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Research Papers

Unsteady Computational Fluid Dynamics Investigation on Inlet Distortion in a Centrifugal Compressor

[+] Author and Article Information
Armin Zemp

Laboratory for Energy Conversion (LEC), Department of Mechanical and Process Engineering, ETH Zurich, Zurich 8092, Switzerlandzemp@lsm.iet.mavt.ethz.ch

Albert Kammerer, Reza S. Abhari

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

J. Turbomach 132(3), 031015 (Apr 02, 2010) (9 pages) doi:10.1115/1.3147104 History: Received August 25, 2008; Revised September 09, 2008; Published April 02, 2010; Online April 02, 2010

Blade failure in turbomachinery is frequently caused by an excessive resonant response. Forced response of the blades originates from unsteady fluid structure interactions as conditioned in the inlet section by duct bends, struts, or inlet guide vanes. This paper presents the computational part of a research effort that focuses on the blade forced response in a centrifugal compressor. Unsteady fluid flow simulations are used to quantify the forcing function acting on the compressor blades due to inlet flow distortion. The measured inlet flow distribution is applied as inlet boundary conditions in the computation. The unsteady investigation provided the temporal evolution of the distorted flow through the compressor. The time-resolved blade pressure distribution showed the temporal evolution of the dynamic load on the blade surface caused by the inlet distortion. The results suggest that the forcing function is most sensitive in the leading edge region due to inlet angle variations. Toward the impeller stability line the increase in incidence caused separation on the suction side of the main blade and therefore considerably altered the amplitude and the phase angle of the unsteadiness. The investigation of the effect of idealizing the inlet flow distribution on the forcing function showed an increase in the peak amplitude of approximately 30% compared with the actual inlet flow distribution.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 2

Measured inlet total pressure distribution p0/p01

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Figure 3

Interpolated and idealized inlet total pressure boundary condition p0/p01

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Figure 4

Campbell diagram of impeller main blade

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Figure 5

Compressor map A8C41 impeller

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Figure 6

Total pressure ratio (Mu=0.8 and Q/Qref=0.55) at impeller exit: (a) computational and (b) experimental

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Figure 7

Relative difference in total pressure ratio: numerical results compared with FRAP measurements (Mu=0.8 and Q/Qref=0.55)

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Figure 8

Monitoring points on main blade surface

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Figure 9

Evolution of correlation coefficient in unsteady simulation

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Figure 10

Comparison of computed performance, 16,250 rpm, 5. EO distortion

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Figure 11

Total pressure profiles, hub to shroud, impeller exit, 16,250 rpm, Q/Qref=0.62, 5. EO distortion

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Figure 12

Relative total pressure at midspan

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Figure 13

Path-time diagram, pressure fluctuation (PS-SS), midspan, 5. EO, 16,250 rpm, Q/Qref=0.76

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Figure 14

FFT amplitude of unsteady pressure on PS of MB, 16,250 rpm, Q/Qref=0.76, midspan

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Figure 1

Impeller and computational domain

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Figure 15

FFT amplitude [Δp′], fundamental excitation, 16,250 rpm, Q/Qref=0.76, hub to shroud variation

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Figure 16

FFT phase angle (deg), fundamental excitation, 16,250 rpm, Q/Qref=0.76, hub to shroud variation

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Figure 17

FFT amplitude [Δp′], midspan, 5. EO, 16,250 rpm, variable mass flow rate

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Figure 18

FFT phase angle (deg), midspan, 5. EO, 16,250 rpm, variable mass flow rate

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Figure 19

prms′, main blade, inducer section

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Figure 20

Incidence angles, midspan, main blade, 16,250 rpm, 5. EO

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Figure 21

Real inlet total pressure boundary condition distribution p0/p01, 5. EO

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Figure 22

FFT amplitude of unsteady pressure on PS at midspan, 16,250 rpm, Q/Qref=0.76, real inlet total pressure boundary condition distribution

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Figure 23

FFT amplitude [Δp′], midspan, 16,250 rpm, 5. EO, Q/Qref=0.76, idealized versus real inlet total pressure boundary conditions

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