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Research Papers

Experimental and Numerical Investigation of the Unsteady Flow Field in a Vaned Diffuser of a High-Speed Centrifugal Compressor

[+] Author and Article Information
Klemens Vogel

LEC, Laboratory for Energy Conversion,
Department of Mechanical and
Process Engineering,
ETH Zurich,
Zurich 8092, Switzerland
e-mail: vogel@lec.mavt.ethz.ch

Reza S. Abhari

LEC, Laboratory for Energy Conversion,
Department of Mechanical and
Process Engineering,
ETH Zurich,
Zurich 8092, Switzerland

Armin Zemp

Laboratory for Acoustics/Noise Control,
Swiss Federal Laboratories for Materials Science and Technology,
Dübendorf 8600, Switzerland
e-mail: armin.zemp@empa.ch

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received September 29, 2014; final manuscript received October 27, 2014; published online December 30, 2014. Editor: Ronald S. Bunker.

J. Turbomach 137(7), 071008 (Jul 01, 2015) (9 pages) Paper No: TURBO-14-1259; doi: 10.1115/1.4029175 History: Received September 29, 2014; Revised October 27, 2014; Online December 30, 2014

Vaned diffusers in centrifugal compressor stages are used to achieve higher stage pressure ratios, higher stage efficiencies, and more compact designs. The interaction of the stationary diffuser with the impeller can lead to resonant vibration with potentially devastating effects. This paper presents unsteady diffuser vane surface pressure measurements using in-house developed, flush mounted, fast response piezoresistive pressure transducers. The unsteady pressures were recorded for nine operating conditions, covering a wide range of the compressor map. Experimental work was complemented by 3D unsteady computational fluid dynamics (CFD) simulations using ansys cfx V12.1 to detail the unsteady diffuser aerodynamics. Pressure fluctuations of up to 34.4% of the inlet pressure were found. High pressure variations are present all along the vane and are not restricted to the leading edge region. Frequency analysis of the measured vane surface pressures show that reduced impeller loading, and the corresponding reduction of tip leakage fluid changes the characteristics of the fluctuations from a main blade count to a total blade count. The unsteady pressure fluctuations in the diffuser originate from three distinct locations. The impact of the jet-wake flow leaving the impeller results in high variation close to the leading edge. It was observed that CFD results overpredicted the amplitude of the pressure fluctuation on average by 62%.

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References

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Figures

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Fig. 1

Centrifugal compressor test facility

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Fig. 2

Section of the impeller and instrumented diffuser

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Fig. 3

Pressure sensor positions in testrig and streamwise distribution on a vane

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Fig. 4

Experiment, FFT of pressure fluctuations—82.5% design RPM, SS, 18.6% streamwise location

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Fig. 5

Experiment, FFT of pressure fluctuations—78.2% to 85.0% of RPMDesign, pressure side, near stall, 47.6% streamwise location

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Fig. 6

Experiment, peak to peak pressure variation amplitudes, near stall

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Fig. 7

Experiment, peak to peak pressure variation amplitudes, design mass flow

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Fig. 8

Experiment, peak to peak pressure variation amplitudes, near choke

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Fig. 9

Experiment, pressure fluctuations on SS surfaces in a time-space diagram for two throttle settings, 82.5% design RPM: (a) near stall and (b) design

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Fig. 10

Experiment, pressure fluctuations on vanes PS surface in time-space diagram, near stall, 80.1% design RPM

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Fig. 11

CFD, pressure fluctuations on vanes suction side surface in a time-space diagram for two throttle settings, 82.5% design RPM: (a) near stall and (b) design

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Fig. 12

CFD, contour of static pressure in diffuser on midspan, design mass flow rate, 82.5% design RPM

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Fig. 13

CFD, pressure fluctuations on pressure side and suction side for 89.4% design RPM and design mass flow rate: (a) reflective OBC and (b) nonreflective OBC

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Fig. 14

Experiment, pressure fluctuations on pressure side and suction side for 89.4% design RPM and design mass flow rate

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Fig. 15

Maximum pressure variation amplitudes, experiment and CFD, 80.1% design RPM, near stall

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Fig. 16

Maximum pressure variation amplitudes, experiment and CFD, 89.4% design RPM, near stall

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