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Authors = Xavier Flete ORCID = 0009-0004-4891-5792

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20 pages, 7537 KiB  
Article
Analysis and Prediction of the Stability Limit for Centrifugal Compressors with Vaneless Diffusers
by Xavier Flete, Nicolas Binder, Yannick Bousquet, Viviane Ciais, Sandrine Cros and Nicolas Poujol
Int. J. Turbomach. Propuls. Power 2024, 9(3), 29; https://doi.org/10.3390/ijtpp9030029 - 5 Aug 2024
Viewed by 2568
Abstract
A numerical study was conducted to identify the mechanisms involved in the destabilisation of centrifugal compressors with vaneless diffusers. A stability analysis—carried out on the rotating and fixed parts of the studied machines—showed that the vaneless diffuser is a limiting component at a [...] Read more.
A numerical study was conducted to identify the mechanisms involved in the destabilisation of centrifugal compressors with vaneless diffusers. A stability analysis—carried out on the rotating and fixed parts of the studied machines—showed that the vaneless diffuser is a limiting component at a low mass flow rate. It was demonstrated that the reorganisation of stall patterns into recirculation in the inducer stabilises the impellers’ flow fields. As the destabilisation of vaneless diffusers has been a recurrent topic in the literature, many models have shown that it is the inlet-flow angle that drives the loss of stability. Models from the literature have estimated critical angle values using the geometry of the diffuser. Thus, for a given stage, expressing the diffuser inlet-flow angle as a function of the mass flow rate allows one to estimate its stability limit. However, this law needs to be calibrated to consider each compressor’s geometrical and aerodynamic specificities. This calibration can be achieved through single-passage steady simulations performed at stable operating points with high mass flow rates. With this methodology, a designer can estimate the stability limit of a centrifugal compressor with a vaneless diffuser from single-passage RANS calculations. Full article
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14 pages, 7623 KiB  
Article
Numerical Investigation of Rotating Instability Development in a Wide Tip Gap Centrifugal Compressor
by Xavier Flete, Nicolas Binder, Yannick Bousquet and Sandrine Cros
Int. J. Turbomach. Propuls. Power 2023, 8(3), 25; https://doi.org/10.3390/ijtpp8030025 - 1 Aug 2023
Cited by 3 | Viewed by 2138
Abstract
In the current study, full-stage unsteady simulations were performed to investigate rotating instability inception mechanisms in a particularly large tip clearance centrifugal compressor with a vaneless diffuser and a volute. Four operating points along a speed line were analysed to understand the influence [...] Read more.
In the current study, full-stage unsteady simulations were performed to investigate rotating instability inception mechanisms in a particularly large tip clearance centrifugal compressor with a vaneless diffuser and a volute. Four operating points along a speed line were analysed to understand the influence of the mass flow reduction on flow structures. Close to the peak efficiency, an unsteady interaction between the tip clearance vortices and splitter blades was observed. Considering other studies, the influence of the tip gap size was analysed. Then, a large-scale vortex shedding from the leading edges of the main blades was detected when the stage operated near the maximum pressure ratio. It was demonstrated that shed vortices were caused by the combination of the radial gradient of the tangential velocity under the tip vortex and the reverse backflow near the casing. Previous studies on axial compressors refer to these vortical structures as backflow vortices. These vortices cause a significant increase in the incidence angle in the tip region. Full article
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