Research On The Fish Damage Mechanisms In Francis Runner And Optimization Of Fish Survival Probability

The development of hydropower projects in China will inevitably have a negative impact on the ecological performance of fish,and even causes the extinction of some precious fish species,thus affecting the species diversity and the development of fisheries.Turbine equipment in hydropower stations is one of the main causes of fish casualty.Fish are mainly damaged from the strike of rotating runner blade with high speed,pressure,shear and cavitation when passing the turbine flow passage.Therefore,it is of great significance to explore the method of analysing fish casualty probability caused by various mechanisms and optimizing fish-friendly turbine runner blades.Based on computational fluid dynamics(CFD)theory,the probability of fish struck the Francis runner blade was analyzed and the runner fish-friendly optimization was carried out.The major work and verdicts are as follows:(1)Study on the fish damage mechanism in Francis runner and determination of quantitative analysis method.A method for calculating fish strike mortality in Francis runner was established by combining CFD analysis,the blade-strike model and the fitting model of radial basis function(RBF)neural network.Then,based on the fish friendly threshold for pressure,pressure change rate and shear strain rate,a method for calculating the pressure and shear damage probability of fish was established.2(2)Fish casualty probability analysis in the runner.Based on the method of calculating the probability of fish being damaged by various factors,the law between the probability of fish injury caused by these mechanisms and the working conditions was analyzed.From the results it can be seen that the fish damage probability caused by blade strike,pressure,shear and pressure gradient in the runner is positively correlated with the discharge.Comparing the probability of fish being damaged by each mechanism under the same discharge condition,it can be concluded that the probability of injury and death caused by the impact of runner blade is much higher than that caused by other factors.Therefore,the impact of blade is mainly taken into consideration in the fish friendly optimization of Francis turbine.(3)The influence of the number of runner blades on the casualty probability of fish.By decreasing the number of runner blades and optimizing the distribution law of blade wrap angle,two improved runners with 11 and 13 blades were obtained.The damage probability of fish caused by blade strike,low pressure,high pressure gradient and strong shear stress in the two improved runners was analyzed and compared with the original runner.From the results it can be seen that the improved runners can effectively reduce the damage probability of fish caused by various factors.Finally,by synthesizing fish ecological performance and hydraulic performance of two improved runners,the improved runner with 13 blades is selected as the final scheme.The research methods and contents can provide valuable reference for the fish friendly optimization of Francis turbine.