Transition in Oscillatory Flow Over Rough Beds

Abstract

Laser doppler anemometer measurements of turbulence intensity in oscillatory flow over rough beds are reported. The beds consisted of two grades of sand, gravel, and pebbles, and the measurements were made in an oscillatory flow water tunnel. Turbulence intensity was found to vary with phase, height above the bed, and Reynolds number. The measurements are compared with previous observations of transition to turbulence based on the distortion of dye traces. Various relationships that have been proposed for the conditions governing transition to turbulence are investigated, and suggestions are made for criteria for the initial onset of turbulence and for fully developed turbulence.