Numerical Study On Internal Flow And Axial Force Of Nuclear Main Pump

For long-term working in high temperature and high pressure environment,axial force of impeller is up to thousands of Newton in nuclear main pump.This will affect the safe operation of the nuclear main pump.Setting balance holes and sealing rings on the impeller can effectively reduce the axial force of impeller.The balance holes connect the impeller flow channel with back chamber of the nuclear main pump,and the leakage fluid of balance hole will interfere with the fluid flow in the impeller passage to a certain extent.This leakage fluid will inference the flow field distribution and the energy performance of the nuclear main pump.In this paper,a nuclear main pump with an impeller drilled balance holes and set sealing rings is selected as the research object.The method of steady and unsteady numerical simulation are used to study the characteristics of internal flow and axial force of the nuclear main pump.Firstly,the steady flow numerical simulation of the nuclear main pump is carried out,and the results are compared with the experimental results.Under the rated condition,the error between simulation and experimental is small,which shows that the numerical method adopted in this paper has high reliability.The results of steady numerical simulation show that the leakage fluid of the balance hole and the front seal ring has obvious influence on the flow field of the inlet and the blade inlet under0.6Qopt;and the unsteady numerical simulation show that the pressure fluctuation in the nuclear main pump is mainly affected by the static and dynamic interference and the impeller rotation frequency;By changing the diameter of the balance hole,the influence of different diameter balance holes on the performance of the nuclear main pump and the flow field of the impeller is studied.The results show that with the increase of the balance hole's diameter,the nuclear main pump head and efficiency are reduced slightly,shaft power changes little,leakage of fluid on the impeller hub side fluid shock increases.Secondly,the main causes of axial force and the method of calculating axial force are introduced.By numerical method,the distribution law of fluid pressure in the pump chamber of the nuclear main pump is studied.The results show that the pressure of Front and back pump chambers increases along the direction of the radius of the impeller;The fluid flow coupling between front pump chamber and the impeller outletis strong,and the variation of fluid pressure at different circumferential positions is larger;The distribution of fluid pressure in the back pump chamber is more uniform than that in the front pump chamber,the pressure distribution of fluid in back pump chamber is like concentric circles.The distribution of pressure along the radial direction of the front and back pump chamber under 0.8~1.2Qopt is obtained by fitting radial dispersion point pressure.Finally,the influence of the balance holes and the gap on the pressure distribution and the axial force of the pump on the back pump chamber of the nuclear main pump is studied by changing the geometric parameters of the balance holes and the clearance of the sealing rings.The gap value and the diameter of the balance hole have a great influence on the pressure distribution and axial force of the pump chamber,while the gap width of sealing rings has little inference.With the increase of the clearance value,the fluid pressure entering the back pump chamber increases,increasing the fluid axial force acting on the rear cover,and increase the total axial force.The axial force of b=0.3mm is reduced by 9.552 k N when compared with b=1.0mm.With the increase of the clearance width,the fluid pressure entering the back pump chamber reduce,axial force on the back of impeller reduced,and total axial force is reduced.The axial force of l=26mm is reduced by 1.256 kN when compared with l=18mm.With the increase of the clearance width,the fluid pressure decreases near the balance hole,axial force on the back of impeller reduced,and total axial force is reduced.The axial force of d=5mm is reduced by 8.274 k N when compared with d=15mm.Through the above research,the nuclear main pump distribution of the whole flow field and flow characteristic of pump cavity pressure distribution are analyzed,the influence of the balance hole and the rear seal clearance on the axial force of the nuclear main pump are analyzed.The results have certain reference value for the optimization design of the nuclear main pump.