Research Papers

Vaned Diffuser Induced Impeller Blade Vibrations in a High-Speed Centrifugal Compressor

[+] Author and Article Information
Armin Zemp

e-mail: zemp@lec.mavt.ethz.ch

Reza S. Abhari

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

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Turbomachinery. Manuscript received June 18, 2012; final manuscript received August 15, 2012; published online November 2, 2012. Editor: David Wisler.

J. Turbomach 135(2), 021015 (Nov 02, 2012) (9 pages) Paper No: TURBO-12-1071; doi: 10.1115/1.4007515 History: Received June 18, 2012; Revised August 15, 2012

Blade failure in turbomachinery is frequently caused by an excessive resonant response. Forced response of the blades typically originates from unsteady fluid structure interactions. This paper presents the experimental and computational results of a research effort focusing on the blade forced response in a high-speed centrifugal compressor caused by the downstream vaned diffuser. The potential field from the downstream vaned diffuser acts as an unsteady impeller relative circumferentially nonuniform disturbance. In this work the effect of varying the radial gap between impeller exit and diffuser vane leading edges was examined. Dynamic strain gauges, which were installed on the blade surfaces, were used to measure the forced response levels of the blades and to estimate the damping properties for different compressor operating conditions and vaneless gap dimensions. Unsteady fluid flow simulations were used to quantify the forcing function acting on the compressor blades due to impeller-diffuser interaction. The time-resolved blade pressure distribution showed the temporal evolution of the dynamic load on the blade surface caused by the diffuser's potential field. The magnitude of the vibratory stress levels was found to depend on the radial gap size, the blade damping properties, and on the compressor operating point. The variation of the radial gap size resulted in a shift of the impeller-diffuser interaction zone towards the main blade leading edge by up to 5% of the streamwise location.

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Fig. 1

Centrifugal compressor test facility

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Fig. 2

Impeller equipped with dynamic strain gauges

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Fig. 3

Diffuser vane shape

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Fig. 4

Measured compressor performance for both diffuser geometries

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Fig. 6

Interferometric visualization of main bade mode shapes 6–8, view on suction side surface, leading edge on the right

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Fig. 7

Measured Campbell diagram

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Fig. 8

Measured vibratory blade stress amplitude, large radial gap, blade modes 6 to 8

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Fig. 9

Measured vibratory blade stress amplitude, small radial gap, blade modes 6 to 8

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Fig. 10

Effect of operating point on critical damping ratio ζ, small radial gap, blade mode 6

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Fig. 11

Critical damping ratio ζ, blade modes 6–8, design throttle setting, small radial gap

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Fig. 12

Critical damping ratio ζ/ζmat, blade modes 6–8, near-stall operating line, small radial gap

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Fig. 13

Critical damping ratio ζ, blade mode 6

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Fig. 14

Measured and computed total pressure ratios

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Fig. 15

Contour plot of streamwise velocity and vector plot of velocity at 50% span

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Fig. 16

Computed blade pressure fluctuation Δp′ at midspan, mode 8, small radial gap, near-stall throttle setting

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Fig. 17

Computed unsteady blade pressure amplitude Δp′, near-stall throttle setting




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