Numerical And Experimental Investigations On The Unsteady Flow Characteristics And Induced Radial Force Of Single Blade Centrifugal Pumps

Single blade centrifugal pumps are special centrifugal pumps with only one large wrap angle blade and have the biggest cross section of the impeller flow channel.These pumps exhibit the best non-clogging performance and suitable for pumping medium with long fibers and large particles which are widely used.However,the impeller of single blade centrifugal pumps is a non-axisymmetrical,and the pressure fluctuations are strong and the radial force caused by the hydraulic imbalance is very large during the pump operation.To improve the stability of single blade centrifugal pumps,the unsteady flow characteristics of the pump and the induced hydraulic radial force have been studied.This work was financially supported by the National Science&Technology Support Program of China（No.2011BAF14B01）,Natural Science Fundation of Jiangsu province（No.20150508）and Research Project of the Graduate Research Funding Project of Jiangsu Province,“Single Channel Pump Design and Analysis of Internal Flow Characteristics”（No.KYLX₁043）and other projects.The main research work and innovative achievements are as follow:1.The velocity and pressure distribution of the single blade centrifugal pump were analyzed by numerical simulation and then the pump performance was obtained by experiment and verified the accuracy of the numerical simulation.The numerical results show that there are obvious flow separation and low speed areas in the single blade centrifugal pump,and the pressure distribution is circumferential asymmetry.The Q-H curve drops steeply and compared with ordinary centrifugal pumps,the efficiency of single blade centrifugal pump is lower.The hydraulic loss model of a single-blade centrifugal pump impeller was established,which revealed that the main reason for the low efficiency of the single-blade centrifugal pump is a large dissipation loss.Further analysis of the influence of blade outlet angle and blade wrap angle on the pump performance shows that the H,P and efficiency of the single blade centrifugal pump increase with the increase of the blade outlet angle.However,due to the effect of flow slip in the impeller,the change is no longer significant after the blade outlet angle increases to 18°;H increases with the increase of the blade wrap angle,and the Q-H curve becomes steep,the efficiency of the pump also increases with the increase of the blade wrap angle,but the high efficiency zone becomes narrower.2.The effect of the volute on the pressure fluctuations of single blade centrifugal pump was analysed by transient numerical simulation.The results show that the dominant frequency of the pressure fluctuations in spiral volute and circular volute is the impeller rotational frequency,however,there is not obvious frequency characteristics in impeller without volute and its amplitude of the pressure fluctuations is one order of magnitude lower than those in spiral volute and circular volute.The pressure fluctuations in single blade centrifugal pump are mainly caused by the rotor-stator interaction of the impeller and the volute.The pressure fluctuations in the volute are mainly affected by the interaction between the potential flow at the outlet of the impeller and the wall of the volute.Comparing the pressure fluctuations in the pump with different flow rates,it was found that it was aggravated by the severe flow separation at the lower flow rate conditions.The influences of different blade outlet angles and different blade wrap angles on pressure fluctuations were also analyzed.It was shown that the pressure fluctuations of a single blade centrifugal pump increases with the increase of the blade outlet angle,however,it decreases with the blade wrap angle.3.The high-frequency pressure sensor was used to measure pressure fluctuations on the volute and the front chamber of the volute.The results show that the pressure fluctuations in the volute is gradually weakened from the volute tongue along the rotation direction of the impeller,and the pressure fluctuations intensity is the smallest at the design flow rate condition.The frequency spectrum of pressure fluctuations at all flow rates are consistent with the numerical simulation results.The dominant frequency is the impeller rotational frequency.However,the experimental results have broadband pressure fluctuation signals in the range of 5 f_n.The pressure fluctuations intensity of the volute decreases significantly with the decrease of the rotational speed,but it does not completely correspond to the similar conversion of the rotational speed.The higher the rotational speed is,the stronger rotor stator interation is,and the stronger the periodicity is.On the other hand,the pressure fluctuations become more complicated and the periodicity becomes weaker at low flow rate.The pressure of the front chamber also fluctuates periodically,the dminant frequency characteristic is not obvious as the volute,and the rotor stator interation weakened in the front chamber.The pressure fluctuations predicted by numerical simulation were similar to those obtained by experiment.The time history of the pressure fluctuations at the design flow rate in the numerical simulation and experiment basically overlapped,and the qualitative agreement of the pressurefluctuations obtained by CFD numerical calculation and experiment was extremely high.4.The effect of the volute on the impeller radial force were analysed by transient numerical simulation.The radial force of the impeller fluctuates with the rotation of the impeller,and impeller radial force is the largest when the spiral volute is used,and the radial force is the smallest without volute.The impeller radial force curve is distorted circle and the center of the circle deviates from the origin point.The generation mechanism of the radial force for a single blade centrifugal impeller was revealed.The radial force acting on the impeller is mainly caused by the pressure difference between the pressure surface and suction surface.The rotor stator interation between the impeller and the volute is the main reason for the fluctuation of the radial force.The rotational speed has little influence on the radial force coefficient.The radial force of the impeller increases with the increase of the flow rate when the circular volute is used,however,when the spiral volute is used,the radial force increases with the flow increases in the range of 150°-330°,and the radial force is the largest at the low flow rate in the other areas.The influence of blade outlet angles,blade wrap angles and eccentricity of the single blade centrifugal impeller on radial force were analyzed.It was shown that the radial force increased with the increase of the blade outlet angle,but it decreases with the increase of blade wrap angle.And the influence of the eccentricity of the single blade centrifugal impeller on the radial force weaker than the ordinary centrifugal pump.The impeller center of rotation was the first time proposed that impeller eccentricity was adopted to balance the impeller radial force.The mean value of the eccentrical impeller radial force reduced 17%at the design flow rate,and it reduced 12.5%at high flow rate,and it also reduced 6%at low flow rate.At the same time,based on the simulation of ADAMS,the eccentricity of the impeller gravity center was adopted to balance the impeller radial force,and shows that it can effectively reduce the radial force of the single blade centrifugal impeller.A hydraulic radial force test bench for a single blade centrifugal pump was set up.The hydraulic radial force of a single blade centrifugal pump was measured using a miniature load cell and Hall sensor.The hydraulic radial force of the two impellers fluctuates with the rotation of the impeller.The radial force dominant frequency is the impeller rotational frequency.The radial force changed with the rotation of the impeller is a distorted circular which is deviated from the origin point.The radial force experimental results are basically consistent with the numerical simulation.5.A vibration experiment bench for a single blade centrifugal pump was set up.The non-contact high-frequency eddy current sensor was used to measure the transient displacement of the impeller wear ring.The radial displacement of the volute was measured by installing an acceleration sensor in the volute.The experimental results show that the instantaneous displacement trajectory of the impeller wear ring is a distorted ellipse.The displacement of the wear ring increases sharply at the 0.2Q_d,and it decreases with the flow rate increases,but the changes become not obvious after it close to the design flow rate.The displacement increases with the increase of the rotational speed,and the maximum displacement variation law is consistent with the radial force variation law with the rotational speed.The radial vibration of the volute increases with the flow rate increases,but the change is not significant.The radial vibration of the volute increases rapidly with the increase of the rotational speed.The RMS of the radial vibration acceleration of the volute is approximately proportional to the square of the rotational speed.