Numerical Research On Dynamic Equilibrium Process Of Balance Disc In Multistage Pump

Multistage centrifugal pump is a product that was widely and numerously used in various fields, at present, the imbalance of axial force is an important reason that causes the damage of multistage centrifugal pump. So the balance disc is widely used in multistage pump because of its simple structure, automatic balance performance, however, the performance of balance disc depends on its structure parameters. In views of this, at the basis of theoretical research, the balance disc-rotor system motion equation was combined and the dynamic equilibrium rules was simulated by MATLAB software, then analyzed the different structure parameters’ effect to the dynamic equilibrium rule of balance disc. According to the simulation result shows that the equilibrium value would be dependent on the structural parameters of the balance disc: any one of the face area, length, radial clearance, axial clearance increases, equilibrium value increases; But the equilibrium value would decrease as the length of the radial clearance increases. And the overshoot would be determined by the difference between the initial value of axial clearance and its inherent equilibrium value: the smaller the difference, the smaller the overshoot.At present, there are many theoretical researches on the clearance flow in balance disc,most of study is under the assumptions of laminar flow conditions, but the numerical study is not much, in order to understand the characteristics of flow in two clearances better and prove the feasibility of laminar flow hypothesis. The technology of dynamic mesh in the software of FLUENT is applied to simulate the dynamic equilibrium process of balance disc in DG155-67*5 multistage centrifugal pump successfully at the basis of theoretical research,and get the following conclusion:(1) The maximum Reynolds number in radial clearances is 1000, smaller than 1100,and the maximum Reynolds number in axial clearances is 1700, but the most Reynolds number are smaller than the critical Reynolds number. so the flow in two clearances can be considered as laminar flow.(2) The flow in two clearances was disturbed seriously by the velocity that was vertical to clearance in starting phase, and it gradually stabilizing after 0.0052 s, the vertical velocity fluctuation can be ignored, because it is too small. So the flow can be considered as laminar flow.(3) At the starting moment, the pressure of outlet in last stage impeller is smaller than the pressure in back cavity, so the fluid in balance disc flowed from back cavity to impeller.After a few seconds, the reversal flow in balance disc wouldn’t happen again, when the pump running after 0.0052 s, the pressure of outlet in last stage impeller meets the design value, the disturbance of balance disc is small, which can be ignored. so the flow in balance disc can beassumed as laminar.(4) It is verified the feasibility of laminar flow hypothesis inside two clearances by successfully using the technology of dynamic mesh.The research in this paper can supply a concise and effective method for the reasonable design of balance disc, and provide a specific theory method to solve the problems such as frequent grinding and leakage in the wor king process of balance disc. Eventually solve the problems of operation instability and short service life of multistage centrifugal pump in operations.