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Research Papers: Multiphase Flows

Numerical Simulation of 3D Cavitating Flows: Analysis of Cavitation Head Drop in Turbomachinery

[+] Author and Article Information
Benoît Pouffary

 Centre National d’Etudes Spatiales, Evry, 91023 France

Regiane Fortes Patella

 INPG-LEGI, Grenoble, 38041 France

Jean-Luc Reboud

CNRS-G2ELAB, University of Grenoble, Grenoble, 38042 France

Pierre-Alain Lambert

 Snecma, Vernon, 27208 France

J. Fluids Eng 130(6), 061301 (May 19, 2008) (10 pages) doi:10.1115/1.2917420 History: Received September 08, 2005; Revised March 12, 2008; Published May 19, 2008

The numerical simulation of cavitating flows in turbomachinery is studied at the Turbomachinery and Cavitation team of Laboratoire des Ecoulements Géophysiques et Industriels (LEGI), Grenoble, France in collaboration with the French space agency (Centre National d’Etudes Spatiales, CNES), the rocket engine division of Snecma and Numeca International. A barotropic state law is proposed to model the cavitation phenomenon and this model has been integrated in the CFD code FINE/TURBO ™. An analysis methodology allowing the numerical simulation of the head drop induced by the development of cavitation in cold water was proposed and applied in the case of two four-bladed inducers and one centrifugal pump. Global results were compared to available experimental results. Internal flows in turbomachinery were investigated in depth. Numerical simulations enabled the characterization of the mechanisms leading to the head drop and the visualization of the effects of the development of cavitation on internal flows.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Graph of the barotropic state law ρ=ρ(P). Illustration of the speed of sound influence for water at 20°C. For more information, see Ref. 8.

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Figure 2

Mesh of the SHF centrifugal pump

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Figure 3

Inducer geometries: (a) Inducer 1; (b) Inducer 2

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Figure 4

Inducer 1 shroud static pressure at nominal flow rate (blue triangles, measurements; red rhombus, computation; k-ε+wall functions). Noncavitating condition. Meridian coordinate is nondimensional.

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Figure 5

SHF centrifugal pump, nominal flow rate, for decreasing NPSH=(Pref-Pv)∕(ρg)≈9.5m, 7m, and 6.3m. The yellow color corresponds to a 5% equivalent void ratio. Comparison experiment/calculation of the suction side cavity extension. Experimental visualizations by Electricité de France (26).

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Figure 6

Cavitation head drop curves at different flow rates

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Figure 7

Nominal flow rate. Evolution of mechanical and hydraulic power calculated; mechanical power=Tω hydraulic power=ΔPtot.Q.

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Figure 8

Nominal flow rate. Blade load at midspan, for decreasing NPSH ≈15m, 9.5m, 7m, and 6.3m (with about 7% total head drop).

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Figure 9

Location of the analyzed flow sections in the SHF pump

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Figure 10

Repartition of the total pressure rise between Sections 1 and VIII of the SHF pump, in noncavitating conditions (nc: left) and with decreasing downstream cavitation numbers (1–6). Total pressures are evaluated by mass-flow averaging in the cut plane. As the NPSH is calculated a posteriori from the upstream pressure resulting from the cavitating flow simulation, it takes into account the decreasing pump head associated with cavitation breakdown. The last four NPSH values, during final head drop, are found nearly constant, whereas the net downstream pressure continues to be decreased.

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Figure 11

(a) Secondary flows: Dimensionless relative helicity, varying from −1 (blue, maximum anticlockwise vorticity) to 1 (red, maximum clockwise vorticity). Noncavitating flow. Planes I to IV. (b) Secondary flows (dimensionless relative helicity). Cavitating flow corresponding to 7% total head decrease. Planes I to IV.

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Figure 12

Inducer 1, nominal flow rate, for decreasing cavitation number. The blue color corresponds to a 5% equivalent void ratio. Upstream cavitation numbers: (a) 0.0196; (b) 0.016; (c) 0.014; (d) 0.012.

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Figure 20

Repartition of the total pressure rise between Sections “a”–“f” of Inducer 2, in noncavitating condition (nc: left) and with decreasing downstream cavitation numbers (1–7). Total pressures are evaluated by mass-flow averaging in the cut plane. Sections “a”–“f” locations are presented in Fig. 2.

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Figure 19

Nominal flow rate. Inducer 2. Blade load at mid span, for decreasing cavitation numbers.

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Figure 21

Illustration of Planes “a”–“f” in the meridian view of Inducer 2

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Figure 18

Cavitation head drop curve. Nominal flow rate, Inducer 2.

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Figure 17

Inducer 2, nominal flow rate, for decreasing upstream cavitation numbers: (a) 0.12; (b) 0.08; (c) 0.05; (d) 0.03. The blue color corresponds to a 5% equivalent void ratio.

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Figure 16

Secondary flows (dimensionless relative helicity), and noncavitating (a) and cavitating (b) flows. Planes I and II.

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Figure 15

Repartition of the total pressure rise between Sections “a” and “h” of Inducer 1, in noncavitating conditions (nc: left) and with decreasing downstream cavitation numbers (1–8). Total pressures are evaluated by mass-flow averaging in the cut plane. Sections “a”–“h” are perpendicular to the axial direction, as schematized in Fig. 2 for the Inducer 2 geometry. As in Fig. 1, the last two upstream cavitation number values are found nearly constant for decreasing values of the downstream cavitation number.

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Figure 14

Nominal flow rate. Inducer 1. Blade load at midspan, for decreasing cavitation numbers.

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Figure 13

Cavitation head drop curves at nominal flow rates. Comparisons between computations and experiments performed at the CREMHyG Laboratory (upstream cavitation number).

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