Author(s): Hamid Bashiri Atrabi; Takashi Hosoda; Hidekazu Shirai
Keywords: Air cavity advancing; Hydrostatic pressure; Mixed flows; Pressurized flow; Two-dimensional model
Abstract: In this study a two-dimensional (2D) depth averaged model is developed to simulate the transient flow from pressurized to free surface flow. This kind of flow can be occurred due to the rapid movement of a gate. The model is based on the hydrostatic pressure distribution in free surface region and the depth averaged continuity and momentum equations are used for the pressurized flow, free surface flow and the interfaces of both regions. In this model, the finite volume method (FVM) with the staggered grid system is used for flow calculations. The flood invasion analysis in flood plains is applied for the free surface region and the highly simplified marker and cell (HSMAC) method with pressure iteration procedure is applied for the pressurized part to recalculate the pressure and velocity. The numerical approach is an interface tracking and after finding the positions of interfaces, pressure drop is considered at the interfaces. To evaluate the numerical model, we conducted a few experiments in a square box based on the Benjamin flow with L-type gate using air and water as the two fluids. Initially, one part of the box was full of water under the pressurized condition and after removing the gate air was entered to the pressurized part. The main aim of this study is to simulate the water surface profile near the cavity front and also downstream of it. The two-dimensional numerical simulations are compared with the experimental data. The results showed good agreement and lead to the conclusion that the pressure drop at the interfaces is necessary.