| In order to explore the mechanism of the influence of the casing profile of double acting liquid ring pump on its internal flow field and performance,a multi-stage double acting liquid ring compressor was taken as the research object to analyze the characteristics of the internal flow field at all stages.Based on the traditional elliptical structure,DFFD direct free-form surface deformation method is used to parametrically control the casing profile,and BBD experimental design method is used to build the response surface surrogate model of each performance parameter.Combined with NSGA-II multi-objective optimization method,the casing profile in the suction and exhaust areas is co-optimized.(1)Numerical analysis of complex gas-liquid flow in a multi-stage double acting liquid ring compressor was conducted,and the hydraulic performance of the pump and the characteristics of gas-liquid two-phase flow fields at all stages were studied.Research shows:The flow field inside the double acting liquid ring pump is basically radially symmetric,and the distribution pattern of the suction and exhaust areas and the flow field inside the impeller casing is basically consistent with that of the single acting liquid ring pump.The pressure of the multi-stage liquid ring compressor increases gradually,and the higher the stage,the smaller the gas phase area.Severe gas-liquid mixing and local over-compression occur in the second stage liquid ring compressor,with the most severe backflow occurring at both the beginning and end of the suction port.The third stage has the smallest back flow,and the flow patterns at the suction and exhaust ports are more stable.The shaft power of each stage of liquid ring compressor shows a trend of first increasing and then decreasing,and the flow rate,compression ratio,and efficiency gradually decrease.The compression ratio of the liquid ring compressor is7.895,and the pipeline and transition section transportation process loses 5.81%.When the liquid ring compressor operates under multiple operating conditions,as the outlet pressure increases,the suction volume gradually decreases,and the efficiency shows a trend of first increasing and then decreasing.The low-pressure area of the suction port gradually decreases,and the highest pressure is mainly distributed in the working liquid at the compression zone and radial clearance.(2)Explore the interactive response relationship between the casing profile disturbance of the double acting liquid ring compressor and various performance parameters,as well as the impact of a single disturbance on pump performance.Changes in pump performance under the interaction of various disturbances:the rate of flow mainly depends on the casing profile at the beginning and end of the inhalation port.When the R_A value approaches 0,the smaller the R_Bvalue,the better the effect of suction.The shaft power is mainly affected by the casing profile at the beginning of the suction and exhaust ports.The smaller the R_A and R_C values,the smaller the shaft power.The efficiency is mainly affected by the casing profile at the beginning and end of the suction port.The larger the R_A value,the smaller the R_B value,and the higher the efficiency.The impact of a single disturbance on performance:The casing profile at the beginning of the suction port has a significant impact on the suction volume.As the R_A value increases,the suction volume first increases and then decreases;The casing profile at the end of the suction port has a significant impact on efficiency,with R_B at a low level and efficiency tending to be the highest;The R_C value at the beginning of the exhaust port has no significant impact on the suction volume and efficiency;When the R_D value at the end of the exhaust port gradually increases,the suction volume and efficiency first decrease and then increase,but the fluctuation amplitude is small.The influence of case profile on gas-liquid interface:The greater the diffusion of the surface flow channel inside the suction area shell,the smaller the contraction rate of the exhaust area flow channel,and the greater the pressure difference between the working surface and the back of the blade.The more obvious the serrated shape of the gas-liquid interface in adjacent cavities,the greater the hydraulic loss caused,resulting in a significant increase in the shaft power of the double acting liquid ring compressor.(3)Based on the response surface surrogate model,the multi-objective optimization method was used to optimize the casing profile in the suction and exhaust areas,and the hydraulic excitation characteristics of gas-liquid flow in the pump were studied.Analysis shows that the optimal efficiency design scheme has increased traffic and efficiency by 1.4%and 1.53%respectively compared to the original model;The optimal traffic design scheme has increased traffic and efficiency by 16.4%and 0.61%respectively compared to the original model.The optimal efficiency scheme has poor transitional performance of the suction area casing profile,with a small increase in suction volume,but an increase in the contraction rate of the exhaust area flow channel,greatly improving the efficiency of the pump.In the scheme of maximum suction capacity,the diffusion degree of the flow passage in the suction area is reduced,and the transition of the casing profile at the beginning and end of the suction port is good.The suction capacity is significantly increased,while the contraction rate of the flow passage in the exhaust area is reduced,resulting in the deterioration of the stability of the gas-liquid interface in the impeller cavity along the directional stability of the shell width,and the reduction of efficiency.The radial force shows that the optimal efficiency scheme is smaller than the maximum suction capacity scheme,and the optimized schemes are all lower than the original model.The main frequency amplitude of pressure pulsation is positively correlated with the submergence depth of the impeller,and the optimal efficiency scheme has the most significant optimization effect on pressure pulsation inside the case. |
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