This animation shows the generation and lift-off of vortices due to an isolated hemispherical roughness element in the presence of an oscillatory boundary layer.
The external flow is imposed by a sinusoidally varying body force. The Reynolds number, based upon peak far-field velocity, hemisphere radius, and kinematic viscosity, is Re=200. The period of oscillation is 30 convective time units (R/U). The red iso-surfaces are the zero contours of lambda-2, following the vortex definition of Jeong and Hussain (JFM, 285 , 1995).
Slower version of this image.
Recent two-dimensional results.
Recent three-dimensional results.
Vorticity for the case T=40.
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Last update: December 30, 1998 (pff)