Optimal Design Of Screw-centrifugal Pump And Research On Flow-induced Vibration And Noise

The screw centrifugal pump is a single-blade impurity pump with excellent anti-clogging performance,wide high-efficiency area,and stable power.It is mainly used in the fields of food transportation,sewage treatment and papermaking.However,the problem of vibration noise during operation is relatively serious,and the design method is not yet mature.How to improve the hydraulic performance while mitigating vibration and noise has become an important topic in the study of screw centrifugal pumps.This paper studies the design methods,flow-induced vibration noise and performance optimization of screw centrifugal pumps through numerical simulation.The main research and innovations are as follows:(1)Proposed a new design method of screw-centrifugal pump based on CFturbo and SolidWorks.This method can significantly simplify the design process,and the performance of this pump is ideal.After the optimization of the screw centrifugal pump,the hydraulic efficiency at the design working point reaches 78.54%,and the hydraulic efficiency at the best working point reaches 81%.(2)Used CFX16.0 to calculate and analyze the internal flow field of the screw centrifugal pump.It is found that the spiral section of the impeller is mainly used as the power section.At low flow conditions,the high-pressure fluid in the volute will return to the spiral section of the impeller,seriously affecting the hydraulic and vibration noise performance of the pump.The pressure distribution in the volute is asymmetrical,and there is a return vortex in the area behind the blade exit edge,which causes energy loss and obvious vibration noise.As the flow rate increases,the return vortex shrinks and moves toward the diaphragm.(3)Analyzed the frequency response characteristics of pressure pulsation and radial force.It was found that the main peak of pressure pulsation is located at the leaf frequency,and the side peak is located at 2 to 4 times the leaf frequency.There is almost no pulsation signal at high frequencies.The pressure pulsation value at 1.0Q and 1.2Q operating conditions is small,and the pulsation amplitude at low flowconditions increases significantly.The radial force response characteristic is similar to pressure pulsation,and the pulsation signal is mainly concentrated in the low frequency band.Under the condition of 1.2Q,the radial force is the smallest,the smaller the flow rate,the greater the radial force.When the flow rate is reduced to0.6Q,the amplitude of the main peak of the radial force will increase to 8 times of the design condition point,and the secondary peak will increase to 5 times,which causes significant vibration noise.(4)Used LMS Virtual.Lab to calculate and analyze the internal sound field noise of the screw centrifugal pump.It is found that the leaf frequency is the main frequency of the internal sound field noise,and the maximum sound pressure value decreases as the frequency increases.From the perspective of the dipole noise of the volute,the sound pressure value at the design operating point is the smallest,and the sound pressure value at the partial operating condition increases,mainly manifested as the sound pressure value at the leaf frequency and 2 times the leaf frequency is unchanged,and the 3 times the leaf frequency The sound pressure at the location increased significantly.From the point of view of blade dipole noise,the distribution of high sound pressure area between 0.8 and 1.2Q operating conditions is quite different,but there is no obvious difference in sound pressure value.Dynamic and static interference and return flow are the main sources of internal acoustic field noise.The high sound pressure area at the dynamic flow and static interference position at large flow conditions is enlarged,and the high sound pressure area at the return flow position is reduced;,The high sound pressure area of the return position expands.(5)Calculated and analyzed the radiation noise of the external sound field based on the acoustic-vibration coupling method.It is found that the external sound field noise is broadband noise,and the main frequency of the sound power is the leaf frequency.The sound power at 1-7 times the leaf frequency shows a monotonous downward trend,and the sound power basically remains unchanged after 8 times the leaf frequency.The maximum sound pressure value of the external sound field is the lowest under the design conditions,and the maximum sound pressure value increases under the 0.8Q and 1.2Q conditions.0.8Q sound power is the weakest,the soundpower becomes stronger as the flow increases.The dynamic and static interference is the main cause of the noise outside the blade frequency.Backflow and dynamic and static interference are the main causes of the external sound field noise at 2 and 3times the leaf frequency.The noise is mainly radiated in the direction of the pump inlet,and the sound pressure value behind the pump is small.(6)Optimized the impeller in terms of hydraulic performance and flow-induced vibration and noise.In this paper,the outlet edge of the blade was cut into beveled edge and rounded edge,and it was found that the head is reduced after the outlet edge is cut,but the hydraulic efficiency is significantly improved.Among them,the efficiency of the impeller at the rounded exit side is 5% higher than that of the uncut impeller,but there is no noise reduction effect.The efficiency of the impeller at the oblique exit side is slightly lower than that of the rounded exit side.It is inferred that expanding the cutting area can achieve vibration and noise reduction,but it needs to pay attention to the amount of cutting.(7)Optimized the impeller in terms of dynamic balance performance to mitigate the vibration noise caused by the inertial force generated by the impeller at high speed.In this paper,SolidWorks Motion was used to calculate the dynamic unbalance mass and phase angle of the impeller in dry state,and then the unbalance is decomposed into different areas of the blade,and adjusted the thickness of the back surface of the blade by equal thickness and the end of the hub.In this paper,after two counterweights,the unbalance of the impeller is reduced to G6.3.