Longitudinal surge oscillations in gallery-type surge chambers of hydropower systems: Novel partition-based modeling and mechanism analysis

Gallery-type surge chambers (GTSCs) are widely used in large hydropower stations. However, their high length-to-height ratios may induce longitudinal surge oscillations (LSOs) that cannot be captured by conventional lumped-parameter models. To address this limitation, a partition-based modeling framework is developed to simulate hydraulic transients and the longitudinal propagation of LSOs in GTSCs. The proposed model is benchmarked against the conventional lumped-parameter model. It is further used to investigate the coupled dynamics of throttling-orifice discharge and spatially distributed water-level oscillations under asymmetric turbine transients. Parametric analyses are conducted to quantify the effects of the overflow discharge coefficient m and the partition number N on LSO characteristics. The results show that wave propagation, reflection, and superposition within the GTSC produce localized surge extremes that cannot be captured by lumped-parameter modeling. In the studied case, the longitudinal difference in extreme surge levels reaches 1.30 m, indicating that conventional design approaches based on a uniform water-level assumption may underestimate local safety risks. The proposed model provides an efficient framework for capturing LSO dynamics and supports system-level assessment and design of hydropower systems equipped with GTSCs.