Turbulent boundary layers have been manipulated successfully using passive devices called BLADES (boundary-layer alteration devices) leading to net drag reduction. Measurements of various turbulence quantities including intermittency have led to the identification of some of the mechanisms involved in skin-friction reduction. Velocity and vorticity fluctuations associated with oncoming large scales are inhibited significantly by the manipulator blades and the vorticity shed in their wake. The manipulated boundary layers exhibit a reduced intermittency in the outer part of the layer. The effects of manipulation relax with downstream distance and the boundary layer returns toward normal conditions after 100 or 150 boundary-layer thicknesses.
Mechanisms leading to net drag reduction in manipulated turbulent boundary layers
AIAA Journal ; 28
01.02.1990
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Englisch