Study On Flow Instability Under Nuclear Main Coolant Pump Reversal Conditions

This paper is mainly devoted to the main coolant pump which is one of the most important parts of the first loop of the nuclear reactor.It plays an important role in transporting the coolant and ensuring the smooth discharge of the core heat.Since there is no anti-reversal mechanism in the main coolant pump of the 3^rd generation of nuclear power technology,the main pump has the possibility of reversal running in the conditions of broken shaft,power outage,starting one by one and so on.On the one hand,the reversal main pump causes the instability of the flow and,on the other hand,it also has a negative effect on the force on the pump shaft.Therefore,it is necessary to study the reversal condition of the pump.In this paper,a miniature model of the 3^rd generation nuclear power technology AP1000 main coolant pump is studied.Firstly,to study the blade surface boundary layer shedding and vortex formation,the cause of vortex shedding on a hydrofoil is discussed with the point of view of the flow angle of attack and the effect of pressure diffuser.It is found that vortex-shedding phenomenon is obvious when both the flow angle of attack and the pressure diffuser effect exist simultaneously.The vortex shedding frequency is proportional to the angle of attack after a certain angle of attack.All kinds of reversing conditions are considered,and theoretical deduction is performed to complete the flow parameters.Unsteady numerical simulation is conducted for different reversal conditions of the main coolant pump.The external characteristic parameters under various conditions are given,and the instabilities of the internal flow of different geometry components are analyzed in detail.It is found that the frequency had an impact in the entire flow,and the impeller and inlet pipe are also affected by the guide vanes.The pressure pulsation in the impeller is characterized by beat waves which is considered to produce system oscillation and noise.During the reversal process,the impeller blades will form a closed flow space with the guide vanes,leading to change the flow direction and form the vortex in the impeller,which affects the downstream flow.All components in reversal pump have the energy loss,with a basic stable proportion in each case,in which the impeller accounted for the largest proportion in energy losses and the volute ranks the smallest.There are pro-vanes and retro-vanes in the guide vane.The fluid passing through the retro-vanes will produce longer vortex.Swirls are formed on the concave of the guide vane,which occupy 20%to 80%of the flow space.Moreover,the radial force and axial force of the pump are calculated.The radial force was unevenly distributed in the direction perpendicular to the inflow pipe of the volute.The axial force is periodically changed by 2 times the frequency.The direction of axial force points to the inlet tube and it is mainly affected by the frequency of the impeller.The axial force also decreases with the mass flow rate and the rotating speed decreasing in different conditions.