Water hammer investigation of the shut-down of a high-head hydropower plant at very high Reynolds number flows

Abstract

This paper investigates water hammer phenomena in a refurbished high-head hydropower plant (HPP) Perućica, Montenegro during shut-down of the entire plant (i.e., the simultaneous closure of the seven Pelton turbine units). An in-situ measuring campaign during a number of steady and unsteady conditions has been performed on the plant’s open channel, pressurized and tail race sub-systems with the primary goal of defining measures that will enable the achievement of the plant’s installed capacity. In-house software written in Visual Fortran and based on the method of characteristics (MOC) has been developed. The closure of the Pelton turbine distributors is modelled with the two-speed closing law. Dissipation torques in the turbine housing and shaft bearings are considered in the calculation of the Pelton turbine unit rotational speed change. Numerical results given for standard quasi-steady and convolution-based unsteady friction models are compared with the results of measurements at flows with very high initial Reynolds numbers (larger than 107). The developed numerical model shows good agreement with the results of site measurements. It is shown that the unsteady friction has a small impact on pressure histories in Perućica HPP.