Confinement and Bed‐Friction Effects in Shallow Turbulent Mixing Layers

Abstract

The transverse development of the turbulent mixing layers in an open channel flow of shallow water depth was investigated experimentally to study the confinement and bed‐friction effects. Mean and r.m.s. velocity profiles were obtained, using a hot‐film anemometer, at a number of cross sections downstream of a splitter plate between two streams of different velocities. In the confinement between the free surface and the channel bed, the transverse spreading rate of the shallow mixing layer was initially twice as large as the nominal rate for the free mixing layer. The spreading rate reduces with distance from the splitter plate under the stabilizing influence of bed‐friction, and diminishes to zero in the far field region when the bed‐friction number exceeds a critical value of about 0.09.