Study On The Influence Of Cavitation Flow On Energy Conversion Characteristics Of Nuclear Main Pump

In the nuclear power system,the nuclear main pump which is called the heart of the nuclear island is one of the power equipment of nuclear reactor coolant system and the primary pressure boundary of a circuit.Nuclear power plant primary loop SBLOCA and the heat trap loss accident are likely to cause the nuclear main pump cavitation,which lead to lower its head and efficiency,and cause overheating of reactor core.It has serious impact on the performance and safe operation of nuclear main pump when the cavitation is serious.In this paper,choose a model pump of nuclear main pump with independent design as the research object,through the numerical calculation,and combined with the test data research the internal cavitation flow characteristics o f nuclear main pump deeply.The main research contents and results are as follows :1.Effect of cavitation flow on energy transfer in nuclear main pump impeller.Through the variation of pressure and velocity on the streamlines,combined with the basic equation of the pump,the dynamic and hydrostatic head of the nuclear main pump under different cavitation conditions are studied.The results show that the energy of fluid of nuclear main pump is provided by posterior segment of impeller,and the energy of the fluid decreases gradually from the shroud to the hub.Cavitation interferes with the flow of liquid in the impeller,which leads to the relative velocity increases and the pressure decreases in cavitation region,and the work capacity of blades is almost 0 in bubble areas.At the same time,in non-cavitation region along with streamlines the dynamic head increases and the hydrostatic head decreases with the development of cavitation,and the decrease of the hydrostatic head is greater than the increase of the dynamic head,which results in the decrease of pump head and efficiency.In addition,in the cavitation region,with the development of cavitation,the sudden change of the dynamic and hydrostatic head increases,which increases the flow loss in the impeller and results in the decrease of pump head and efficiency moreover.2.Influence of cavitation on the performance of nuclear main pump.Four kinds of cavitation conditions are chosen,and the performance and internal flow field variation law of the nuclear main pump are obtained by comparison.The results show that the head,efficiency and power of the nuclear main pump have different sensitivity to the reduction of available net pos itive suction head.As the deepening of the cavitation,the change rate of the head is the largest,then is efficiency,and the change rate of power is the smallest.At the same time,the bubbles generated by cavitation changed the fluid state of the cavit ation region,so that the dynamic viscosity of the fluid decreased,resulting in the reduction of the turbulent dissipation rate of the cavitation region,and reduced the loss of the turbulent dissipation.3.Effect of blade inlet geometry on cavit ation flow characteristics of nuclear main pump.The cavitation simulation for four kinds of model pump with different blade inlet geometry is carried out,and the influence law of blade inlet geometry on the performance of nuclear main pump is obtained.The results show that: the blade inlet edge thinning,the crowding-out effect of blade inlet edge to the fluid is weakened,and the adaptability of blade on the changes of the inlet flow condition is improved,so as to reduce the flow loss at the inlet of t he blade and increase the efficiency.In addition,increasing the blade inlet edge fillet,intensifying of the blade inlet edge thinning degree,the cross section area of the inlet is increased and the velocity is reduced,which lead to increase of pressur e and the low pressure zone gradually moves towards the blade outlet.When cavitation occurs,the effect of bubbles on the flow of fluid at the inlet of the blade becomes smaller.At the same time,with the blade inlet edge thinning degree aggravate,blade inlet edge is closer to streamline,the impact generated by liquid flow around the blade head is reduced,and the minimum pressure of the suction surface near the inlet is increased.