Effect of level of inflow turbulence on the spatial development of a shallow mixing layer in an open channel

Z Cheng; G Constantinescu

The effect of level of inflow turbulence on the spatial development of a shallow mixing layer is discussed based on high-resolution eddy-resolving numerical simulations. The shallow mixing layer develops between two parallel streams with a bulk velocity ratio of 2.3, which are initially separated by a thin splitter plate. The flow develops in a long, constant depth channel with a flat smooth bed. The Reynolds number defined with the flow depth, D, and mean bulk velocity of the two streams is 15,500. The length of the channel is 400D, which is twice as long as the flume used in an experiment conducted with similar flow conditions. The numerical predictions are compared with experimental results over the upstream part of the channel. The effect of inflow turbulence is studied by comparing two extreme cases. In the first case, the two streams contain resolved velocity fluctuations corresponding to fully-developed turbulent flow. In the second case, the incoming flow contains no resolved velocity fluctuations (steady inflow condition at the two stream inlets with the same mean velocity profile). The streamwise evolution of key mixing layer variables (e.g. mixing layer shift and width) and the effect of level of inflow turbulence on flow structure are analyzed. While the width variation with the distance from the origin is similar in the two cases, significant differences are observed in the region where the coherence of the mixing layer eddies is the largest. Downstream of the transition to the equilibrium regime starts, the lateral shift of the mixing layer is nearly identical for the two cases.

Effect of level of inflow turbulence on the spatial development of a shallow mixing layer in an open channel

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