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Research Papers

Effect of Unsteadiness on the Performance of a Transonic Centrifugal Compressor Stage

[+] Author and Article Information
Isabelle Trébinjac, Pascale Kulisa, Nicolas Bulot

Laboratoire de Mécanique des Fluides et d’Acoustique, UMR CNRS 5509, Ecole Centrale de Lyon, UCBLyon I, INSA 36 Avenue Guy de Collongue, 69134 Ecully Cedex, France

Nicolas Rochuon

TURBOMECA, Groupe SAFRAN, 64511 Bordes, France

J. Turbomach 131(4), 041011 (Jul 02, 2009) (9 pages) doi:10.1115/1.3070575 History: Received August 21, 2008; Revised September 10, 2008; Published July 02, 2009

Numerical and experimental investigations were conducted in a transonic centrifugal compressor stage composed of a backswept splittered unshrouded impeller and a vaned diffuser. The characteristic curves of the compressor stage resulting from the unsteady simulations and the experiments show a good agreement over the whole operating range. On the contrary, the total pressure ratio resulting from the steady simulations is clearly overestimated. A detailed analysis of the flow field at design operating point led to identify the physical mechanisms involved in the blade row interaction that underlie the observed shift in performance. Attention was focused on the deformation in shape of the vane bow shock wave due its interaction with the jet and wake flow structure emerging from the impeller. An analytical model is proposed to quantify the time-averaged effects of the associated entropy increase. The model is based on the calculation of the losses across a shock wave at various inlet Mach numbers corresponding to the moving of the jet and wake flow in front of the shock wave. The model was applied to the compressor stage performance calculated with the steady simulations. The resulting curve of the overall pressure ratio as a function of the mass flow is clearly shifted toward the unsteady results. The model, in particular, enhances the prediction of the choked mass flow.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

3D sketch of the centrifugal compressor stage

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Figure 2

Meridional view of the compressor stage

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Figure 3

H-C-O topology of the mesh

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Figure 4

Pressure ratio of the compressor stage

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Figure 5

Reduced temperature rise

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Figure 6

Level of unsteadiness through the impeller (a) and through the vaned diffuser (b)

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Figure 7

Reduced meridional velocity at section E (m∗=0.63)

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Figure 8

Reduced tangential velocity at section E (m∗=0.63)

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Figure 9

Purely unsteady relative velocity at mid inter-row gap and 70% section height, over a stator pitch and a rotor time-period

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Figure 10

Meridional evolution of entropy

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Figure 11

Absolute Mach number contours, at 50% section height

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Figure 12

Absolute Mach number, at 50% height

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Figure 13

Absolute normal Mach number, close to impeller exit

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Figure 14

Corrected pressure ratio of the compressor stage

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