Flow separation occurs when the boundary layer travels far enough against an adverse pressure gradient that the speed of the boundary layer relative to the object falls almost to zero. The fluid flow becomes detached from the surface of the object, and instead takes the forms of eddies and vortices. In aerodynamics, flow separation can often result in increased drag, particularly pressure drag which is caused by the pressure differential between the front and rear surfaces of the object as it travels through the fluid. For this reason much effort and research has gone into the design of aerodynamic and hydrodynamic surfaces which delay flow separation and keep the local flow attached for as long as possible. Examples of this include the fur on a tennis ball, dimples on a golf ball, turbulators on a glider, which induce an early transition to turbulent flow regime; vortex generators on light aircraft, for controlling the separation pattern; and leading edge extensions for high angles of attack on the wings of aircraft such as the F/A-18 Hornet.
Boundary layer separation occurs when the portion of the boundary layer closest to the wall or leading edge reverses in flow direction. As a result, the overall boundary layer initially thickens suddenly and is then forced off the surface by the reversed flow at its bottom.
Read more about Flow Separation: Adverse Pressure Gradient, Influencing Parameters, Internal Separation, Effects of Boundary Layer Separation
Famous quotes containing the words flow and/or separation:
“Reminiscences, even extensive ones, do not always amount to an autobiography.... For autobiography has to do with time, with sequence and what makes up the continuous flow of life. Here, I am talking of a space, of moments and discontinuities. For even if months and years appear here, it is in the form they have in the moment of recollection. This strange form—it may be called fleeting or eternal—is in neither case the stuff that life is made of.”
—Walter Benjamin (1892–1940)
“I was the one who was working to destroy the one thing to which I was committed, that is, my relationship with Gilberte; I was doing so by creating, little by little and through the prolonged separation from my friend, not her indifference, but my own. It was toward a long and cruel suicide of the self within myself which loved Gilberte that I continuously set myself ...”
—Marcel Proust (1871–1922)