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Flow regime in dam's bottom outlet is divided in pressurized flow and free surface flow by the gate located for discharge control. Down stream tunnel involves high velocity Multi component Air –water flow studied by mathematical model. In this research work, we used Finite volume mixture two phase flow model. Because of high Reynolds number, standard two equations k-e turbulence model was used. Model was verified by backward-facing step flow and results have been compared with experiments founded by Durst and Schmitt. Air demand ratio has been determined as function of Froude number at contracted section. Flow patterns have been compared at two categories of slug & stratified flows, Air mean concentration profile has been obtained at down stream tunnel. Comparison of flow pattern at two case with and without of aeration was investigated. Pressure drop behind of the gate and formation of vortex flow after the gate section have been discussed. Measurement of flow discharge and determination of contraction coefficient of the gate was outlined.

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In the present study a quasi 2-D numerical model is developed for calculating air concentration distribution in rapid flows. The model solves air continuity equation (convection diffusion equation) in the whole flow domain. This solution is then coupled with calculations of the free surface in which air content in the flow is also considered. To verify the model, its results are compared with an analytical solution as well as a 2-D, numerical model and close agreement was achieved. The model results were also compared with experimental data. This comparison showed that the decrease in air concentration near the channel bed in an aerated flow could be well predicted by the model. The present simple numerical model could therefore be used for engineering purposes.

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This paper describes a numerical model and its finite element implementation that used to compute the cavitation effects on

seismic behavior of concrete dam and reservoir systems. The system is composed of two sub-systems, namely, the reservoir and

the dam. The water is considered as bilinear compressible and inviscid and the equation of motion of fluid domain is expressed

in terms of the pressure variable alone. A bilinear state equation is used to model the pressure–density relationship of a cavitated

fluid. A standard displacement finite element formulation is used for the structure. The Structural damping of the dam material

and the radiation damping of the water and damping from foundation soil and banks have been incorporated in the analysis. The

solution of the coupled system is accomplished by solving the two sub-systems separately with the interaction effects at the damreservoir

interface enforced by a developed iterative scheme. The developed method is validated by testing it against problem for

which, there is existing solution and the effects of cavitation on dynamic response of Konya gravity dam and Morrow Point arch

dam subjected to the first 6 s of the May 1940 El-Centro, California earthquake, is considered. Obtained results show that impact

forces caused by cavitation have a small effect on the dynamic response of dam-reservoir system.