Study Of Inter-stage Matching Characteristics And Optimization For A Reversible Contra-rotating Axial Flow Pump

This paper focuses on the critical influence of inter-stage parameter matching on the performance of a reversible contra-rotating axial flow pump.The influence of axial spacing and speed ratio between two impellers of a reversible contra-rotating axial flow pump on the performance,flow characteristics,and pressure pulsation is studied with a numerical simulation method.The matching characteristics between contra-rotating stages in terms of axial spacing and speed are explained.Based on this,multi-factor optimization of the inter-stage matching parameters is carried out using the Isight platform to obtain the optimal values for the two-stage impeller axial spacing and speed matching,providing a theoretical basis for improving the performance of reversible contra-rotating axial flow pumps.The main research contents and conclusions are as follows:(1)Based on actual engineering conditions and required parameters,a numerical model of a reversible contra-rotating axial flow pump was designed,and numerical simulation calculations and analyses were conducted.The results show that the designed axial flow pump can meet the requirements of the high head,large flow rate,and bidirectional operation.However,there is a difference in impeller performance between the front and rear stages under design conditions.The efficiency of the front stage was 15%higher than that of the rear stage,and its shaft power was 34%lower.(2)The effects of axial spacing and speed ratio between contra-rotating stages on the hydraulic performance,flow characteristics,and pressure pulsation of the pump group were studied,and the matching characteristics of axial spacing and speed ratio between contra-rotating stages were explained.The results show that with an increase in the axial spacing coefficient δ,the efficiency curve of the reversible contra-rotating axial flow pump has multiple peaks.When the axial spacing coefficient δ was greater than 0.5,the performance of the pump changes periodically.The axial plane streamlines of the rear impeller,blade load,relative liquid flow angle,and outlet turbulence energy distribution also exhibited periodic changes with changes in axial spacing.When the axial spacing coefficient δ was 0.3,the amplitude of pressure pulsation between contra-rotating stages was large,and when δ was greater than 0.5,the amplitude of pressure pulsation remained basically unchanged as δ changes,and the mutual interference between contra-rotating stages was significantly reduced.(3)Within the studied speed range,as the speed ratio N increased,the total head of the pump linearly increased,and the total efficiency first increased and then decreased,with the pump group having a wide high-efficiency operating zone.With the increase of the speed ratio N,the outlet axial plane velocity of the front impeller steadily increased,and the turbulence energy and losses in the flow channel gradually increased;the inlet and outlet axial plane velocity distributions of the rear impeller fluctuated greatly,the flow state near the hub gradually deteriorates,and the turbulence energy gradually increased;the turbulent kinetic energy can be reduced near the edge of the wheel,the total hydraulic loss slowly decreases.The increase in the speed ratio causes the dominant frequency of pressure pulsation at each monitoring point between contra-rotating stages to gradually shift backward,and the amplitude also increases.(4)Based on the Isight optimization platform,a multi-island genetic algorithm was used to optimize the inter-stage matching parameters of the reversible contra-rotating axial flow pump,and the optimal axial spacing coefficient δ is 0.52,the speed ratio N is 1.18,and the corresponding efficiency of the pump were improved by 2.3%,with the maximum shaft power of a single stage impeller decreasing by 8.4%.After optimization,the distribution of the inlet axial plane velocity of the rear impeller was more uniform,the vortex near the pressure surface disappeared,the turbulence energy on the pressure surface and in the flow channel was significantly weakened,and the distribution range of high entropy production region is significantly reduced,with the losses of the rear impeller and outlet section reduced considerably.After optimization,pressure pulsation amplitude at each monitoring point between contra-rotating stages slightly increases,and the dominant frequency shifts forward.