Research On Hydraulic Balance Of Screw Centrifugal Pump

The screw centrifugal pump is a special and novel pump with unique structure.Its unique spiral centrifugal impeller can take full advantage of the spiral pump and centrifugal pump.As a sewage pump,its efficiency is higher than that of the swirling impurity pump and centrifugal impurity pump.In addition,compared with the general centrifugal pump,the spiral centrifugal pump has the advantages of good non-blocking performance,good lossless,good inhalation performance and so on.However,due to the asymmetrical structure,there is a large eccentricity,which generates a large centrifugal force.At the same time,the radial force of the impeller is also relatively large,which makes the vibration problem of the rotor system more serious.For the hydraulic balance of screw centrifugal pumps,the main work done in this paper and the main conclusions obtained are as follows:(1)The design method of spiral centrifugal pump is briefly introduced.With the specific design parameters,the spiral centrifugal pump impeller is hydraulically designed using the grid mesh conformal transformation method,and the spiral centrifugal pump is three-dimensionally modeled using Pro/E5.0.The Gaussian curvature of the blade was detected.It was found that the Gaussian curvature of the blade on the hub side at the inlet of the impeller changes rapidly,and the smoothness of the blade is lower here.(2)The steady and transient simulation of the internal flow field of the screw centrifugal pump was performed using CFX15.0.The pressure distribution and velocity distribution on the radial section,axial section and surface of impeller during steady state calculation were analyzed.It is found that there is a phenomenon of detachment at the inlet of the impeller.There are vortices in the larger range of impeller passages and significant secondary flow in the volute,which affects the energy conversion of fluid in the volute and is not conducive to the improvement of pump efficiency.With the increase of the blade wrap angle and the impeller radius,the pressure on the surface of the impeller gradually increases,and there is a low pressure region at the root of the blade working face.Because of the asymmetry of the impeller structure,the pressure distribution on the surface of the impeller is also asymmetric,which makes the radial force of the impeller larger.(3)The commonly used radial force calculation method is introduced.The radial force distribution of the impeller and the pressure pulsation inside the volute are analyzed during the transient calculation.It is found that the radial force of the impeller changes periodically under different flow conditions,and the cycle is the same as the time it takes for the impeller to rotate.Under design conditions,the maximum radial force of impeller is relatively small,and the farther away from the design condition,the greater the maximum radial force is.The direction of radial force maximum value is opposite under small flow condition and large flow condition.The radial force is composed of constant and pulsating quantities,and as the frequency increases,the pulsation peak gradually decreases.The main frequency of the pressure pulsation is the shaft frequency,and the peak of the pressure pulsation appears at the main frequency and its frequency multiplication,and it is mainly the low frequency pulsation.(4)The critical speed,mode shape and transient response of the screw centrifugal pump were calculated and analyzed using the professional rotor dynamics analysis software SAMCEF Rotor based on the finite element method.It is found that as the order increases,the vortex frequency of the rotor system also gradually increases.The rotor is a rigid rotor,and resonance does not occur under the design conditions,and the first four modes of the rotor system are all bending deformations.When the effect of radial force on the transient response of the rotor system is considered,the frequency component of the radial force will be reflected in the vibration of the rotor.(5)The vibration of the rotor system under different blade exit edge cutting patterns and the effect of impeller weight on hydraulic balance performance of screw centrifugal pump were analyzed.It is found that with the increase of the cutting angle of the blade outlet edge,the radial force of the impeller and the vibration displacement are gradually reduced,and the cutting angle has an optimal value.The unbalanced type of the rotor system is dynamic unbalance.After balancing the impeller with the double-sided balancing method,it is found that under dry and wet conditions,the vibration of the rotor system and the hydraulic balance performance are improved.