Theoretical Research On Stall Mode Of Wide Vaneless Diffuser In Centrifugal Compressor Based On Eigenvalue Solution

Centrifugal compressor was widely used in various fields of national economy because of its simple structure,wide stable running range and many other advantages.As an important part of centrifugal compressor,vaneless diffuser plays a key role in reducing gas velocity and increasing gas pressure.However,the problem of vaneless diffuser rotating stall has always restricted the safe operation of centrifugal compressor under the condition of small flow rate.It is of great significance to improve the reliability and design concept of the vaneless diffuser to study the phenomenon of rotating stall and realize active or passive control.In this paper,based on the core flow distortion theory,a two-dimensional stability model for the rotating stall of a wide vaneless diffuser was established and different stall modes in long and short vaneless diffuser were studied firstly.The two-dimensional flow equation inside the vaneless diffuser were linearized by small perturbation theory,and the equations were transformed into a generalized eigenvalue problem by canonical expansion.The stall model of the vaneless diffuser was established and solved by MATLAB.Secondly,a large number of experimental data in the literature were compared with the stall point data calculated by the model under the change of the number of stall cells and the radius ratio of vaneless diffuser.The results were in good agreement with the experimental data,and the calculation accuracy of the model for the relative speed of stall cells was verified.The different stall modes in the long and short vaneless diffusers were studied by using the model constructed in this paper.The results showed that the vaneless diffuser model constructed in this paper produced less stall cells during the rotating stall process,and the critical stall flow coefficient was lower,and the overall stable operation range was relatively wider;There were different stall modes in long and short vaneless diffusers,long vaneless diffuser stall pattern changes existed in the process of rotating stall,stall number was merged,and in the process of merging relative speed to reduce the phenomenon of stall regiment,and rotating stall in short vaneless diffuser did not exist in the process of stall pattern change phenomenon;when the radius ratio of vaneless diffuser and the installation angle of blade outlet were reduced,the critical stall flow coefficient and the relative speed of stall mass at the initial point of stall were reduced,which increased the stable operating range of centrifugal compressor.Finally,the discriminant criterion of distinguishing long and short vaneless diffusers was proposed according to the different stall modes of long and short vaneless diffusers found in this paper.By this criterion,the radius ratio of 1.64 was obtained as the threshold value to distinguish the theoretical model of long and short diffusers in this paper.