An experimental investigation of free-surface structures in turbulent channel flow at low Reynolds numbers

grantor: University of TorontoFlow visualization using photochromic dye activation (PDA) and image processing was performed in a smooth, open channel to study the turbulence beneath the shearfree and waveless, gas-liquid interface. Experiments were done over a low-Reynolds number range of 800 to 2,400 based on liquid depth and a Froude number range of 0.25 to 0.32. Turbulence quantities obtained from statistical analysis of the instantaneous streamwise velocity profiles include the mean velocity distribution, probability density function, turbulence intensity, skewness and flatness factors and Reynolds stress. On the video recordings, coherent motions of large-scale free-surface structures were qualitatively observed, namely upwellings, downdrafts, spiral eddies and streamwise vortices. Visual counting of wall events showed that the scaling of their temporal frequency with the inner variables of viscous shear stress and viscosity improved with increasing Reynolds number, yielding average ejection and bursting periods of 39 and 119 for the highest Reynolds number, respectively.M.A.Sc