Abstract
The operating range of axial flow pumps is often constrained by the onset of rotating stall. An improved method using a double inlet nozzle to stabilize the performance curve is presented in the current study; a single inlet nozzle and three kinds of double inlet nozzle with different rib gap widths at the inlet of axial flow pump impeller were designed. Three dimensional (3D) incompressible flow fields were simulated, and the distributions of turbulence kinetic energy and velocity at different flow rates located at the inlet section, as well as the pressure and streamline in the impeller, were obtained at the same time. The single inlet nozzle scheme and a double inlet nozzle scheme were studied; the experimental and numerical performance results show that although the cross section is partly blocked in the double inlet nozzle, the head and efficiency do not decline at stable operation flow rate. On small flow rate condition, the double inlet nozzle scheme effectively stabilized the head-flow performance, whereby the block induced by the backflow before the impeller was markedly improved by using a double inlet nozzle. It has also been found that the rib gap width impacts the efficiency curve of the axial flow pump.
Highlights
The characteristic of the axial flow pump is that it has a good hydraulic performance near the design flow rate; if the flow rate deviates, the hydraulic performance of the axial flow pump will decrease [1]
The axial flow pump will produce violent vibrations and noise when it runs in saddle zone, and at the same time, the hydraulic loss of the axial flow pump will increase, which will reduce the effective head of the pump and seriously affect the stability of the pump
Considering the saddle-shape performance curve is caused by impeller blade inlet backflow, in order to stabilize the axial flow pump in the saddle area, reduce the flow channel blockage caused by backflow, and study the influence of the gap size of different inlet nozzles on the flow characteristics inside the axial flow pump, a new type of double inlet nozzle scheme is proposed in this paper
Summary
The characteristic of the axial flow pump is that it has a good hydraulic performance near the design flow rate; if the flow rate deviates, the hydraulic performance of the axial flow pump will decrease [1]. It is considered that saddle-shape appearance of an axial-flow pump performance curve is due to the rotating stall in impeller channels, as well as the alternation of low-pressure and high-pressure in impeller channels and corresponding jet-flow and backflow [2,3,4]. Considering the saddle-shape performance curve is caused by impeller blade inlet backflow, in order to stabilize the axial flow pump in the saddle area, reduce the flow channel blockage caused by backflow, and study the influence of the gap size of different inlet nozzles on the flow characteristics inside the axial flow pump, a new type of double inlet nozzle scheme is proposed in this paper. The research results can provide some reference to improve the operation stability of the axial flow pump under the condition of small flow rate
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