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Research Papers

Numerical and Experimental Fluid–Structure Interaction-Study to Determine Mechanical Stresses Induced by Rotating Stall in Unshrouded Centrifugal Compressor Impellers

[+] Author and Article Information
B. Mischo

MAN Diesel & Turbo Schweiz AG,
Hardstrasse 319,
Zürich 8005, Switzerland
e-mail: bob.mischo@man.eu

P. Jenny, S. Mauri, Y. Bidaut, M. Kramer

MAN Diesel & Turbo Schweiz AG,
Hardstrasse 319,
Zürich 8005, Switzerland

S. Spengler

MAN Diesel & Turbo SE,
Stadtbachstr. 1,
Augsburg 86153, Germany

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 12, 2018; final manuscript received September 5, 2018; published online October 10, 2018. Editor: Kenneth Hall.

J. Turbomach 140(11), 111006 (Oct 10, 2018) (12 pages) Paper No: TURBO-18-1156; doi: 10.1115/1.4041400 History: Received July 12, 2018; Revised September 05, 2018

Unshrouded industrial centrifugal compressor impellers operate at high rotational speeds and volume flow rates. Under such conditions, the main impeller blade excitation is dominated by high frequency interaction with stationary parts, i.e., vaned diffusers or inlet guide vanes (IGVs). However, at severe part load operating conditions, sub-synchronous rotating flow phenomena (rotating stall) can occur and cause resonant blade vibration with significant dynamic (von-Mises) stress in the impeller blades. To ensure high aerodynamic performance and mechanical integrity, part load conditions must be taken into account in the aeromechanical design process via computational fluid dynamics (CFD) and finite element method (FEM) analyzes anchored by experimental verification. The experimental description and quantification of unsteady interaction between rotating stall cells and an unshrouded centrifugal compression stage in two different full scale compression units by Jenny and Bidaut (“Experimental Determination of Mechanical Stress Induced by Rotating Stall in Unshrouded Impellers of Centrifugal Compressors”, ASME J. Turbomach. 2016; 139(3):031011-031011-10) were reproduced in a scaled model test facility to enhance the understanding of the fluid–structure interaction (FSI) mechanisms and to improve design guide lines. Measurements with strain gauges and time-resolved pressure transducers on the stationary and rotating parts at different positions identified similar rotating stall patterns and induced stress levels. Rotating stall cell induced resonant blade vibration was discovered for severe off-design operating conditions and the measured induced dynamic von-Mises stress peaked at 15% of the mechanical endurance limit of the impeller material. Unsteady full annulus CFD simulations predicted the same rotating stall pressure fluctuations as the measurements. The unsteady Reynold's Averaged Navier-Stokes simulations were then used in FEM FSI analyses to predict the stress induced by rotating stall and assess the aerodynamic damping of the corresponding impeller vibration mode shape. Excellent agreement with the measurements was obtained for the stall cell pressure amplitudes at various locations. The relative difference between measured and mean predicted stress from fluid–structure interaction was 17% when resonant blade vibration occurred. The computed aerodynamic damping was 27% higher compared to the measurement.

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References

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Figures

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Fig. 3

Pressure and strain gauge instrumentation on the impeller

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Fig. 4

Dynamic Von-Mises stress distribution on impeller blade for mode shapes 1, 2, 6, and 7

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Fig. 2

Measurement procedure to identify the operating conditions with resonant blade vibration

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Fig. 5

Cutaway view of the full annulus CFD computational domain

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Fig. 1

Casing pressure transducers positions in meridional and axial views

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Fig. 8

Dynamic strain (gauge A, see Fig. 3) during detailed ramps

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Fig. 9

Spectrogram of strain gauge A1 (see Fig. 3) during speed ramp

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Fig. 10

Interference diagram with speed lines for Ω = 22,770 RPM

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Fig. 11

Measured dynamic Von-Mises stress at gauge A1 during speed ramp

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Fig. 12

Experimental determination (half-power method) of total damping (aerodynamic and material)

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Fig. 6

Meshed FE model (strain gauge locations A and B according to Fig. 3, are highlighted)

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Fig. 7

Rotating stall configurations inside the part load region of the measured compressor stage map (data from sensors 2M, see Fig. 1)

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Fig. 17

Dynamic Von-Mises stress distribution (mode 1, ND 6, maximum over phase) obtained from an FEM harmonic analysis with imposed EO9 pressure field

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Fig. 13

Predicted radial velocity field showing three stationary stalled diffuser regions (A) and nonstalled passages (B)

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Fig. 14

Measured and predicted pressure signals of the blade pressure side sensor K5 at the blade leading edge (see Fig. 3)

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Fig. 15

Measured and predicted casing pressure at sensor 2M2 (see Fig. 1) for impeller and cell rotation

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Fig. 16

Frequency response of normalized tangential blade tip displacement obtained from an FEM harmonic analysis with imposed EO9 pressure field

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Fig. 18

Predicted aerodynamic damping for (a) the entire impeller and (b), (c) two triplets of blades on the same nodal diameter over one impeller rotation

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