Flow through and around groups of bodies Door vortex Andre Nicolle - - PowerPoint PPT Presentation

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Flow through and around groups of bodies Door vortex Andre Nicolle & Ian Eames As the complexity of a bounding geometry increases, at some stage we need a reduced modelling approach. To understand the salient aspects of the flow and

SLIDE 1

Flow through and around groups of bodies

Andre Nicolle & Ian Eames

t = 34 s t = 6 s Door vortex

As the complexity of a bounding geometry increases, at some stage we need a reduced modelling approach. To understand the salient aspects of the flow and physics we need to study in detail what happens as the number of bodies (or the complexity of the domain) increases. This provides a means to test reduced (ie simple) mathematical models.

Eames (Ed) 2008 Themed vol on New Perspectives on Dispersed Multiphase

Flows. Phil Trans.

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Physical processes

Flow past isolated and multiple bodies

Point force representation

Vorticity annihilation

Magnaudet & Eames 2000 Ann Rev Fluid Mech Hunt & Eames 2005 JFM

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We developed a parallel computational code, written in C++ using late binding object orientated method and high performance numerical libraries (PETSc, Intel MKL and MPI, ParMETIS, TetGen), was developed. The numerical method was validated against standard test cases on a small cluster before running high resolution simulations on Legion. The code is capable of fully resolving 2-D and 3-D fixed domains and domains on which surfaces move and deform. We used an ALE-CBS-FEM formulation for solving the Navier-Stokes

equation. To ensure mesh quality was maintained, the domain was

continuously checked and adaptively remeshed if required.

Numerical calculations

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Configuration

Re=100 for individual cylinder, Re_G=2100 for group 5-6 million nodes / run time about 6 days on 32 CPU or 18 hrs for 256 CPU’s (on Legion)

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Modelling approach

Add together the inviscid and viscous contributions Could be adapted to include vortex shedding by fluctuating drag / lift force. Use of integral constraints.

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Flow past isolated and multiple bodies

N=7 N=20 N=39 N=95 N=133

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Individual wakes in near field Flow shedding from isolated cylinder Large shear layer

Flow past isolated and multiple bodies

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Case 1

S1 N=1

Case 2

Case 1

Maximum vorticity downstream

Case 1 Case 1

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Case 1

Maximum vorticity downstream

Case 3

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Average flow through the array

Average velocity in array. Downstream, it is more useful to apply conditionally averaged approach (eg Hunt, Eames & Westerweel 2004 JFM; Eames & Flor 2010 Phil Trans Themed vol)

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Integral measures of flow in array

Eulerian average velocity average Lagrangian velocity

Eames, Hunt & Belcher 2005 JFM

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Experimental study

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Conclusion

1. For high void fractions (>0.1), an average drag model is suitable

but the difficulty is to choose the drag closure.

2. Flow low void fractions, the effects of individual bodies needs to

described.

3. Both kinematic blocking and wake effects important and can be

described in a simple manner.

Ratio of wake length to array size

Inviscid blocking important distributed drag models

void fraction

Individual bodies need to be modelled Inviscid blocking weak Eames, Roig, Hunt & Belcher 2006 NATO