The unsteady behavior of a diffuser stall in a centrifugal compressor with a vaneless diffuser was investigated by experimental and computational analyses. The tested compressor is a design that was based on a turbocharger for marine diesel engines. The tested impeller is an open-shroud type with 7 main and splitter blades. The height of the diffuser was adopted for 19.55mm. In the experiments, the rotational speed is set to 6000 min^-1^ and the unsteady flow fields in the centrifugal compressor were investigated by pressure and velocity measurements. The pressure and velocity were measured from the diffuser inlet to diffuser exit. In the CFD analysis, Detached Eddy Simulation (DES) was used to establish numerical schemes to investigate the unsteady internal flow field. A full annulus analysis including the casing region was carried out to investigate the unsteady behavior of diffuser rotating stall.

From the pressure measurements, the diffuser stall was generated as the mass flow rate was decreased. The diffuser stall cell was rotated at 25-30 % of impeller rotational speed. The diffuser stall fluctuations could be observed at 180 deg from the cutoff. The magnitudes of diffuser stall fluctuations were gradually increased near the cutoff. From the velocity measurements at the diffuser inlet, the diffuser stall fluctuations were generated near both the shroud and hub side. Especially, the diffuser stall was appeared at 180 deg and 240 deg from the cutoff. From the CFD analysis, the unsteady behavior of the diffuser stall was simulated. The mass flow fluctuations at the diffuser exit showed the low mass flow region, which rotated at about 25% of impeller rotational speed. The low mass flow region was initiated at 180 deg from the cutoff and developed when this region reached the cutoff. Therefore, the diffuser stall could be simulated from the CFD analysis. First, the diffuser stall cell was initiated at 180 deg from the cutoff by the interaction with the boundary separation and the impeller discharge vortex. Then, the diffuser stall cell was developed by the accumulation of the boundary separation and induced the low velocity area, which was located at the center of the stall cell. The low velocity region formed the blockage at the all span of the diffuser passage. The velocity angle was remarkably increased ahead of the stall cell by the blockage formation. The diffuser stall cell was expanded to the impeller rotational direction because of the boundary separation caused by the positive flow angle. Finally, the diffuser stall cell was vanished when the stall cell passed by the cutoff, because the mass flow recovery was occurred.

Therefore, it was assumed that the diffuser stall behavior was initially occurred at 180 deg from the cutoff. Finally, the diffuser stall was expanded to the circumferential direction and developed to the blockage of the diffuser passages.


The Unsteady Behavior of Diffuser Stall in a Centrifugal Compressor With Vaneless Diffuser

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2020/volume/83709

18th International Conference on Nanochannels, Microchannels, and Minichannels
Paper Proceedings: https://asmedigitalcollection.asme.org/ICNMM/ICNMM2020/volume/83693

Fluids Engineering Division Summer Meeting
Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2020/volume/83716

HT-ICNMM2020 - Virtual Conference, SHTC - Virtual Conference, FEDSM2020 - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.