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Research Papers

Study of the Flow in a Vaneless Diffuser at Part Speed Operating Conditions

[+] Author and Article Information
Hamid R. Hazby

e-mail: h.hazby@pcaeng.co.uk

Liping Xu

e-mail: lpx1@cam.ac.uk
Whittle Laboratory,
Cambridge CB3 0DY, UK

Matthias Schleer

Siemens Turbomachinery Equipment GmbH,
Hessheimer Str. 2,
Frankenthal (Pfalz) 67227, Germany
e-mail: matthias.schleer@siemens.com

1Corresponding author.

Present address: PCA Engineers LTD., Lincoln, UK.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received April 23, 2013; final manuscript received May 17, 2013; published online September 26, 2013. Editor: David Wisler.

J. Turbomach 136(3), 031011 (Sep 26, 2013) (9 pages) Paper No: TURBO-13-1063; doi: 10.1115/1.4024693 History: Received April 23, 2013; Revised May 17, 2013

The aim of the current paper is to investigate the evolution of the flow in the vaneless diffuser of a scaled-up turbocharger compressor using the steady-state viscous calculations. First, the predicted flow patterns are compared with the detailed laser Doppler anemometry (LDA) and probe measurements acquired at different operating conditions. Then, the numerical results are analyzed further to understand the origins of the flow features observed in the measurements. It is shown that, despite the complexity of the flow, the main flow features in the vaneless diffuser can be predicted by computational fluid dynamics (CFD) at different operating conditions using a simple mixing length turbulence model. It is also demonstrated that, in the compressor studied, a vortical flow feature develops near the diffuser shroud at high flow coefficients. This flow feature is generated by strong pressure variations downstream of the impeller trailing edge and disappears at low flow coefficients, where the static pressure gradient becomes almost radial in the vaneless diffuser.

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References

Figures

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Fig. 2

Measured and predicted stage performances

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Fig. 3

Measured and predicted contours of radial and tangential velocities at 105% of the impeller exit radius at the design flow coefficient

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Fig. 4

Measured and predicted contours of radial and tangential velocities at 116% of the impeller exit radius at the design flow coefficient

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Fig. 1

Topology of the mesh at the tip section and blade trailing edge

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Fig. 5

Measured and predicted contours of radial and tangential velocities at 15% of the diffuser height (near the hub) at the design flow coefficient

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Fig. 6

Measured and predicted contours of radial and tangential velocities at 50% of the diffuser height (midheight) at the design flow coefficient

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Fig. 7

Measured and predicted contours of radial and tangential velocities at 90% of the diffuser height (near the casing) at the design flow coefficient

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Fig. 8

Contours of radial velocity at 105% of the impeller exit radius at different flow coefficients

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Fig. 9

Contours of absolute tangential velocity at 105% of the impeller exit radius at different flow coefficients

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Fig. 10

Contours of normalized total pressure at 105% of the impeller exit radius at different flow coefficients

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Fig. 11

Contours of absolute tangential velocity and vectors of relative velocity near the blade trailing edge

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Fig. 15

Radial and tangential forces exerted on the flow in the vaneless diffuser at midpassage (ϕ = 0.051)

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Fig. 16

Relative flow streamlines downstream of the impeller (ϕ = 0.022)

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Fig. 17

Contours of predicted static on the casing at different flow coefficients

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Fig. 18

Contours of relative Mach number at 105% of the impeller exit radius at different flow coefficients

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Fig. 12

Flow streamlines of impeller tip flow

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Fig. 13

Flow streamlines released in region “d”

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Fig. 14

Relative flow streamlines downstream of the impeller (ϕ = 0.051)

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