Numerical investigation of turbulent flow in Pelton turbine injector and jet quality

The injector of Pelton turbines plays an important role in energy conversion. The incoming high-pressure flow is displaced into decreasing areas in the injector, resulting in high kinetic energy of the flow. To maximize the kinetic energy at the outlet, the velocity distribution should be as uniform as possible. Non-uniform distributions lead to energy losses. Additional quality parameters of the emerging jet from the nozzle, besides the uniformity, are the surface deformation, the deviation, and the dispersion of the jet. A numerical flow study was carried out using the volume of fluid method for two phases with the free surface model to investigate the jet quality of two different injector designs. The flow separation at the edges of the seat ring is delicate, and fine-structured mesh with proper resolution of the boundary layers is required. The pressure in the air gap downstream of the separation point must be correctly predicted. The inflow to the nozzle is highly turbulent, effecting distortions of the surface of the free jet. These surface structures eventually can be simulated with detached eddy simulation (DES). The energy losses are evaluated, and plots of volume fraction and jet velocity profiles are provided. The 50˚-90° configuration shows better behavior with lesser energy losses and less impact of the wake flow of the needle support vanes on the surface deformation. The DES model showed a sharp water-air interface, while the Reynolds-averaged Navier-Stokes equation (RANS) simulation predicted a broader jet due to averaging eddies and fluctuations at the jet surface.