Effects of Inlet Flow Field Conditions on the Performance of Centrifugal Compressor Diffusers: Part 2 — Straight-Channel Diffuser

Deniz, Sabri; Greitzer, E. M.; Cumpsty, N. A.

doi:10.1115/98-gt-474

Cited by 8 publications

(15 citation statements)

References 2 publications

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“…Hence, we can expect the diffuser static pressure recovery to be affected by the flow non-uniformity at impeller exit. Filipenco et al [2000] and Deniz et al [2000] showed that mass-averaged stagnation pressure at diffuser inlet is satisfactory in correlating the diffuser pressure recovery. Based on the above considerations, it is appropriate to express the results on a mass average basis.…”

Section: Conceptual Choices For Averaged Resultsmentioning

confidence: 99%

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Aerospace Turbomachinery Flow Physics

Tan¹

2003

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Public reporting burden for this collection of information is estimated to average 1 hour per response, inclt turces, gathering and maintaining the data needed, and completing and reviewing the collection of information. S of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Ser% fferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Pa

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Section: Conceptual Choices For Averaged Resultsmentioning

confidence: 99%

“…Philips [1997], Filipenco et al [2000] and Deniz et al [2000] showed that vaned diffuser channel performance is weakly dependent on inlet blockage, but strongly affected by momentum-averaged flow angle. The three authors used the following definition for the momentum-averaged flow angle:…”

Section: Conceptual Choices For Averaged Resultsmentioning

confidence: 99%

Aerospace Turbomachinery Flow Physics

Tan¹

2003

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“…The pump model consists of an inlet casing(1), the 7 blades impeller(2), the vaned diffuser(3), having 12 vanes and an annular ring guiding the flow to the discharge pipe (4). The relative gap between the impeller trailing edge and the diffuser leading edge was 5.8%.…”

Section: Experimental Setup Test Pump and Test Loopmentioning

confidence: 99%

“…These flow separations affect negatively the operational behavior of these machines causing reduced efficiency, higher pressure pulsations and increased vibration levels. A variety of numerical and experimental studies on flow separation and unsteady phenomena in centrifugal compressors have been published (Frigne and Van Den Braembussche [1], Haupt et al [2] Filipenco et al [3], Deniz et al [4]), while the number of research publications regarding centrifugal pumps is relatively limited. Hergt and Benner [5] analyzed different diffusers in a free surface test stand at very low rotational speeds.…”

Section: Introductionmentioning

confidence: 99%

Experimental Investigation of Flow Instabilities and Rotating Stall in a High-Energy Centrifugal Pump Stage

Berten

Dupont

Fabre

et al. 2009

Volume 1: Symposia, Parts A, B and C

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In centrifugal pumps, the interaction between the rotating impeller and the stationary diffuser generates specific pressure fluctuation patterns. When the pump is operated at off design conditions, these pressure fluctuations increase. The resulting rise of mechanical vibration levels may negatively affect the operational performance and the life span of mechanical components. This paper presents detailed pressure fluctuation measurements performed in a high speed centrifugal pump stage at full scale at various operating conditions. The impeller and stationary part (diffuser, exit chamber) of the pump stage have been equipped with piezo-resistive miniature pressure sensors. The measured data in the impeller have been acquired using a newly developed onboard data acquisition system, designed for rotational speeds up to 6000 rpm. The measurements have been performed synchronously in the rotating and stationary domains. The analysis of pressure fluctuations at the impeller blade trailing edge, which had significantly larger amplitudes as the pressure fluctuations in the stationary domain, allowed the detection and exploration of stalled channels in the vaned diffuser. This stall may be stationary or rotating with different rotational speeds and number of stalled channels, depending on the relative flow rate and the rotational speed of the pump. The stall yields pressure fluctuations at frequencies which are multiples of the rotational speed of the impeller and generates additional sources of mechanical excitation. [6] performed pressure fluctuation measurements in the impeller and different diffusers at varying radial gaps between the impeller and the diffuser. He observed sidebands in the impeller pressure fluctuation spectra generated by a modulation between the vane passing frequency and the rotation frequency due to an uneven circumferential pressure distribution. Guo and Maruta [7] performed pressure fluctuation measurements in a centrifugal pump impeller and they found at high flow rates sidebands in the pressure fluctuation spectra. These sidebands were also a result of a modulation of the vane passing frequency with an uneven circumferential pressure distribution. Eisele et al. [8] used LDV and PTV techniques for a detailed flow analysis in a centrifugal pump diffuser at different operating points of the pump. At part-load flow rate they observed recirculation from the diffuser back into the impeller. Sano et al. [9] used CFD for the numerical simulation of the flow in a diffuser connected to an impeller using a moving grid method. The calculations were made "quasi" 2D, the mesh in the ground view was only one element high. Resulting from the simulation, diffuser rotating stall rotating with 10% of the rotational speed has been found. The simulated flow pattern was in accordance with the measurements of Hergt and Benner [5], Sinha et al. [10] and Wang and Tsukamoto [11]. While in the case studied by Sinha the gap between diffuser and impeller vanes was relatively large (20% of impeller radius), in ...

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“…In a two-part paper, Filipenco and Deniz et al [3,4] argue that radial vaned diffuser pressure recovery performance correlate uniquely to the momentum averaged inflow angle, as long as the pressure recovery coefficient is defined using the "availability average" inflow total pressure. This method of averaging best captures the relevant flow quantities for the diffuser, and under most flow conditions is very similar to the mass flow average [5].…”

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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Effects of Inlet Flow Field Conditions on the Performance of Centrifugal Compressor Diffusers: Part 2 — Straight-Channel Diffuser

Cited by 8 publications

References 2 publications

Aerospace Turbomachinery Flow Physics

Aerospace Turbomachinery Flow Physics

Experimental Investigation of Flow Instabilities and Rotating Stall in a High-Energy Centrifugal Pump Stage

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

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