VELOCITY MEASUREMENTS CLOSE TO RIPPLED BEDS

K.I. Mahesha Ranasoma, J.F.A. Sleath

Abstract


Velocity measurements have been made with a Laser Doppler Anemometer in oscillatory flow over rippled beds. The ripples were naturally formed in an oscillating tray rig and then stabilised. Both large-scale mixing, repeatable from cycle to cycle, and turbulence were found to have a significant effect on the velocity profile. Large-scale mixing, which is associated with vortex formulation and ejection, was seen to dominate in the immediate vicinity of the bed but turbulent mixing appeared to be more important at large height. The variation in turbulence intensity with height was found to be qualitatively similar to that previously observed with threedimensional roughness in oscillatory flow. Time-mean velocities are not well predicted by existing theory. The present measurements show only two recirculating cells per ripple wavelength.

Keywords


ripples; velocity measurements

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