An Investigation of Stall Inception in Centrifugal Compressor Vaned Diffusers

Everitt, Jonathan; Spakovszky, Z. S.

doi:10.1115/gt2011-46332

Cited by 15 publications

(12 citation statements)

References 30 publications

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“…For example, Everitt et al [10] reported the similar unsteady vortices at the diffuser leading edge in a high speed centrifugal compressor, as with the case of our paper. Furthermore, we confirmed that the LEV had the same form at high speed and the size of the LEV was increased at low mass flow late by CFD analysis, as we have mentioned in our previous paper [12].…”

Section: Structure Of Diffuser Stallsupporting

confidence: 72%

“…For example, Spakovszky reported that four-cell backward travelling modal waves occur in the vaneless space prior to the surge [9]. Everitt et al reported the generation mechanism of spike stall inception by numerical analysis [10]. The short wavelength stall inception in centrifugal compressors with vaned diffusers was caused by the separation on the shroud side of the diffuser leading edge and radial flow reversal throughout the vaneless space.…”

Section: Introductionmentioning

confidence: 99%

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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: Structure Of Diffuser Stallsupporting

confidence: 72%

Section: Introductionmentioning

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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“…The CFD setup of this work follows guidelines presented by Everitt [15]. Structural hexahedra, multi-block grids are automatically generated in the "AutoGrid" environment.…”

Section: General Description Of Cfd Calculationsmentioning

confidence: 99%

Area-Schedule Based Design of High Pressure Recovery Radial Diffusion Systems

Gao

Spakovszky

Rusch

et al. 2016

Volume 2D: Turbomachinery

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To address the shortcomings of the commonly used channel diffuser and cascade design perspectives, a streamtube perspective is adopted by carefully scheduling the streamtube area with special attention to the diffuser entry region. A design framework for radial diffusion systems is developed based on area scheduling the vaned diffuser. The vaned diffuser and volute designs are assessed numerically through RANS calculations and validated by full-scale compressor experiments. The investigations revel that it is mainly the diffuser area ratio and effective non-dimensional diffusion length that set diffuser performance. A careful balance between these two parameters is shown to enable high diffuser pressure recovery.The diffusion in the semi-vaneless-space, controlled chiefly by the vane suction side geometry, plays a key role in improving diffuser performance. Removing excess thickness from the suction side eliminates flow overspeed, increases effective diffusion length, and leads to higher pressure recovery at reduced stagnation pressure loss. The pressure side thickness distribution controls the channel area schedule. Thin leading edges ensure smooth flow area transition into the channel, and reduce the vane upstream influence and therefore pressure fluctuations as perceived by the impeller.A diffuser design based on the area schedule approach is tested experimentally. A 1.8 fold improvement in diffuser performance parameter CP/C,,, where C, and CPt are the diffuser static pressure recovery and the diffuser stagnation pressure loss coefficients respectively, is achieved. In addition, a 0.8% point increase in impeller isentropic efficiency due to reduced vane upstream influence and a 0.74% point increase in impeller-diffuser efficiency are demonstrated. The impact of the volute on diffuser and overall diffusion system performance is also assessed. High diffuser exit Mach numbers and a low volute inlet swirl parameter are shown to reduce volute performance.

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“…The Spalart-Allmaras turbulence model is used following successful application in past work [19]. According to best practice, y+ ranges from 1-10 for the first cell off the wall.…”

Section: Computational Approachmentioning

confidence: 99%

The Role of Impeller Outflow Conditions on the Performance of Vaned Diffusers

Everitt

Spakovszky

Rusch

et al. 2017

Journal of Turbomachinery

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Highly-loaded impellers, typically used in turbocharger and gas turbine applications, exhaust an unsteady, transonic flow that is non-uniform across the span and pitch and swirling at angles approaching tangential. With the exception of the flow angle, conflicting data exist regarding whether these attributes have substantial influence on the performance of the downstream diffuser. This paper quantifies the relative importance of the flow angle, Mach number, non-uniformity and unsteadiness on diffuser performance, through diffuser experiments in a compressor stage and in a rotating swirling flow test rig. This is combined with steady and unsteady Reynolds-Averaged Navier Stokes computations. The test article is a pressure ratio 5 turbocharger compressor with an airfoil vaned diffuser. The swirling flow rig is able to generate rotor outflow conditions representative of the compressor except for the periodic pitchwise unsteadiness, and fits a 0.86 scale diffuser and volute. In both rigs, the time-mean impeller outflow is mapped across a diffuser pitch using miniaturized traversing probes developed for the purpose.Across approximately two-thirds of the stage operating range, diffuser performance is well correlated to the average impeller outflow angle when the metric used is effectiveness, which describes the pressure recovery obtained relative to the maximum possible given the average inflow angle, Mach number and the vane exit metal angle. Utilizing effectiveness captures density changes through the diffuser at higher Mach numbers; a 10% increase in pressure recovery is observed as the inlet Mach number is increased from 0.5 to 1. Further, effectiveness is shown to be largely independent of the timeaveraged spanwise and unsteady pitchwise non-uniformity from the rotor; this independence is reflective of the strong mixing processes that occur in the diffuser inlet region. The observed exception is for operating points with high timeaveraged vane incidence. Here, it is hypothesized that temporary excursions into high-loss flow regimes cause a nonlinear increase in loss as large unsteady angle variations pass by from the rotor.Given that straight-channel diffuser design charts typically used in preliminary radial vaned diffuser design capture neither streamtube area changes from impeller exit to the diffuser throat nor vane incidence effects, their utility is limited. An alternative approach, utilizing effectiveness and vane leading edge incidence, is proposed. INTRODUCTIONModern high pressure ratio centrifugal compressors typically utilize a high speed impeller with backswept blades and a vaned diffuser. As part of ongoing efforts for a systemwide reduction in weight, increase in efficiency and/or reduction of emissions, designers seek to improve the pressure ratio, operating range and efficiency of the centrifugal compressor, which is often limited by the diffuser. Despite the relative simplicity of its geometry, the flow in the diffuser is complex and there is no well-established, reliable approach to gui...

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An Investigation of Stall Inception in Centrifugal Compressor Vaned Diffusers

Cited by 15 publications

References 30 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

Area-Schedule Based Design of High Pressure Recovery Radial Diffusion Systems

The Role of Impeller Outflow Conditions on the Performance of Vaned Diffusers

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