Numerical Study on Generation and Transport of Total Dissolved Gas Supersaturation in Vortex Drop Shaft Spillway Tunnel
A vortex drop shaft spillway tunnel is an internal energy dissipator with a new type of inlet arrangement;owing to its simple structure,good energy dissipation,and lack of atomization at the outlet,it has attracted considerable interest for application in hydropower stations.However,total dissolved gas(TDG)supersaturation during its flood discharge is a critical issue that remains uninvestigated.In this study,the volume of fluid(VOF)method is used to simulate the fluid interface in the flood discharge process and the difference in flow patterns with and without the pressure plate is analyzed.Using Ansys Fluent combined with UDF to simulate the TDG saturation during the flood discharge process,the generation and transport model of the TDG in the vortex drop shaft spillway tunnel is established.The results show that the influence of the flood discharge velocity on the TDG concentration is significant.At a flood frequency of 0.02％(volume flow rate Q=503.36 m3/s),the TDG may exceed 140％above saturation and remain high downstream.By contrast,at a flood frequency of 0.5％(Q=248.39 m3/s),the maximum TDG can fall to approximately 130％and remain at approximately 120％downstream.Additionally,the sensitivity analysis of two key parameters affecting TDG in the established three-dimensional two-phase flow model:entrained gas volume fraction and initial bubble radius is carried out.It is found that the TDG increases with the increase of entrained gas volume fraction and the decrease of initial bubble radius,and the influence of entrained gas volume fraction is dominant.
Total dissolved gas supersaturationVortex drop shaft spillway tunnelTwo-phase flowNumerical simulation
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