The time dependent flow over V- and U-groove riblets of different sizes

The flow over V-groove and U-groove riblets is examined computationally using a time dependent model of the viscous wall region. The flow at the upper bound of the computational domain (y+≂40) is described using a streamwise eddy model. Both drag neutral and drag reducing riblets are considered. Results suggest that the riblets limit the lateral spread of inrushes towards the wall and retain low momentum fluid in the riblet valleys, thereby effectively isolating much of the wall from such inrushes. The generation of intermittent secondary vortices within the riblet valleys also occurs; however, these appear to be both quite weak and fairly short-lived.