Study On Effect Of Slotted Blades On Low Specific Speed Centrifugal Pump Performance

High efficiency and small cavitation margin are always the major goals of a centrifugal pump by the researchers and engineers, and the performance of low specific speed centrifugal pump is low and difficult to improve due to the larger diameter of the impeller, smaller outlet width of the impeller and serious channel diffusion, even produce cavitation. Because the flow in impeller channel is usually complex and unstable, flow separation will appear in the downstream region of diffusion flow passage and it will result in unstable vortexes, which will block the flow passage and result in low pressure in centrifugal pump. Thus hydraulic efficiency is reduced; apart from that, separation will cause pump surge, which will cause severe vibration, noise and unstable operation. Therefore, in the hydraulic design flow separation should be avoided within the scope of design conditions.The influence of performance in centrifugal pump wit h Slotted blades was studied by numerical simulation and experimental design methods, using slotted blades flow control technology and M33-12.5 low specific speed centrifugal impeller.The main results of this study are as follows:1. Selection of parameters of slotted blades were studied and analyzed with CFD numerical simulation and experimental design methods. The results of orthogonal experiment show that the effect of parameters of slotted blades on the performance of low speed centrifugal pump is found in the primary and secondary order. Influence on the head as follows: diameter D of slotted > deflection angle β of slotted > width b of slotted > depth h of slotted > diffusion f of slotted; influence on the efficiency as follows: deflection angle β of slotted > diameter D of slotted > depth h of slotted > diffusion f of slotted > width b of slotted; influence on the cavitation margin as follows: depth h of slotted > diameter D of slotted > diffusion f of slotted > width b of slotted > deflection angle β of slotted. Comprehensive consideration, the effect of diameter of slotted、deflection angle of slotted and depth of slotted on the performance of centrifugal pump is great. According to the test results, the slotted model gets good results.2. Based on the analysis of the flow field, the re lative velocity, the blade load and jet- wake of original model with four kinds of slotted impeller to explore the mechanism of improving internal flow and cavitation performance with slotted blades, and studying the support and repression between the pressure flow velocity and cavitation in the flow channel, by the analysis of necking effect, jet flow, entrainment and the separation of the boundary layer. It was found that when the location of the slotted in the blade outlet, the head will have larger drop, however, when the deflection angle is negative, weakening of the impeller outlet jet- wake phenomena, improve the efficiency of the centrifugal pump; when the gap near the blade inlet, the performance of the centrifugal pump no improving effect, and even reduce the pump performance. It is easy to form a new turbulent vortex and the bubble region on the end of the back of slotted blade because of the pressure on the back side of the blade inlet has not yet been promoted, and the effect of the neck shrinkage effect and the entrainment effect.3. Through the numerical simulation of M33-12.5 and another constant- head pump find that, reasonable slotted blades could improve the performance of centrifugal pump. This verifies the slotted mechanism in the paper and provides a reference for the slotted design of low specific speed centrifugal pump. The selection range of slotted parameters: diameter of slotted D=0.5~0.7D2, deflection angle of slotted β= 45° ~ 70°, depth of slotted h=1.0, width of slotted b=1~3mm, diffusion of slotted f=1.2~1.5.