عنوان مقاله [English]
This paper describes in detail a new two-dimensional transient model for prediction of thermally stratified reservoir flow. Unlike many other reservoir models such as CE-QUAL-W2 and Mike-Reservoir, the present model does not employ the hydrostatic approximation. The full general orthogonal three-dimensional equations of motion, which are laterally averaged by Karpik and Raithby (1990) and produced a set of two-dimensional equations in the vertical plane, are used. Using an orthogonal boundary fitted mesh, the governing differential equations are rendered discretely by a finite volume technique. The resulting set of coupled difference equations for momentum, mass, and energy are solved by MAC method.
The previous studies were not accurate however, for example, the calculated underflow was predicted a thicker and slower than actually observed in the flume. Johnson suggested that these anomalous features of calculated flow were due to the fact of the model represented the sloping bottom by "stair steps" rather than employing a boundary fitted coordinate system. Another possible reason for differences that suggested by Karpik is due to the hydrostatic pressure approximation.
Karpik used a semi-implicit program developed by modified SIMPLE method which was not very successful in diffirent cases due to divergence, so an explicit MAC-type model is developed. The present model is tested in general and compared by Johnson's flume data. The results show the model is well able to predict the important features of density under-flow. But some numerical diffusions errors occur when we have changes in coordinate system, so in future studies this model with a more accurate scheme and more uniform grid would be perfect