| The impeller of a single blade centrifugal pump has only one blade,and the impeller channel has a large flow area.The single blade centrifugal pump is not easy to be blocked and has high reliability when conveying sewage containing solid particles and long fibers.However,the performance and reliable operation of the pump are greatly affected due to the weakening of the single blade’s ability to control fluid and the obvious unsteady flow in the pump.In order to reveal the operating characteristics and internal flow law of single blade centrifugal pump,the influence laws of key geometric parameters of blade on external characteristics,internal flow field distribution,transient pressure characteristics and cavitation characteristics of the single blade centrifugal pump were studied by combining theoretical analysis,numerical calculation and experimental research.The internal flow characteristics of single blade centrifugal pump were further analyzed by PIV particle imaging velocity measurement technology.The research conclusions provide theoretical guidance for the hydraulic optimization and design of single blade centrifugal pumps,and provide support for China to achieve the goal of "double carbon".The main research contents and creative achievements of this thesis are as follows:1.The research scheme for the blade inlet edge position and the blade inlet angle was formulated.The influence of the blade inlet edge position and the blade inlet angle on the external characteristics,impeller outlet loss and the internal flow field of the single blade centrifugal pump was analyzed,and the reliability of the numerical calculation method was verified through experiments.It is found that the appropriate extension of the blade inlet edge to the pump inlet can increase the pump head by 0.6m-2.0m and the pump efficiency by 3.0%-5.8%.At the same time,the extension of the blade inlet edge can reduce the collision loss at the impeller outlet and reduce the load on the blade middle streamline near the blade inlet.The blade inlet angle has little effect on the head and efficiency,but the optimal selection of the blade inlet angle is conducive to improving the pressure value at the inlet of the blade suction surface,reducing the fluid collision loss at the impeller outlet,and improving the ability of the impeller to convert fluid kinetic energy into pressure energy.2.Based on the whole fluid domain numerical calculation model of a single blade centrifugal pump,the effects of blade inlet edge position and blade inlet angle on the transient pressure fluctuation characteristics in single blade centrifugal pump were analyzed by using an unsteady numerical calculation.It is found that the extension of the blade inlet edge towards the pump inlet is conducive to reducing the transient pressure fluctuation intensity of the blade pressure surface and suction surface close to the blade inlet,which can be reduced by 16.5% and 22.7% respectively,but will increase the transient pressure fluctuation intensity at the impeller outlet,which can be increased by 29.1% at most.At the same time,with the extension of the blade inlet edge,the peak of the transient pressure curve at the impeller outlet gradually flattens,the peak amplitude decreases,and the random pressure fluctuation decreases.The intensity of the transient pressure fluctuation in the volute increases with the extension of the blade inlet edge,up to 45.3%.At the same time,the transient pressure amplitude increases,the random pressure fluctuation decreases,and the main frequency amplitude roughly increases.The blade inlet angle affects the shape of the peak and trough of the transient pressure curve,and affects whether random pressure fluctuations and secondary peaks occur at the impeller outlet and in the volute.In addition,the flow rate and rotating speed have a significant effect on the transient pressure fluctuation characteristics at the impeller outlet and in the volute.3.The transient pressure test scheme of single blade centrifugal pump was designed.The transient pressure of single blade centrifugal pump under different working conditions was tested on the external characteristic test setup using high-frequency pressure sensors and other test instruments.It is found that the transient pressure of the monitoring point far from the tongue fluctuates periodically within the operating flow range,while the transient pressure of the monitoring point near the tongue fluctuates disorderly.The calculated value of transient pressure at all monitoring points is greater than the test value.Under the condition of large flow rate,the variation trend of the calculated value is consistent with that of the test value.Because of the asymmetry of the volute structure and the decline of the control ability of the single blade to small flow rate fluid,the coincidence degree of the change trend between the calculated value and the test value under the small flow rate condition is reduced.4.Taking the single phase numerical calculation results without cavitation as the initial values,the influence of blade inlet edge position and blade inlet angle on the cavitation characteristics of the single blade centrifugal pump was studied,and the reliability of the numerical calculation method was verified by cavitation test on the external characteristics test setup.It is found that the cavitation performance curves of pumps with different blade inlet edge position are similar,and the bubble volume in the pump tends to decrease with the increase of blade inlet edge extension.Under the fracture condition,the pump with the largest extension of the blade inlet edge has the largest load on the blade middle streamline,but within the first third of the blade middle streamline,the blade load of all impellers is 0 or negative.The pump with blade inlet angle increasing from front shroud to rear shroud along axial streamline has small bubble volume and relatively large blade load.5.The PIV test platform was designed and built,and the characteristics of internal flow field in the single blade centrifugal pump were studied by means of PIV particle imaging velocity measurement technology.It is found that the fluid on the middle cross section of the impeller basically rotates with the impeller,and there is an obvious velocity dividing line at the junction of the impeller and the spiral casing.Under the action of centrifugal force,the fluid spreads from the center of the impeller to the surrounding,and the single blade plays the role of helical propulsion.The flow at the tongue is obviously impacted,and the streamline is not smooth.The position of the blade outlet has a significant effect on the flow field of the spiral casing.The number of vortices in the section near the front and rear shroud in the spiral casing is more than that in the middle section,and the vortex strength is stronger and the average velocity is higher.Due to the boundary layer,vortices with high intensity appear on the wall of the spiral casing.As the flow rate decreases,the number and intensity of vortices in the spiral casing decreases,and the average velocity in the spiral casing decreases.6.The dynamic balance of a single blade impeller was studied by using dynamic balance testing machine and ADAMS virtual prototype respectively.It is found that the correction results of the two methods are the same in the front shroud,and the relative error of the correction results in the rear shroud is about 6%.The accuracy can meet the requirements by using the virtual prototype to correct the eccentric mass of the impeller.The radial force on the impeller before and after correction is analyzed.It is found that the radial force on the impeller after correction is reduced by about 54%. |
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