Experiments and computations on unsteady separating flow in an expanding flume

An unsteady, separating, flume flow with a free surface was investigated with a physical model and a numerical model. To simulate tidal flow, the prescribed flow rate at the inflow boundary was a half-period sine function of time. Velocities and wave heights were measured by a laser Doppler velocimeter and a wave-height meter in a straight open channel with a sudden widening and a nonreflective outlet. Distributions of depth-averaged velocities at different times were obtained. Numerical simulation of this flow was carried out using a computer program of second-order accuracy. The development of the recirculation region in course of time was well simulated, and the observed splitting of the main eddy in a later phase and the secondary eddy in the concave corner were reproduced. The computational results are markedly influenced by the boundary conditions at closed boundaries and the eddy viscosity applied.