Study On Mechanisms And Characteristics Of Rotating Stall In Vaneless Diffuser

As one of the typical turbo machines, centrifugal compressor is widely used in various fields of national economy. However, its crucial components, diffuser suffers from a kind of unstable flow phenomena called rotating stall under small flow rate. Research on rotating stall will be of great significance in enhancing the operation range and reliability of centrifugal compressor.Supported by military accompanying project-study on diffuser stall mechanism and prevention technology, study was carried out on rotating stall in vaneless diffuser. Wide and narrow diffusers trapped into stall for boundary layer separation and two-dimensional mixed region instability respectively, the results were proved by theory analysis and numerical simulation. The main work of this thesis can be described as followings:First, based on abundant literature and simulation results, it was proposed that different stall mechanisms exist for wide and narrow diffusers and the derivation of the two stall models was given in detail.Secondly, numerical simulations were carried out by coupling the impeller and diffuser. After verifying the validity by comparing to the experimental data in literature, study was focused on the effect of diffuser width on stall. Performance curve and flow field analysis demonstrated wide and narrow diffusers had completely different stall characteristics.Then based on two-dimensional mixed region instability, two-dimensional model was adopted after simplification to study the influences of diffuser radius ratio and jet-wake structure parameters on stall characteristics. Under the ideal conditions of uniform inlet, correlations were given to predict the critical flow coefficient and stall region number, predicted results agreed well with the simulations.Finally aimed at convergent diffuser, the influence of converging shape, location, degree and length was analyses to obtain key parameters and relatively gpod scheme.In this paper, stall in vaneless diffuser was preliminarily studied through theory analysis and numerical simulation, the results would deepen the understanding of stall mechanism and characteristics, and it was expected to provide a reference for further experiment design and optimization schemes.