Abstract: Flows past the inlets and outlets cause a significant part of the total head loss in the water transmission system of a pumped storage power plant, and its accurate calculation is needed in evaluation of the plant’s economic benefit. This paper uses numerical simulations to study the head loss coefficients of 14 types of side inlets and outlets. Using the multiple linear regression method, we formulate regression equations that can calculate the head loss coefficient, and examine its variations with the shape parameters of the inlets and outlets. The results show that the influence of these parameters on the loss coefficients is significant in the outflow condition while insignificant in the inflow condition. Under the outflow condition, a positive correlation occurs between the loss coefficient and the parameters－the length of the diffusion section, the distance between the middle pier retraction of the diffusion section, the horizontal diffusion angle, the vertical diffusion angle, and the ratio of the width of the side hole in the pier head of the diversion section, and the slope ratio of the reverse slope section－while a negative correlation occurs between the loss coefficient and the length of the adjustment section or the length of the anti-vortex beam section. The head loss coefficients calculated using the regression equations agree well with the calculations from numerical simulations. Application of our regression equations is a new way to calculate the head loss coefficients of side inlets and outlets.

Key words: side inlet and outlet, head loss coefficient, structural parameters, numerical simulation, regression equation