Abstract
Cavitational damage is very important for huge hydraulic structures exposed to high flow velocities. The most effective solution to avoid this damage is to mix air into the flow through an aerator device. The conventional method which is the physical model test is not sufficient to determine the air entrainment owing to scale effects caused by viscous forces. Computational fluid dynamic (CFD) method can allow simulating and analyzing the structures with real prototype dimensions by eliminating these scale effects. In this study, an outlet tunnel together with its aeration tunnels having 12 m diameter transformed from three derivation tunnels of a huge dam was analyzed using three-dimensional CFD model in real three dimensions. The scaled physical model results were also used to see the scale effects and to test validation of the numerical results. The aerodynamics of the aeration gallery and aeration tunnel were analyzed by two-phase (air–water) turbulent model, and the aeration performance of the system was tried to be improve with the help of CFD results. Three different designs for the aeration were analyzed and it was seen that the enhanced designs significantly increased the aeration performance of the system.
Highlights
Derivation tunnels are constructed to derive river flow even in flood condition from the construction area of the dams
Computational fluid dynamics (CFD) method has been widely used to determine the hydrodynamics of the flows in the hydraulic structures
The flow is supposed to be fully turbulent, but the viscous effects are dominant at low discharge for the physical model studies that the values are low
Summary
Derivation tunnels are constructed to derive river flow even in flood condition from the construction area of the dams. Dynamic similarity ensures two ways for incompressible flow: If there is no free surface, Reynolds numbers of model and prototype are equal. For the model tests including free surface, exact dynamic similarity is only achieved by equivalent Froude and Reynolds numbers. On the other hand, when considering air flow in the hydraulic model, the important parameters are the Reynolds and Mach numbers. In this case, the following relation can be obtained for compressible fluids. The compressibility effects of high-velocity air flow are generally neglected in the hydraulic model tests when using Froude number similarity. The physical model tests (Fig. 1) were performed with Froude numbers similarity with 1/40 scale (DSI Report 2013).
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