Momentum Balance Model of Flow Field with Pseudo-Shock

The length of a pseudo-shock was estimated with a new momentum balance model. In the model, it is presumed that there is no wall friction in the region of the pseudo-shock. Inflow conditions are specified at a boundary sufficiently upstream of the pseudo-shock. The outflow boundary condition is applied with, for example, specified pressure or choking. The outflow impulse function is balanced with the inflow impulse function, the wall friction upstream of the pseudo-shock, and the reaction force from the wall. The starting position of the pseudo-shock is determined through balance of the forces in this model. The model was applied to several kinds of flow fields, for example, straight ducts with and without a backward-facing step, and divergent ducts. The model was also applied to the diffuser of an ejector-jet, in which two gases flowed in parallel. The calculated results agreed well with the experimental results. The starting position of the pseudo-shock was primarily dominated by the reaction force in the divergent duct. Several features of the pseudo-shock were explained with the present model.

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