Experiments on Unsteady Seperating Flow in an Open Channel

Abstract

Experiments on unsteady separating flow past a sudden expansion in an open channel are described. To simulate tidal flow the flow rate in the approach channel varied as a half-sine with time. Different visualization techniques to obtain an insight into the behaviour of the separating vortex in time and space were used. Laser-Doppler velocimetry (LDV) was employed to measure velocities and turbulence characteristics. The data obtained from the LDV-measurements was processed on a computer using the ensemble-averaging technique. Results at different flow rates of the visualization experiments, measured mean-velocity fields, and characteristics of the turbulence - such as intensities, Reynolds stresses and turbulence energy - are shown. Some examples of velocity power-spectra and statistical distributions are presented also. The experiments also provide information about the generation of turbulence related to the separation mechanism and that owing to boundary-layer instability.