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Research Papers

Design and Testing of Multistage Centrifugal Compressors With Small Diffusion Ratios

[+] Author and Article Information
C. Aalburg

 GE Global Research, 85748 Garching, Munich, Germanychristian.aalburg@research.ge.com

A. Simpson, M. B. Schmitz

 GE Global Research, 85748 Garching, Munich, Germany

V. Michelassi, S. Evangelisti, E. Belardini, V. Ballarini

 GE Oil & Gas, 50127 Florence, Italy

J. Turbomach 134(4), 041019 (Jul 25, 2011) (8 pages) doi:10.1115/1.4003715 History: Received October 18, 2010; Revised January 24, 2011; Published July 25, 2011; Online July 25, 2011

Two stators of a multistage centrifugal compressor with progressively smaller outer radii have been designed, built, and tested. The aim was to achieve a significant reduction in the outer diameter of the compressor stage without compromising performance. The reduction in size was achieved by reducing the diffusion ratio (outer radius/inner radius) of the vaneless diffuser in two steps. In the first step, the outer diameter of the entire stage was reduced by 8% compared with the baseline design. In the second stage, the outer diameter was reduced by 14%. The outer radius of the smallest design was limited by the impeller exit diameter, which was kept constant, as was the axial length of the stage. The large radius baseline design has been tested on a rotating rig in a 1.5 stage setup. This setup aimed at simulating the multistage behavior by applying a pseudostage upstream of the main stage. The pseudostage consisted of a set of nonrotating preswirl vanes in order to mimic an upstream impeller and was followed by a scaled version of the return channel of the main stage. The experimental database was then used to calibrate a 1D analysis code and 3D–computational fluid dynamics methods for the ensuing design and optimization part. By applying an extensive design-of-experiments, the endwalls as well as the vanes of the stator part were optimized for maximum efficiency and operation range. In order to preserve the multistage performance, the optimization was constrained by keeping the circumferentially averaged spanwise flow profiles at the exit of the smaller radius stages within close limits to the original design. The reduced radius designs were then tested in the same 1.5 stage setup as the baseline design. The results indicate that the reduction in size was feasible without compromising the efficiency and operation range of the stage.

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Figures

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Figure 1

Schematic of the test configuration with measurement planes used throughout the experiments

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Figure 2

Schematic of numerical setup used during the optimization phase of the statoric components

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Figure 3

Schematic of the stator part with three different diffusion ratios

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Figure 4

One-dimensional predictions of loss coefficients of the diffuser, bend, and return channel. In all cases, the loss coefficients are normalized by the dynamic pressure at the diffuser inlet.

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Figure 5

Flow down chart for the design of the return channel

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Figure 6

Measured polytropic stage efficiency and impeller work coefficient as a function of flow coefficient for three diffusion ratios, 1.45BL, 1.30A, and 1.19A at Mach number M=0.7. Please note that 1.30A was tested with two different measurement resolutions.

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Figure 7

Circumferentially area averaged profiles of normalized total pressure at the top of the bend (left) and corresponding yaw angles at the leading edge of the return channel vane (right) as a function of spanwise position. Shown are measurements and predictions based on constant turbulence intensity and turbulence length scales ranging from 0.02 to 0.16 times passage width at the diffuser inlet.

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Figure 8

Measured and predicted polytropic stage efficiencies and impeller work coefficient as a function of flow coefficient for diffusion ratios 1.45BL, 1.30A, and 1.30B, the latter both with baseline and matching pseudostage, all at constant impeller Mach number M=0.7

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Figure 9

Measured and predicted mass averaged yaw angles at the inlet and exit of the 1.30B stage for both baseline and matching pseudostage configuration

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Figure 10

Circumferentially mass averaged yaw angles as a function of spanwise position near design point. Shown are measurements and predictions at the inlet and exit of the 1.30B stage in baseline pseudostage configuration and predictions at stage exit of the reference 1.45BL stage.

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Figure 11

Circumferentially mass averaged total velocities normalized by the average total velocity as a function of spanwise position near design point. Shown are measurements and predictions at inlet and exit of the 1.30B stage in baseline pseudostage configuration and predictions at stage exit of the reference 1.45BL stage.

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Figure 12

Measurements of circumferentially mass averaged yaw angles and prescribed values used during the second design optimization as a function of spanwise position immediately after the impeller of the 1.30B stage near design point

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