###### Abstract  
The influence of different diffuser configurations on the flow stability and aerodynamic performance of a centrifugal compressor stage with a mass flow coefficient of 0.196 is numerically investigated. Research results show that the performance of a traditional full-height vaned diffuser (TVD) deteriorates rapidly, and a shroud-side partial vaned diffuser (SVD) displays better adaptability in off-design conditions. SVD can suppress the development of vortices generating at the diffuser leading-edge. Therefore, it can reduce the flow loss inside the stage and improve the flow stability of the stage at low mass flow rates. The unsteady analysis for TVD and SVD shows that the stall cell propagates at about 35.7% of impeller rotational speed in the semi-vaneless space and diffuser passages. Furthermore, the internal flow in TVD and SVD is studied by employing the proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) methods. The flow loss and instability mechanism in the stage are consequently revealed more comprehensively. partial vaned diffuser; flow stability; compressor stage; unsteady analysis; proper orthogonal decomposition +
Footnote †: journal: Applied Sciences  
**Clinical. ** [PERSON]; [PERSON]; [PERSON]; [PERSON] Numerical Study of the Improvement in Stability and Performance by Use of a Partial Vaned Diffuser for a Centrifugal Compressor Stage. _Appl. Sci._**2021**, _11_, 6980. [[https://doi.org/10.3390/app11156980](https://doi.org/10.3390/app11156980)]([https://doi.org/10.3390/app11156980](https://doi.org/10.3390/app11156980))  
**Clinical. ** [PERSON]; [PERSON]; [PERSON]; [PERSON] Numerical Study of the Improvement in Stability and Performance by Use of a Partial Vaned Diffuser for a Centrifugal Compressor Stage. _Appl. Sci._**2021**, _11_, 6980. https://doi. [PERSON] et al. [3] changed the blade height of partial vaned diffusers and compared the aerodynamic performance. Research shows that there is an optimum vane height for each partial vaned diffuser. The application of a partial vaned diffuser can effectively suppress the corner separation flow, as demonstrated by [PERSON] et al. [4]. Based on experimental and simulation results, [PERSON] et al. [5] and [PERSON] et al. [6] pointed out that centrifugal compressors have higher stage performance when assembled with shroud-side partial vanes. In contrast, [PERSON] et al. [7] found that a hub-side vaned diffuser has higher pressure recovery and efficiency than a vaneless diffuser and has a wider operating range compared with a traditional vaned diffuser. [PERSON] et al. [8] showed that a hub-side vaned diffuser has a higher energy coefficient and a wider operating range under a certain vane height. The experimental and simulation investigations by [PERSON] et al. [9] indicated that the tapered vaned diffuser could reduce noise and enlarge the stable operating ranges by vortex control. Although numerous studies show that a partial vaned diffuser can efficiently improve the internal flow of the compressor, the conclusions about the arrangement of partial vanes as well as the details of the internal flow of the diffuser are somewhat contradictory. Moreover, the loss mechanism and dynamic characteristics of flow instability need further investigation. Therefore, this paper attempts to provide a comprehensive representation of the flow pattern of a centrifugal compressor assembled with different types of vaned diffusers to explore various flow losses and mechanisms of stability improvement. Firstly, detailed configurations of the diffuser and the numerical method are presented, and experimental data authenticate the accuracy of the numerical method. Then, according to unsteady time-averaged results, the performance and internal flow of different diffusers are investigated. Moreover, unsteady numerical simulations for TVD and SVD under low mass flow rate are carried out. The evolution process of the main vortex structures of the leading edge of diffuser vanes and the propagation law of the stall cell are described in detail.