Numerical Investigation of Nozzle Jet Flow in a Pelton Microturbine

Abstract

The characterization of flow through Pelton hydro turbines allows the optimization of their operation and maximization of energy performance. The flow in the injector of Pelton turbines and in the free jet area (the area from the injector outlet surface to the runner bucket inlet surface) is influenced by several parameters: the geometry of injector components (nozzle and injector spear), the injector opening, and the turbine head. The parameters of the free jet flow (velocity distribution, pressure distribution, and jet spread) are reflected in the turbine efficiency. The research presented in this paper focuses on the numerical characterization of flow in the injector and the free jet of a Pelton microturbine. Three injector geometries were considered, with different nozzle diameters: 13.3 mm, 14.4 mm, and 16.3 mm. For each of these geometries, the flow was analyzed for five values of turbine head (H = 15 m, H = 20 m, H = 25 m, H = 30 m, H = 35 m) and six values of injector opening (S = 3 mm, S = 6 mm, S = 9 mm, S = 12 mm, S = 15 mm, S = 18 mm). The results of numerical simulations were used to plot injector flow-rate characteristics and injector force characteristics (the resultant force on the injector spear and the resultant force on the injector nozzle). The highest influence on the flow rate variation is given by the variation of turbine head, followed by the variation of the injector opening and the variation of the nozzle diameter. Increasing the nozzle diameter accentuates the variation of the flow rate versus the turbine head. The variation of axial velocity and pressure in the free jet is presented for four sections parallel to the outlet section of the injector. The injector openings that generate the highest values of velocity/pressure on the runner inlet surface are highlighted. The results allow optimization of functional parameters for increasing turbine efficiency and optimizing the design process of Pelton microturbines.