Two Phase Flow Analysis And Loss Evaluation Of Hydraulic Turbine

The residual pressure energy in industrial process is usually recovered by hydraulic turbine,so the hydraulic turbine is the core energy-saving equipment decided to develop in recent years.At present,the commonly used type of hydraulic turbine in China is pump reversing hydraulic turbine.Because the pump reverse hydraulic turbine is designed and manufactured under the condition of pump forward rotation,the efficiency of reverse operation is low,and the high efficiency operation area is narrow,so it can not keep stable working state.The hydraulic turbine has the advantages of high efficiency and stable performance.Therefore,this paper selects a hydraulic turbine for analysis.In the actual process of residual pressure energy recovery,the working fluid is usually gas-liquid two-phase,so it is necessary for the turbine to operate stably in the gas-liquid two-phase condition.In order to study the flow rule and loss mechanism of turbine under two-phase condition and improve turbine efficiency,Euler Eulerian particle two-phase model and SST are used in this paper The K-? turbulence model is used to simulate and analyze a hydraulic turbine.The external characteristics of the turbine under different operating conditions are explored.The flow mechanism of two-phase working fluid in the turbine is analyzed.The variation law of two-phase entropy production with void fraction is obtained.The relationship between entropy generation distribution and two-phase flow is explored.The results show that the turbine efficiency is about 92%under pure liquid condition,and the turbine efficiency and output power decrease obviously with the increase of gas holdup.Through the analysis of different types of entropy generation,it is obvious that the increase of turbulent entropy production with void fraction leads to more serious adverse flow,which is the main factor for the increase of entropy production loss.The entropy production loss in the volute is very small,and there is a certain impact loss in the guide vane,while the runner and draft tube are the main components of entropy generation.The entropy production distribution map is analyzed and compared with the gas phase distribution diagram and streamline diagram It is found that the entropy production is higher at 10%and 90%of the blade height,and the high entropy production area is formed in the vortex area of the runner and the high void fraction area of the suction surface of the blade,which is concentrated at the head and tail of the blade The vortices between the runner blades caused the passage blockage,resulting in the disorder of flow pattern and the formation of high entropy production area.Under the condition of small flow rate,the effect of gas volume fraction on the pressure loss is gradually increased under the design condition and large flow rate condition.The high gas content region appears in the impeller,and the entropy production changes with the gas content obviously.The gas accumulation area in the center of draft tube is more obvious with the increase of gas holdup,which is also a high entropy production area.