明渠挟沙水流双层积分模式的双曲性分析
摘要
Recently we developed a physically enhanced double layer-averaged model for open-channel sediment-laden flow, which properly incorporates inter-layer interactions, sediment transport and morphological evolution. Yet it is hard to solve the whole set of governing equations of the two layers as a single system, the governing equations for each layer are cast into a non-homogeneous hyperbolic system, whilst the inter-layer interactions are represented as source terms as they are generally negligible when compared to inertia and gravitation. The two reduced-order hyperbolic systems of the governing equations for the two layers are solved separately and simultaneously. The performance of the model has been demonstrated for series of observed datasets. However, it remains to be revealed if the hyperbolicity is preserved. The present study analyzes and compares the eigenvalues of the governing equations when cast into a single system and two reduced-order hyperbolic systems respectively. As applied to typical stratified sediment-laden flows concerning dam-break floods over erodible sediment beds and reservoir turbidity currents, the model can preserve hyperbolicity and thus avoid Kelvin-Helmholtz instability although appreciable discrepancies of the eigenvalues of single system and two reduced-order hyperbolic systems are discernible. Computational tests for reservoir turbidity currents reveal that an excessive clear-outflow would keep the turbidity current from being spoiled, and also is conducive to improve sediment flushing efficiency and mitigate reservoir sedimentation.