Modification of the shell type trifurcation shape for penstock design in a hydraulic plant by numerical simulations

The branching of pipes is commonly used for fluid distribution in penstock of hydro-power plants to reduce construction cost. A trifurcation allows flow of water to provide three turbines operating at the same time, and it is usually designed for uniform distribution of discharge rate and minimum hydraulic loss. A symmetric trifurcation not considered fluid dynamics occasionally may make unequal power production of each hydro turbine and its severe fluctuation. The paper focuses on the cause of fluctuating power production and suggests a solution for stable operation by numerical simulations. The discharge rate distribution for existing and modified shapes of the trifurcation has been investigated by steady state computations, and quasi-steady state calculations have been carried out in order to find the cause of the flow fluctuations in the penstock for rated plant discharge (Q_t = 153.66 m³/s). In addition, the time dependent flow structures and the head losses in the penstock have been compared for the existing and modified trifurcation shapes, and it is also verified that the fluctuating power production can be reduced significantly with modified trifurcation. (paper)