Abstract
A review on the rotating stall in the vaneless diffuser of centrifugal compressors is presented showing that different stall modes characterized by different numbers of cells can be detected within the diffuser even if the operating condition remains unchanged. The interaction between the inlet perturbation and the stall cells near the diffuser outlet is supposed to be the trigger of the stall mode transformation. In order to determine if the inlet perturbation will interact with the downstream stall cells, a characteristic time analysis is proposed to estimate the characteristic time of the perturbation in radial and tangential directions. An additional theoretical model which focused on the development of the vaneless diffuser rotating stall is presented to determine the propagation velocity of the cells. The comparison between the characteristic time in two directions shows that one stall mode is able to evolve into another stall mode if a critical condition is met, and the stall mode transformation is more likely to start from a mode with a higher number of cells and is more likely to occur in the diffuser with a large radius ratio. Experimental results are also employed to validate the proposed critical condition, and good agreements are obtained.
Highlights
Turbomachinery is undoubtedly important for modern industrialized society, especially in the fields of small and medium-sized aero-engines, refrigeration, chemical factory, vehicles, etc. [1,2,3,4,5].As power machinery, a wide, high-efficiency operating range is required for compressors, considering the efficiency and the stability and safety [6,7,8]
The critical condition indicated that the inlet perturbation can interact with the downstream stall cells if the flow angle is lower than a critical value associated with the diffuser radius ratio R, number of stall cells n, and the propagation velocity coefficient k; the number of stall cells could be changed, i.e. another stall mode can be expected if the critical condition is satisfied
A smaller radial velocity increases the time needed for the perturbation to flow out of the vaneless diffuser; the perturbation has sufficient time to interact with the stall cells in a circumferential direction; On the other hand, the interaction is more likely to happen when the inlet perturbation propagates with faster circumferential velocity
Summary
Turbomachinery is undoubtedly important for modern industrialized society, especially in the fields of small and medium-sized aero-engines, refrigeration, chemical factory, vehicles, etc. [1,2,3,4,5].As power machinery, a wide, high-efficiency operating range is required for compressors, considering the efficiency and the stability and safety [6,7,8]. The behaviors of compressor operating under off-design conditions are subject to various unstable phenomena which could have negative effects on their performance and lead to further increased losses and energy consumption. The volute, designed according to conservation of angular momentum, generates inhomogeneous static pressure distribution even under nominal conditions. It has been further analyzed how a pressure distortion propagates from a diffuser outlet to the impeller. Carretta et al [10] adopted a stability parameter (SP) to predict the stability limit; the contribution of each component to the compressor stability was analyzed, and the results showed that the vaned diffuser was responsible for the compressor instability. Bardelli et al [11] investigated the flow in the centrifugal stage of a compressor
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
