Structure of Diffuser Stall and Unsteady Vortices in a Centrifugal Compressor With Vaned Diffuser

Fujisawa, Nobumichi; Ikezu, Sota; Ohta, Yutaka

doi:10.1115/gt2016-56154

Cited by 5 publications

(5 citation statements)

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“…As Bousquet et al accurately pointed out, the growth of the amplitude of a modal wave rotating in the vaneless space led to occurrence of the diffuser rotating stall; this was evident from the numerical analysis [11]. The authors also have reported that the unsteady behavior of the diffuser stall was influenced by the unsteady vortices at the leading edge of the diffuser vane during the off-design operation [12,13].…”

Section: Introductionmentioning

confidence: 70%

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Transition Process from Diffuser Stall to Stage Stall in a Centrifugal Compressor with a Vaned Diffuser

Fujisawa¹,

Ohta²

2017

International Journal of Rotating Machinery

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The transition process from a diffuser rotating stall to a stage stall in a centrifugal compressor with a vaned diffuser was investigated by experimental and numerical analyses. From the velocity measurements, it was found that the rotating stall existed on the shroud side of the diffuser passage in the off-design flow condition. The numerical results revealed the typical vortical structure of the diffuser stall. The diffuser stall cell was caused by the systematic vortical structure which consisted of the tornado-type vortex, the longitudinal vortex at the shroud/suction surface corner (i.e., leading edge vortex (LEV)), and the vortex in the throat area of the diffuser passages. Furthermore, the stage stall, which rotated within both the impeller and diffuser passages, occurred instead of the diffuser stall as the mass flow rate was decreased. According to the velocity measurements at the diffuser inlet, the diffuser stall which rotated on the shroud side was shifted to the hub side. Then, the diffuser stall moved into the impeller passages and formed the stage stall. Therefore, the stage stall was caused by the development of the diffuser stall, which transferred from the shroud side to the hub side in the vaneless space and expanded to the impeller passages.

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Section: Introductionmentioning

confidence: 70%

“…on conditions (a) and (b). Based on the previous report [12,13], this 55 Hz pressure fluctuation was caused by the impeller rotating stall.…”

Section: Transition To the Stage Stallmentioning

confidence: 99%

Transition Process from Diffuser Stall to Stage Stall in a Centrifugal Compressor with a Vaned Diffuser

Fujisawa¹,

Ohta²

2017

International Journal of Rotating Machinery

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“…One occurred at around 58 Hz and the other occurred at around 25-30 Hz. Based on previous report (Fujisawa et al, 2016), the unsteady phenomena at around 58 Hz were caused by a rotating stall within the impeller passages. On the other hand, the lower frequency fluctuation at around 25-30 Hz, was equivalent to 25-30% of the impeller rotating speed, and was caused by a rotating stall within the vaneless diffuser.…”

Section: Compressor Performance and Stall Characteristicsmentioning

confidence: 84%

Generation Mechanism of Diffuser Stall in a Centrifugal Compressor with Vaneless Diffuser

Fujisawa

Tajima

Miida

et al. 2020

J. Glob. Power Propuls. Soc.

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The generation mechanism of a diffuser stall in a centrifugal compressor with a vaneless diffuser was experimentally and computationally investigated, and the main findings are presented in this paper. Diffuser stall is generated when the mass flow through the compressor decreases and approaches the compressor surge limit. It was observed that diffuser stall cells rotate at 25-30% of the impeller rotational speed, with diffuser stall fluctuations observed at 180°from the cutoff (volute tongue). It was found that the magnitude of the diffuser stall fluctuation gradually increased near the cutoff. According to the CFD analysis, the mass flow fluctuations at the diffuser exit showed a low mass flow region, rotating at approximately 25% of the impeller rotational speed. The diffuser stall fluctuations began at 180°f rom the cutoff and developed as this region approached the cutoff. Therefore, the diffuser stall could be simulated by CFD analysis. First, the diffuser stall cell originated at 180°from the cutoff by the hub side boundary layer separation. Then, the diffuser stall cell further developed by the boundary layer separation accumulation and the induced low velocity area. The low velocity region formed a blockage across the diffuser passage span. The diffuser stall cell expanded due to the boundary layer separations occurring on the shroud and hub wall by turns. Finally, the diffuser stall cell vanished when it passed the cutoff, because the mass flow recovery occurred. The current paper presented the main results of this phenomena of great importance in centrifugal compressors.

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“…Vortex I is clockwise; it is affected by the tornado-like vortex and impacts the diffuser suction surface. Vortex B is counterclockwise; it rotates towards the pressure surface of the adjacent diffuser vane, blocks the mainstream in the diffuser passage, leads to increased flow loss, and even causes the diffuser to stall [23]. Comparing the vortex structures at the leading edges of TVD and SVD, it can be seen that the flow in the passage of the TVD diffuser is more complicated than that in SVD.…”

Section: Investigation Of the Flow Field In The Different Diffusersmentioning

confidence: 99%

Numerical Study of the Improvement in Stability and Performance by Use of a Partial Vaned Diffuser for a Centrifugal Compressor Stage

Liu

et al. 2021

Applied Sciences

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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.

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Structure of Diffuser Stall and Unsteady Vortices in a Centrifugal Compressor With Vaned Diffuser

Cited by 5 publications

References 0 publications

Transition Process from Diffuser Stall to Stage Stall in a Centrifugal Compressor with a Vaned Diffuser

Transition Process from Diffuser Stall to Stage Stall in a Centrifugal Compressor with a Vaned Diffuser

Generation Mechanism of Diffuser Stall in a Centrifugal Compressor with Vaneless Diffuser

Numerical Study of the Improvement in Stability and Performance by Use of a Partial Vaned Diffuser for a Centrifugal Compressor Stage

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