Simulation Study On Fish Strike Damage In Tubular Pump Based With Fish-shape Particle Tracking Method

Low head cross flow pump is the core power component of large pump station,which directly affects the efficient and stable operation of the system.In recent years,our country has focused on the South-to-north water diversion,river diversion and One Belt and One Road large pump groups,most of which use low-head pump device.However,it is not friendly to fish in the process of operation,and a large number of fish impingement with flowing parts lead to damage or death.In order to reduce the impact damage of fish through the pump,this paper studied the impact damage characteristics of fish through the through-flow pump,analyzed the changes in the speed,drag force and impact force of fish during the impact between fish and blade,obtained the impact force threshold of fish through the pump and the thickness of the leading edge of fish and blade L/d=1.4～2,calculated the impact probability of fish through the pump and the impact force distribution characteristics of fish.It can provide reference for optimization design of fish-friendly hydraulic machinery.The main research work carried out in this paper and the main research results are as follows:(1)Based on the CFD-DEM coupling method,modify the coupling interface code to optimize the drag calculation model.Based on the drag-force model calculation method of non-spherical particles,the method further considers that there are multiple grids in the fish-shaped particles in the simulation.The flow field velocity of multiple points around the centroid of the fish-shaped particles is selected to carry out vector average.The average velocity of the fluid in multiple grids is used to interpolate the fluid velocity of the flow field in the particle,which can obtain more accurate slip velocity of the particle and the flow field,and improve the calculation accuracy of drag force.(2)Taking the simplified plate impact on fish as the starting point of numerical simulation,the effects of impact velocity,blade leading edge Angle,the ratio of fish length to blade leading edge thickness L/d on the motion behavior and mechanical damage of fish body impact on blade were analyzed.The results show that the impact damage caused by the fish body collision is related to the impact force on the fish body.Reducing the blade leading edge Angle,decreasing the impact velocity of the fish body and increasing the blade leading edge thickness can reduce the impact force between the fish body and the blade leading edge to reduce the stress damage of the fish body.The extreme force values during the impact between the fish body and the leading edge of the blade under different conditions were statistically analyzed and compared with the Amaral fish impact test results.It was concluded that the impact mortality threshold of the fish body with L/d=1.4～2=2443N.The simulated statistics were in good agreement with the fish mortality obtained from the fish strike test.(3)The over-pump damage and motion force of fish with different flow parts,different impact sites of fish body and different impact points of the leading edge of blades under the design conditions of the cross-flow pump were studied.The results show that the average impact force is the largest and the impact damage is the most serious when the fish body passes through the impeller component,the movement trajectory of the fish body passes through the guide vane component has the least change,and the average impact force is the least and the damage is the least.The survival rate of fish impinged on impeller parts under L/d=1.4 was 66.7%.The survival rate of fish passing through guide blade and bulb body parts is close to 100%.Impeller part is the most important part that causes damage and death of fish,and the impact force between fish body and leading edge of blade near the rim is the largest.The damage of the fish body with different L/d under the design condition of the initial impeller scheme cross flow pump was analyzed,and the impact probability and impact force extremum of the fish body through all the flow parts were statistically analyzed.The results showed that: With the increase of L/d,the probability of collision between fish body and all through-flow parts of the transversal pump increases,and the average impact force between fish body and all through-flow parts increases,among which the impact force of fish body with L/d=5.6 exceeding 2443 N accounts for the largest proportion in impeller parts,and the damage of fish body is the most serious.(4)The influence of different impeller design schemes on fish impingement damage under the design conditions of cross-flow pump is analyzed.The extreme force of the fish through the pump and the impact probability of the fish through the pump in different schemes are statistically analyzed.The results show that the impact probability of the fish colliding with different throughflow components is basically the same when the number of blades and the running condition of the through-flow pump are the same.In the four schemes of impeller optimization design,the average impact force caused by impeller collision with fish body is the largest and the damage of fish body is the most serious in the scheme of optimal efficiency.In the optimal scheme,the average impact force caused by impingers colliding with fish body is minimum,and the damage of fish body is relatively minimum.In the scheme with optimal efficiency,41.7% of the fish impact forces were less than 2443 N,and 66.6% of the fish impact forces were less than 2443 N in the scheme with optimal performance.The optimal design of blade can reduce the impact force between fish and the leading edge of impeller blade and thus reduce the impact damage of fish through impeller components.(5)The influence of the change of the running condition of the cross-flow pump on the impact damage characteristics of fish was analyzed.The statistical results of different impeller design schemes and different conditions of the intersecting pump show that: with the increase of the flow rate of the intersecting pump,the probability of impinging between the fish body and the impeller decreases,and the average value of impinging force increases,and the crossing performance of the intersecting pump is stronger under the condition of large flow rate.With the increase of the speed of the transversal pump,the probability of the fish body colliding with the impeller parts increases,the impact force becomes larger,and the impact damage to the fish body is aggravated.The lower speed of the transversal pump is more fish friendly.