Transcript Diapositive 1 - Polytechnic of Namibia

A study of the Butterfly-Effect for Massively
Separated Flows using OpenFOAM®
Dr. Alexander Michalski, SL-Rasch GmbH
Dr. Ries Bouwman, ESI Group
7th OpenFOAM Workshop
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2012 All
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reserved.
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SL Rasch
Architects
Specialised in special buildings and lightweight structures
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2
ESI Worldwide Operations
Headquarters in Paris,
France
Offices in more than 30
countries
Average Headcount:
+900 people
Over 200 Scientists
WW Revenue 2010:
~100 M€
Paris, France
Eschborn, Germany
Pilsen, Czech Republic
Farmington Hills, MI
Beijing, China
Tokyo, Japan
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3
Virtual Try-Out Space
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Setup - Model
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Setup – Inlet Profile
A wind-type velocity profile was applied at the inlet, with a law of:
v(z) = 21.1 (z/10)^0.26, in m/s
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Setup – Post-Processing
11 points were monitored:
• 3 points 5 meters upstream of
the cube, at +/-20m and 0 in
Y, and at 30m in Z.
• 4 points 5m downstream of
the cube, at +/-5m and +/-15m
in Y, and at 30m in Z.
• 4 points upstream of umbrella
at 60m in X, at +/-5m and +/15m in Y, and at 31m in Z.
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PAM-FLOW
Physics:
Compressible and incompressible NS solver (transient and steady flow)
Turbulence models: Smagorinsky SGS (LES), K-epsilon, Spalart-Almaras, BaldwinLomax
Law of the wall or no-slip walls (with semi-structured boundary layer mesh)
Moving bodies (6-DOF rigid bodies, FSI)
Boundary fitted model: ALE grid and automatic remeshing
Embedded mesh
Highly accurate numerical schemes, both in time and space
Spatial discretisation: Edge-based finite-element and explicit/implicit NS solver, Adaptive
mesh refinement
Temporal discretisation: Explicit schemes (compressible flow), Implicit pressure projection
explicit scheme (incompressible), Implicit matrix free LU-SGS (compressible and
incompressible flow)
DMP and SMP (hybrid) parallel runs.
FSI: MPI coupling with VPS (PAM-CRASH)
Main applications: Aeroacoustic sources characterization, Fluid
Structure Interaction
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Original Study PAM-FLOW
Same mesh, different number of domains
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Original Study PAM-FLOW
Different meshes
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Original Study PAM-FLOW
Conclusions
For different number of domains, very small differences at
beginning of run grow progressively to state of total dissimilitude
Actual (deterministic) instantiation completely different
Mean loads remain similar
Upstream of cube no differences
Butterfly Effect
Even very small (roundoff) errors can have a pronounced effect
on actual deterministic instantiation of a flowfield
Important if mean flow field is less important than
actual (maximum) field
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OpenFOAM
High quality mesh generated using VisCART
ESI proprietary cartesian automatic mesher
snappyHexMesh not sufficient quality for umbrella structure
Simulation performed with OpenFOAM 2.1
On RedHat Linux
LES
Smagorinsky Subgrid Scale model
1.800 sec real time, time step of 5msec
Max Courant number of 2.0
Flow field initialised from a static flow
0 m/s in all directions
Simulation was done with 3 SIMPLE partitions in X-Y-Z
8 cores: coefficients 4-2-1
32 cores: coefficients 16-2-1
64 cores: coefficients 32-2-1 in X-Y-Z)
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VisCART mesh
Total Mesh size: 910k cells
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OpenFOAM Study
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OpenFOAM Study
15 s
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OpenFOAM Study
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OpenFOAM Study
Although the instantaneous forces/moments as well as flow pictures
are different, the average flow fields are very similar.
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Conclusion
Same effect seen with OpenFOAM as with PAMFLOW
Irrespective of wind data
Irrespective of transient or steady state run
Effect depends on number of domains
Effect depends on memory preconditioner
Reason:
inner products of very long vectors that are distributed among
domains are required
Order for required additions affects iterative solver
Leads to different instantiations with different number of domains
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FLUENT Study
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