THE MEASUREMENT OF PARTIAL-DERIVATIVE-U PARTIAL-DERIVATIVE-Y IN A TURBULENT BOUNDARY-LAYER OVER A RIBLET SURFACE/

Statistics of partial derivative u/partial derivative y have been meas ured in a turbulent boundary layer over either a smooth wall or a ribl et surface using parallel hot wires. Over the riblets, the mean square value of partial derivative u/partial derivative y (normalised with s mooth wall variables) is smaller than over the smooth wall; the differ ence increases as the distance to the wall decreases. Also this differ ence is larger when the riblets operate in a drag-augmenting mode, The se changes would reflect changes in the near-wall turbulence structure . Furthermore, on the basis that partial derivative u/partial derivati ve y is a major contributor to the spanwise vorticity, the results ind icate that, relative to the smooth wall, the mean square spanwise vort icity is reduced near a riblet surface. (C) 1997 Elsevier Science Inc.