Study on Hydraulic Fluctuations of Tailrace Tunnel Considering Downstream Channel Open-Channel Flow Disturbance
In addition to free-surface-pressurized flow phenomenon caused by the transition process,the tailwater channel fluctuation has an important impact on the stability of the long water transmission system.This study investi-gates the influence of downstream tailwater fluctuations on flow regime transition and unit performance using VOF mod-eling in open channels.The results reveal that the pressure pulsations in the tailwater tunnel behind the regulating well are mainly caused by the combined effect of the regulating well and downstream waves,exhibiting periodic oscillations.The pressure regulating well acts as a wave attenuator and effectively eliminates more than 95%of low-frequency pressure pulsations caused by waves originating from downstream.Under the sudden changes in downstream water level,the pres-sure pulsations transition from jet-induced large fluctuations to downstream wave-dominated smooth oscillations.Pulsa-tions caused by downstream waves have limited transmission to the runner area and are significantly influenced by the reg-ulating chamber.However,certain pulsation frequencies induced by jets,such as 0.820 3 Hz,can effectively impact the runner outlet and retain 67.2%of the pulsation amplitude,thereby influencing the performance of the runner.
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