Experimental and numerical investigation on head losses of a complex throttled surge tank for refined hydropower plant simulation

Abstract

For a large hydropower plant (HPP) with long-distance tunnels, a surge tank needs to be installed to ensure the safety of the HPP during hydraulic transients (i.e., load changes in hydro-turbines). The head losses of the surge tank and its throttle are necessary conditions and evidence of the hydraulic design and one-dimensional (1D) simulation of the HPP. This study is conducted to investigate the head losses of a complex throttled surge tank for a refined 1D HPP simulation. Based on model experiments and computational fluid dynamics (CFD) simulations, the statistical laws of the total head loss coefficient are determined, and the dynamic refined formulas for the resistance and discharge coefficients are proposed. Finally, the proposed discharge coefficients are applied to refined 1D HPP simulations and compared with the traditional discharge coefficient. It is preliminarily revealed that the discharge coefficient undergoes a step change under load rejection and a continuous hump-shaped change under increasing loads. The water level results calculated using the proposed discharge coefficient differ by 1.69 m, i.e., 3.65% of the total height of the surge tank, compared with using the traditional discharge coefficient. This study can facilitate the understanding of hydraulic design and HPP optimization.