LARGE EDDY SIMULATION OF CAVITATING PROPELLER FLOWS 1 Chalmers - - PowerPoint PPT Presentation

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large eddy simulation of cavitating propeller flows
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LARGE EDDY SIMULATION OF CAVITATING PROPELLER FLOWS 1 Chalmers - - PowerPoint PPT Presentation

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Shipping and Marine Technology Computational Hydrodynamics Tobias Huuva 1,2 , Rickard Bensow 1 , Gran Bark 1 , LARGE EDDY SIMULATION OF CAVITATING PROPELLER FLOWS 1 Chalmers University of Technology, 2 Berg Propulsion Technology AB SIAMUF

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SLIDE 1

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

LARGE EDDY SIMULATION OF CAVITATING PROPELLER FLOWS

Tobias Huuva1,2, Rickard Bensow1, Göran Bark1,

1 Chalmers University of Technology, 2 Berg Propulsion Technology AB

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SLIDE 2

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

Background

Requirements for numerical cavitation erosion predictions?

  • Which cavitation mechanism are necessary to

include?

– Side and re-entrant jets – Importance of viscosity – Cloud formation – …

  • Computational requirements?

– RANS vs. LES – Mesh resolution – Compressibility – …

Supported by experimental observations (EROCAV, Virtue) Supported by workshops, project meetings, private communication

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SLIDE 3

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

Modeling approach

Incompressible, viscous LES with VoF

– Probably beneficial to take compressibility into account

  • Solver stability, physical modeling, pressure pulse prediction

– LES natural choice for cavitating flows

  • Inherently unsteady
  • Difference in computational cost compared with RANS not that

large

– Physics require fine resolution in time and space

  • Prospect of high frequency phenomena

– Single fluid two-phase mixture works well with filtering in LES – Unstructured grids (Propeller)

  • Local grid refinement necessary

– Mass transfer model (“cavitation model”)

  • Less important than flow solver choices

Time average Instantaneous

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SLIDE 4

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

Computational Configuration

– ILES in mixed formulation

  • 2nd order backward differencing in time

– Δt ≈ 2e-6

  • CD with limiter for convective terms
  • PISO

– Mixed fluid – vapor/liquid

  • VoF-approach
  • Transport equation for vapor fraction α

– Mass transfer modeling following Kunz

  • A+=1e6, A-=1e3, ρl/ρv=1000 with1

– OpenFOAM

  • Open source CFD library tools

1 Huuva et al., IAHR symp. 2007 Huuva, PhD-thesis, 2008

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SLIDE 5

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

LES Modeling

– Mixed formulation1 – Implicit modeling

  • Physical dissipation represented by numerical dissipation
  • Flux limiting, dissipative numerical scheme

– Wall modeling2

  • Law-of-the-wall based
  • Adjust viscosity to account for wall effects
  • Used both with explicit and

implicit approaches

  • Extensively tested

1 Bensow & Fureby, J. Turbulence 8:54, 2007 2 Fureby et al. AIAA J. 2004

( ) ( ) ( )

  • =
  • +
  • +
  • +
  • =

+ +

  • B

v v v v v v v v v v v v v v v v L C R % % % B= v

v

v

v

( )

+ v v + v v

( )+

  • v

v

( )

=L+C+R

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SLIDE 6

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

Propeller flow validation

  • Non-cavitating, homogenous inflow

– J=0.88: U∞=5 m/s, 25 rps1 – J=0.71: U∞=5.808 m/s, 36 rps – DP=0.227 m

Experiments by DiFelice et al., ||curl(U)||=75 J KT 10KQ η 0.88 Exp 0.157 0.306 0.719 ILES 0.158 0.308 0.718 MixedILES 0.157 0.308 0.714 MixedILES (limitedLinear) 0.159 0.307 0.725 MixedILES (no WM) 0.159 0.316 0.704 OEEVM 0.150 0.317 0.663 MixedOEEVM 0.153 0.320 0.668 0.71 Exp 0.256 0.464 0.623 MixedILES (limitedLinear) 0.256 0.453 0.639

1 Bensow & Liefvendahl AIAA 38th Fluid Dyn., 2008

– 4.8M cells, tets+prisms – Refined in tip vortex and blade wake regions

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SLIDE 7

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

Propeller flow validation

Normalized axial velocity @ x/RP=0.65 r/RP=0.25, 0.7, 0.95, 1.05

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SLIDE 8

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

Delft Twist11 Foil

  • NACA009 with varying aoa, -2° to 9°
  • Similar to propeller blade root section
  • Unsteady cavitation in

homogeneous inflow

  • U∞=6.97 m/s, σ=1.07, LC=0.15m
  • 2.2M cells, hex, half domain

Experiments by Foeth et al.

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SLIDE 9

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

Delft Twist11 Foil, cont’…

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SLIDE 10

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

Cavitating E779A Propeller in Open Water

  • J=0.71, σn=1.76

– U∞=5.808 m/s, 36 rps, DP=0.227 m

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SLIDE 11

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

E779A in Artificial Wake

  • J=0.90, σn=4.455

– U∞=6.22 m/s, 30.5 rps, DP=0.227 m – Grid with 4.6 M cells, tets+prisms, locally refined in sheet cavity region

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SLIDE 12

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

Cavitation Dynamics

Experiments by Pereira et al.

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SLIDE 13

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

Cavitation Dynamics

Experiments by Pereira et al.

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SLIDE 14

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

Tip Vortex/Cavity interaction

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SLIDE 15

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

Conclusions

  • Possible to simulate some mechanisms of dynamic

cavitation

– Detect initial condition for erosive cavitation – Mesh resolution needs to be finer to trace shed cavities – Room for improvement in modeling but not essential – May soon be used for advanced design considerations

  • Numerical methods and physical modeling tightly

coupled

– These results are not credited to a single isolated factor (LES, Kunz, parameter settings etc.)

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SLIDE 16

Shipping and Marine Technology

Computational Hydrodynamics

SIAMUF

12-13 May 2009, Älvkarleby

tobias.huuva@bergpropulsion.com

Thanks for your attention! Questions and comments!

Tobias Huuva

tobias.huuva@bergpropulsion.com