Research On The Cavitation Performance And Instability Of Centrifugal Pump With Inducer

The inducer which is installed before the centrifugal pump can effectively improve the cavitation performance of the centrifugal pump. People put forward higher requirements on the stability and efficiency of the centrifugal pump with the development of the petroleum industry, chemical industry, electric power, etc. The cavitation performance not only determines the stability of the pump unit, but also has an effect on the efficiency of the pump. The essay takes a centrifugal pump with pre-positioned equal pitch inducer as the research object. Firstly, in order to determine the feasibility of the numerical calculation method used in the paper, the numerical calculation of single-phase steady flow was carried out and got the results, then compared with the experimental results. Secondly, based on the single-phase flow numerical results, the numerical calculation of cavitation steady flow was carried out under 0.6Q、1.0Q、1.2Q operating conditions, and the cavitation evolution, distribution of flow field of the centrifugal pump with inducer under different operating conditions were revealed,as well as the effect of the volute. Finally, to investigate the effect of wear-ring clearance on the cavitation performance of centrifugal pump with pre-positioned inducer, the cavitation flows and performances in the centrifugal pump with pre-positioned inducer were numerically simulated with four different projects which were 0.15mm、0.25mm、0.40 mm and 0.60 mm that the other components were kept unchanged and only the value of the wear-ring was changed under design condition. The main conclusions are as following:(1)The numerical calculation results of the original model(b2=0.25mm) under different operating conditions are close to the experimental results, and the numerical results are accurate and feasible.(2)With the decrease of the cavitation remainder, the cavitation performance curves of the inducer and the pump begin to drop when the cavitation number decrease to a certain extent. Both of the cavitation performance curves fluctuate most seriously under large flow, and small flow is less than large flow, the design flow is the least. The cavitation performance becomes poor when the pump runs in large flow rate.(3)Under the condition of small flow rate, the incipient cavitation and the fracture cavitation of the centrifugal pump with inducer appear at a certain point after the incipient cavitation and the fracture cavitation of the inducer, which can better improve the cavitation performance of the pump; Under the design condition, the incipient cavitation point is almost in the same in the inducer and the impeller, but the fracture cavitation of the impeller occurs after the inducer; Under large flow condition, cavitation occurs first in the impeller; which cannot meet the requirements of the energy of the centrifugal impeller, thus the pump is difficult to run in the large flow rate.(4)The rotor-stator interaction between the volute and the rotating impeller、 the existence of the inducer and the wear-ring make a contribution to the uneven distribution of the cavitation、alternating cavitation and unsteady cavitation.(5)The cavitation types in the centrifugal pump with inducer are: the vortex cavitation in the backflow regions and the blade cavitation,they are sheet cavitation which is relatively stable and the unsteady cloud cavitation. The distribution of cavitation in each channel is uneven in the impeller, so fracture cavitation occurs when part of the channel is blocked.(6)Cavitation changes the internal flow field in the impeller, with the decrease of cavitation remainder, the passages corresponding the cavitation areas produce vortex which are close to the outlet of the impeller suction surface and the direction is similar to the impeller, the smaller cavitation remainder, the more vortexes, and the vortex regions spread to the inlet of the impeller. With the increase of the flow rate, the effect of the rotor-stator interaction between the volute and impeller reduces, and the influence of cavitation on flow pattern is more than that of rotor-stator when the cavitation remainder is reduced to fracture condition.(7)The head loss in the volute starts increasing with the cavitation remainder decreasing to a certain extent, the flow pattern in the volute changes, and the changed location is corresponding to the serious cavitation region in the impeller passage.(8)The leakage flow of the wear-ring clearance has a greater influence on the head and the efficiency, with the increase of the wear-ring clearance, compared with b1,the total head、efficiency and the head、efficiency of the impeller are all decrease, the changes of the head are up to 0.6%、4.21%,as well as the efficiency are up to 6.5%、9.32%.but the head and the efficiency of the inducer are up to 29.86%、 28.40%. The influence of the efficiency is more significant with the increase of the wear-ring clearance.(9)The size of the wear-ring clearance has a greater influence on the cavitation performance, the cavitation curves wave as the increase of the wear-ring clearance and the decrease of the cavitation number and the wider the more obvious; the cloudy cavitation bubbles distribute on the pressure surface that is close to the front shroud, which causes cavitation instability and the wider the more unstable、the greater critical cavitation number.(10)It is found that the factors that influence the cavitation instability of pump are possibly related to the impact of high pressure leakage fluid of the wear-ring outlet on the main flow 、the occurrence of cavitation at the intersection of impeller inlet and wear-ring clearance outlet and the change of the outlet flow angel caused by cavitation in the pre-positioned inducer.