Research Papers

Large Eddy Simulation of the Unsteady Flow in a Radial Compressor Operating Near Surge

[+] Author and Article Information
Fredrik Hellstrom1

Department of Mechanics, The Royal Institute of Technology, SE 100 44 Stockholm, Swedenfredrik.hellstrom@mech.kth.se

Ephraim Gutmark

Department of Aerospace Engineeringand Engineering Mechanics,  University of Cincinnati, 799 Rhodes Hall, Cincinnati, OH 45221-0070ephraim.gutmark@uc.edu

Laszlo Fuchs

Department of Mechanics,  The Royal Institute of Technology, SE-100 44 Stockholm, Swedenlf@mech.kth.se


Address all correspondence to this author.

J. Turbomach 134(5), 051006 (May 08, 2012) (10 pages) doi:10.1115/1.4003816 History: Received June 21, 2010; Revised February 18, 2011; Published May 08, 2012; Online May 08, 2012

The flow in a centrifugal compressor has been computed using large eddy simulation (LES). The investigated geometry is that of a ported shroud compressor with a 10 blade impeller with an exducer diameter of 88 mm. The computational data compares favorably with measured data for the same compressor and operational point. For the considered operational point near surge, the flow field in the entire compressor stage is unsteady. Back-flow occurs in the diffuser, wheel, and the ported shroud channels resulting in back-flow at the walls in the inlet region of the compressor. In the diffuser and volute, the flow is highly unsteady with perturbations that are convected around the volute, affecting the flow field in most of the entire compressor. The mechanism driving this unsteadiness is assessed by flow visualizations, frequency analysis, and correlations of pressure and velocity data in order to gain a more comprehensive understanding of the mechanism leading to stall and surge.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

The geometry of the compressor and the compressor wheel. The black arrow in the top figure shows the recirculating flow in the ported shroud.

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Figure 2

The computational domain

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Figure 3

The measured compressor map with the computed operational point marked by X

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Figure 4

Time mean velocity magnitude in a plane passing along the axis of the shaft

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Figure 5

The time mean axial velocity in plane B just upstream of the leading edge of the blades. The position of the tongue is marked with a dot

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Figure 6

The time mean pressure distribution in the diffuser and volute (Plane C)

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Figure 7

The area averaged pressure in the outlet pipe at a position between the volute and the outlet boundary

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Figure 8

Snapshot of velocity in the inducer, wheel, and diffuser in the center axial plane

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Figure 9

Snapshot of velocity in the inducer (Plane A). The vector field shows the in-plane velocity colored with the ratio between the secondary flow and the axial velocity component

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Figure 10

Snapshot of the axial velocity component just upstream of the wheel (Plane B)

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Figure 11

Isosurface of instantaneous λ2 [22] in the compressor wheel

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Figure 12

Snapshots of the pressure field in the diffuser (Plane C) at three different time instants

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Figure 13

Snapshots of the velocity field in the diffuser (Plane C) at three different time instants

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Figure 14

Snapshot of the velocity field at the tongue

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Figure 15

Snapshot of the velocity field in the diffuser at twelve o’clock. The blade tip is located at the bottom of the figure.

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Figure 16

Cross correlation between two points in the volute and in the outlet pipe. The cross correlation for the points in the volute is marked with Δt11 and Δt12 (red) in the lower figure. The cross correlation for the points in the outlet pipe is marked with Δt21 and Δt22 (black). The probes in the volute are located at 6 o’clock and at 11 o’clock, respectively. In the outlet pipe, the first probe is located in the interface between the volute and outlet pipe and the second probe is located 140 mm downstream of the first probe.

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Figure 17

The frequency spectra of the pressure signal from one point in the volute (black) and one point in the outlet pipe (red). The frequency spectra with a peak at 300 Hz is from the point in the volute. The probe in the volute is located at six o’clock in the volute and the probe in the outlet pipe is located in between the volute and the outlet of the pipe.

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Figure 18

A sketch of the propagating directions for pressure waves in the wheel, diffuser, volute, and outlet pipe




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