THE TIME-DEPENDENT FLOW OVER V-GROOVE AND U-GROOVE RIBLETS OF DIFFERENT SIZES

The flow over V-groove and U-groove riblets is examined computationall y using a time dependent model of the viscous wall region. The how at the upper bound of the computational domain (y(+)similar or equal to 4 0) is described using a streamwise eddy model. Both drag neutral and d rag reducing riblets are considered. Results suggest that the riblets limit the lateral spread of inrushes towards the wall and retain low m omentum fluid in the riblet valleys, thereby effectively isolating muc h of the wall from such inrushes. The generation of intermittent secon dary vortices within the riblet valleys also occurs; however, these ap pear to be both quite weak and fairly short-lived.