| Due to the continuous increase in global demand for new energy electricity,this field is facing unprecedented challenges.Improving the scale and efficiency of existing energy conversion and developing new available energy sources are two different directions.The distribution of hydropower in China is uneven,and there are significant regional differences in economic development levels.In recent years,while continuously constructing conventional large and medium-sized mixed flow and axial flow hydropower stations,the use of large Pelton turbines to develop hydropower resources in areas with large drops,unsuitable construction of large reservoirs and dams,and relatively underdeveloped regional economy and transportation has become a new solution.The Pelton turbine is mainly composed of a water distribution ring pipe,nozzle,and runner,which has advantages such as simple structure,reliable operation,high efficiency and energy conservation,and strong adaptability to head changes.However,the research of Pelton turbines still faces some challenges,such as improving unit efficiency,optimizing impeller materials,and analyzing hydraulic characteristics.Further research and exploration are needed.This article simulates the internal flow of a six nozzle Pelton turbine,analyzes the causes of various hydraulic losses during operation,explores ways to eliminate and reduce losses,and provides scientific basis for optimizing the design of a multi nozzle impulse turbine.The specific research content and conclusions are as follows:1.Analyze the flow characteristics inside the water supply mechanism,and analyze the response relationship between different nozzle stroke and working head and the loss of the water supply mechanism;Analyze the influence of the internal flow state of the water supply mechanism on the free jet of the nozzle,and provide a detailed analysis of the deformation of the free jet.Research has shown that the hydraulic loss of the water supply mechanism of the six nozzle Pelton turbine mainly occurs at the nozzle,which is mainly caused by the flow separation vortex inside the bifurcated pipe and the vortex at the tail of the baffle.When the water head remains constant,the hydraulic loss of the nozzle decreases with the increase of stroke;At the same stroke,the hydraulic loss of the nozzle has little effect on the change of water head.2.Accurately capturing the characteristics of gas-liquid two-phase flow using VOF models,analyze the influence of stroke and speed on the efficiency of nozzle impact water turbines,reveal the mechanism of free jet affecting the efficiency of water turbines at different speeds through the vector triangle rule,and determine the main cause of hydraulic losses generated inside the runner by analyzing the internal flow field of the runner under stable operating conditions.Research has shown that when the working head and runner speed remain constant,as the nozzle stroke increases,the torque and input power of the six nozzle Pelton turbine runner decrease,and the efficiency first increases and then decreases.At a certain stroke,the highest efficiency can be achieved.When the working head and stroke remain constant,as the rotational speed of the runner increases,the torque of the runner gradually decreases,and the output power and efficiency first increase and then decrease.At a certain speed,the highest efficiency can be achieved.The reason is that the magnitude and direction of the combined force on the bucket of the Pelton turbine are different.Through vector triangle analysis,it can be found that the direction of the combined force is perpendicular to the bucket at a certain speed,and at this time,the efficiency of the turbine is the highest.The flow diversion inside the runner,the impact of the bucket outflow on the back of the next bucket,and the collision of water flows inside the bucket can all affect the output and efficiency of the hydraulic turbine.3.The efficiency of the nozzle was calculated under different combinations of nozzle angles and nozzle needle angles,and the optimal fitting angle to improve nozzle efficiency was determined.The entire basin of the hydraulic turbine with the optimal fitting angle nozzle was calculated and analyzed to determine whether it effectively improved the overall efficiency of the six nozzle impact turbine.The results show that the change in nozzle angle has no significant impact on the efficiency of the nozzle,while the change in nozzle angle will significantly affect the efficiency of the nozzle.The efficiency of the β/α=90°/55° nozzle in various flow rates has been significantly improved compared to the β/α=85°/55° nozzle,with an average efficiency improvement of 0.34%;Introducing a β/α=90°/55° nozzle into the entire basin of a six nozzle Pelton turbine for calculation,with an improvement range of 0.2%-0.4%. |
