A Random Choice Scheme for Transient Mixed Flows

A novel numerical model for describing highly transient mixed flows is presented based on the Preissmann slot approach. To overcome the spurious oscillation problems caused by this approach, a numerical scheme named "random choice method"(RCM), in which flow variables of the next time level are obtained by picking a local Riemann solution state at random, is applied herein. Three numerical tests are performed to verify the ability of the proposed model in simulating from single flows to mixed flows. The results show that the RCM gives sharper shock resolutions as compared with the Godunov-type scheme, which causes the smearing of discontinuities. The proposed model can eliminate the numerical oscillations under flow conditions of switching from free-surface flow to pressurized flow, because of its unconditional stability. On further analysis of the experimental verifications, a hybrid method is presented to improve the performance of RCM in the smooth (nonuniform) parts of the flow.