow around a car with a Kamm tail traced the separation of the boundary layer. Circular arrows show secondary flow area