Analysis And Optimization Of Diffuser/Volute Combinations For The Last Stages Of Centrifugal Compressors

Centrifugal compressors play an important role in many fields for their special advantages such as high reliability,low volume and weight.At the same time,extensive application also means that they will consume a large amount of energy sources.In many industry fields,as the increasingly strict requirements of high load,high efficiency and some other special demands,more researches on centrifugal compressors are imperative.Because of the complex structure,previous works on centrifugal compressors mainly focused on one single part.With the development of computer technology,more and more researchers begin to pay attention to the matching of each part in order to improve the whole stage performance of the centrifugal compressor.This thesis focused on the last stages of two typical centrifugal compressors.A numerical analytic system was developed based on the commercial software Pro/Engineer and NUMECA.Several geometry models on propylene compressor with different D₄/D₂ were built and experimented numerically.Flow inside the last stage of centrifugal compressor was analyzed and the best value of D₄/D₂ was concluded.Different type volutes were combined with the same diffuser and impeller so as to find the influence between the upstream and downstream parts.According to the law of conservation of momentum torque,the internal volute with constant breadth was designed and the modification was proposed by reducing the length of vaneless diffuser.As a consequence,the efficiency of the last stage was successfully increased by 1.8%.The influence of the diffuser length on stage performance with big flow coefficient was less than the stage with small and middle flow coefficient,based on the simulation on the pyrolysis compressor.Other factors such as the volute orientation,the chamfer of the clapboard also have influence on the stage performance.The research results presented in this thesis may provide some guidelines for flow analysis and structure modifications of the volute and diffuser and the optimization of the whole stage.