Research On The Effect Of Double Volute Structure On Radial Force Of Centrifugal Pump Impeller

Due to the asymmetry of its structure and the change of flow rate during the actual operation of the centrifugal pump,the internal flow of the pump is not uniform,and uneven distribution of pressure on the circumferential position of the impeller may occur,resulting in radial force of the impeller,which makes the shaft subjected to alternating stress,resulting in directional deflection,causing vibration and noise of the pump.It is obvious that radial force is a key factor that causes the vibration noise of the water pump.In this paper,the type of SC125-100-200 A centrifugal pump is used as the original model.Under the condition of keeping the structure of the impeller unchanged,a double volute pressure water chamber is designed.The CFD numerical simulation method was used to compare the internal flow characteristics,pressure pulsation characteristics and radial force law of the two pumps.Firstly,according to the original model design parameters,a pressure chamber with a single volute structure is modified to design a pressurized chamber with a double volute structure.Three-dimensional constant-value simulation of the two pumps was conducted.The simulation data of the original model was compared with the experimental data.It was found that the head and efficiency of the simulation data were better than the experimental data and the errors were within acceptable limits,which shows that the numerical simulation results in this paper are credible.According to the analysis of the steady simulation results of the two schemes,it can be found that the static pressure of the single and double volute structures in the volute flow passage under different working conditions gradually increases from the inlet to the outlet of the volute.Under design conditions,the double volute structure has a larger external flow channel pressure than a single volute structure,while the internal flow channel double volute structure has a low pressure area at the initial position of the diaphragm,and then the pressure gradually increases.Under partial conditions,the pressure of the double volute pump in the inner flow channel is significantly lower than that of the single volute and the area is larger.Comparing the internal and external pressures of the double volute diaphragm,it can be seen that the pressure fluctuations on the outside of the diaphragm are relatively stable under the design conditions and low flow conditions,and the pressure is higher than the internal pressure of the diaphragm.The pressure inside the diaphragm fluctuates more violently.Comparing single and double volute speed vector diagrams,the speeds ofthe single and double volute from the inlet to the outlet of the volute gradually decrease under different working conditions,and the double volute structure is in the design of the casing and the partitions The positions are all high-speed zones symmetrical with respect to the center of the circle.The velocity gradients inside the double volute separators vary greatly,while the lateral flow velocity is lower and the velocity gradient changes less.The kinetic energy map mainly reflects the average characteristics of turbulent pulsation.The turbulent kinetic energy distributions of single and double volute structures are the best under design conditions.The turbulent kinetic energy of single and double volute casings strongly appears near the tongues and at the initial position of the double diaphragm.The distribution of turbulent kinetic energy is the worst under the condition of small flow.Under the condition of large flow,the turbulent kinetic energy of the single and double volute turbulent kinetic energy is larger at the outlet of the volute.In the constant calculation,the radial force of the impeller and the minimum radial force are all around the design condition.The larger the deviation from the design condition,the larger the radial force is.Then,on the basis of the simulation of the constant value,the unsteady numerical simulation of the centrifugal pumps of two different schemes was performed with the constant simulation results as the initial value of unsteady simulation calculation.Six monitoring points were set on both sides of the double volute separator to analyze the time and frequency domain characteristics of pressure pulsation around the separator.The results show that the pressure fluctuation amplitude at the outer monitoring points of the double volute pump diaphragm is smaller than that of the diaphragm as a whole,because the inner side of the diaphragm is greatly influenced by the fluid flow at the outlet of the impeller.Compared with single volute and double volute,under the design conditions,the pressure fluctuation of the initial position of the double volute casing is larger than that of the single volute,because the pressure of the added baffle fluid impacts the baffle plate.The pressure peaks and fluctuation amplitudes of double volutes in the middle of the separator and at the end of the separator are smaller than that of the single volute.Under periodical conditions,the periodical pressure fluctuation is not obvious under the design conditions.The periodicity of the double volute is more periodic than that of the single volute,and the pressure fluctuation is larger than that of the single volute.The pressure fluctuations are most severe under small flow conditions.Finally,for the rule of the radial force of the impeller,the calculation method of the radial force is introduced.In the unsteady numerical simulation calculation,sixpeaks appear in the single and double volute structures under different working conditions in the time domain.This is consistent with the number of blades of the pump under the design conditions and partial working conditions.The radial force of the pump and its fluctuation range are all smaller than those of the single volute pump..In the frequency domain diagram,the two major frequencies of the structure appear at the one-fold leaf frequency,and are rapidly attenuated at frequencies greater than the sub-frequency until there is almost no response at high frequencies.In this paper,the transient radial directions of the two structures are compared and analyzed.Under different working conditions,the radial direction of the single and double volute impellers is elliptical and the periodicity is obvious.Comparing single and double volute structures,the direction of the instantaneous radial force of the double volute is all around the origin of the coordinates,and the direction of the instantaneous radial force of the single volute is deviated from the origin of coordinates.From the analysis of the above-mentioned steady and unsteady radial forces,we can see that the double volute structure can effectively balance part of the radial force,which is of great significance for the centrifugal pump shock absorption and noise reduction.