Mechanistic Study Of The Effect Of Gap Drainage Impellers On The Performance Of Low Specific Speed Centrifugal Pumps

The improvement of pump efficiency and stability has been the focus and goal of centrifugal pump research,low specific speed centrifugal pump due to the narrow and long flow path,which aggravates the disc friction loss and liquid diffusion in the flow path,resulting in low performance,while compared with medium and high specific speed centrifugal pump is more prone to flow separation and turbulence phenomena,easy to trigger a series of vibration noise and other phenomena affecting the stable operation of the centrifugal pump,so improve its non-steady state characteristics,improve the stability of low specific speed centrifugal pump operation is also one of the research hot spots and difficulties of low specific speed centrifugal pump.In recent years,some scholars have discovered a gap drainage impeller that exhibits good characteristics in the pneumatic field and have tried to apply it in the field of centrifugal pumps.In this paper,based on the ZA20-250 low specific speed centrifugal pump,the effect of the gap drainage impeller on the performance of the low specific speed centrifugal pump is investigated,the orthogonal design and numerical calculations combined with experiments.The full text of the work is as follows:(1)A brief review of the current state of researches on gap drainage impellers in the field of pneumatics and pumps,and an exploration of the application of CFD technology in low specific speed centrifugal pumps.(2)Numerical calculation analysis,pump performance test and pressure pulsation test were carried out on ZA20-250 low specific speed centrifugal pump,and the results of numerical calculation and test results were compared,which showed that the numerical calculation results and test results had a high degree of agreement,verified the accuracy of the numerical calculation method,and laid a foundation for subsequent analysis and research.(3)In this paper,an orthogonal test was used to design a gap drainage impeller,and the orthogonal factors of slit diameter,gap width,and blade overlap length were selected.According to orthogonal test results found that at the different flow the impact of the gap drainage impeller is different.When 0.6Q_d the impact of the head and efficiency of the primary order is slit diameter?gap width?blade overlap length,when 1.0Q_d and 1.4Q_d the impact of the head of the primary order is gap width?slit diameter?blade overlap length,when 1.0Q_d the impact of efficiency of the primary order is gap width?slit diameter?blade overlap length,when 1.4Q_d the impact of efficiency of the primary order is slit diameter?gap width?blade overlap length.Therefore,the slit diameter and the gap width are the main parameters that affect the performance of the gap drainage impeller.(4)In order to further investigate the mechanism of the influence of the slit diameter and the gap width on the gap drainage impeller,four gap drainage impeller models were designed,with slits at 90mm and 180mm diameter,and slit widths of 1.5mm and 6.0mm at the same slit location,respectively.The results show that a reasonably open slit to drain the impeller can inhibit the flow separation at the pressure surface of the blade,improve the flow of liquid within the impeller,and reduce liquid blockage in the flow path.When using the same gap width,different slit diameters on the performance of the gap drainage impeller has a big difference,the performance of the slit in the front of the vane is better than the slit in the trailing edge of the vane,when using the same slit diameter,the smaller gap width can get better pump performance,the too much gap width will cause a sharp decline in pump performance.(5)Non-stationary calculations were performed on five models,and the differences in non-stationary pressure pulsations and radial forces between gap drainage impellers and conventional impellers were compared and analyzed to further understand the differences in slit diameter and gap width in the non-stationary characteristics of centrifugal pumps.The results show that reasonable slitting can reduce the pressure pulsation and radial force and improve the operational stability of the pump.Slitting in the front of the vane reduces the pressure pulsation in the centrifugal pump when the small flow condition,the influence of pressure pulsation in the centrifugal pump when the large flow is weaker,while the radial force decreases.Slitting in the trailing edge of the vane weakens the pressure pulsation spread in the centrifugal pump,the pressure pulsation downstream of the volute channel appears sharp decay,but the radial force increases while the frequency of alternating action increases,destroying operational stability.