Estimation of the Minor-Loss at the Junction of a Headrace Tunnel and a Surge Tank with an Orifice

Abstract

The main goal of the investigation presented in this paper is to analyse influence of the orifice size on the water level oscillations in a surge tank arising during load rejection and water hammer in a hydropower plant. An approach to achieve it, which is adopted in this study, is to develop an adequate 1D model allowing a fast and reliable simulation of the hydraulic processes in the headrace tunnel and the surge tank. For such a model, estimation of the minor loss at the junction of the surge tank and the headrace tunnel has a crucial role. The calculated water level oscillations show a good agreement with the values measured in an existing surge tank with orifice. The results obtained with the same model for a set of different orifice diameters yield conclusions on the surge tank response in the case of modified orifice design.