Effect of Unsteadiness on the Performance of a Transonic Centrifugal Compressor Stage

́binjac, Isabelle Tre; Kulisa, Pascale; Bulot, Nicolas; Rochuon, Nicolas

doi:10.1115/gt2008-50260

Cited by 13 publications

(21 citation statements)

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“…As already observed in a previous work [10], a better correspondence is obtained between experiment and unsteady simulations compared to the stationary ones. In particular, the steady-state computations overvalue the blockage massflow and the pressure ratio of the compressor stage.…”

Section: Overall Performancesupporting

confidence: 87%

“…This code solves the compressible RANS equations by a cell-centered finite volume method. The turbulence model chosen for this study is the two-equation model of Smith (k-l), that was shown by Rochuon [9] and Trébinjac et al [10] to provide results in a good accordance with the experiments in the case of a transonic centrifugal compressor stage. Both steady-state and unsteady numerical computations were performed.…”

Section: Numerical Proceduresmentioning

confidence: 99%

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Study and Control of a Radial Vaned Diffuser Stall

Marsan

Trébinjac

Coste

et al. 2012

International Journal of Rotating Machinery

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The aim of the present study is to evaluate the efficiency of a boundary layer suction technique in case of a centrifugal compressor stage in order to extend its stable operating range. First, an analysis of the flow pattern within the radial vaned diffuser is presented. It highlights the stall of the diffuser vanes when reaching a low massflow. A boundary layer separation in the hub-suction side corner grows when decreasing the massflow from the nominal operating point to the surge and finally leads to a massive stall. An aspiration strategy is investigated in order to control the stall. The suction slot is put in the vicinity of the saddle that originates the main separating skin-friction line, identified thanks to the analysis of the skin-friction pattern. Several aspiration massflow rates are tested, and two different modelings of the aspiration are evaluated. Finally, an efficient control is reached with a removal of only 0,1% of the global massflow and leads-from a steady-state calculations point of view-to an increase by 40% of the compressor operating range extent.

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Section: Overall Performancesupporting

confidence: 87%

Section: Numerical Proceduresmentioning

confidence: 99%

Study and Control of a Radial Vaned Diffuser Stall

Marsan

Trébinjac

Coste

et al. 2012

International Journal of Rotating Machinery

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“…In this machine, the surge is thought to initiate in the diffuser passages. Indeed it has been shown [3] that the diffuser was the most sensitive component to unsteadiness which came from two sources: the jet-wake structure (emanating from the impeller flow) and the interaction between the diffuser vane bow shock wave and the impeller blade pressure surface leading to pressure waves which propagate in the diffuser passages.…”

Section: Test Rigmentioning

confidence: 99%

“…The global shape and the amplitude of the fluctuations are consistent and help to show the reliability of the results. Refer to [3] for more information about the URANS calculation. Fig.…”

Section: Processing Of the Raw Datamentioning

confidence: 99%

Unsteady pressure measurements in a high-speed centrifugal compressor

2010

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This paper presents the unsteady data acquisition system used to measure the pressure field in high speed compressors. Details and electronic sketches are given for the conditioners developed in-house that have been used to amplify and to filter the pressure signal with the aim of acquiring data up to 150 kHz. A discussion of the experimental results carried out in a centrifugal compressor is proposed. Through different processing of the pressure signals and a comparison with URANS simulations, the excitation of the pressure transducers by the pressure waves generated by shock waves that occur between the impeller and the diffuser is highlighted. The levels of pressure fluctuations measured when entering into surge are also presented and reveal very repetitive behaviour of the flow instabilities.

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“…[7][8][9][10]. It is generally agreed that the effects of this unsteady flow on diffuser performance are limited at design conditions.…”

Section: Introductionmentioning

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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Effect of Unsteadiness on the Performance of a Transonic Centrifugal Compressor Stage

Cited by 13 publications

References 0 publications

Study and Control of a Radial Vaned Diffuser Stall

Study and Control of a Radial Vaned Diffuser Stall

Unsteady pressure measurements in a high-speed centrifugal compressor

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

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