Journal of Fluid Mechanics



Direct numerical simulation of turbulent flow over riblets


Haecheon  Choi , Parviz  Moin  and John  Kim 
Center for Turbulence Research, Stanford University, Stanford, CA 94305 and NASA Ames Research Center, Moffett Field, CA 94035, USA

Article author query
choi h   [Google Scholar] 
moin p   [Google Scholar] 
kim j   [Google Scholar] 
 

Abstract

Direct numerical simulations of turbulent flows over riblet-mounted surfaces are performed to educe the mechanism of drag reduction by riblets. The computed drag on the riblet surfaces is in good agreement with the existing experimental data. The mean-velocity profiles show upward and downward shifts in the log–law for drag-decreasing and drag-increasing cases, respectively. Turbulence statistics above the riblets are computed and compared with those above a flat plate. Differences in the mean-velocity profile and turbulence quantities are found to be limited to the inner region of the boundary layer. Velocity and vorticity fluctuations as well as the Reynolds shear stresses above the riblets are reduced in drag-reducing configurations. Quadrant analysis indicates that riblets mitigate the positive Reynolds-shear-stress-producing events in drag-reducing configurations. From examination of the instantaneous flow fields, a drag reduction mechanism by riblets is proposed: riblets with small spacings reduce viscous drag by restricting the location of the streamwise vortices above the wetted surface such that only a limited area of the riblets is exposed to the downwash of high-speed fluid that the vortices induce.

(Published Online April 26 2006)
(Received July 28 1992)
(Revised January 28 1993)



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