EdF meeting 18 May 2009
Review of all the work done under the framework of
Code_Saturneby
S. Rolfo
School of Mechanical, Aerospace & Civil Engineering (MACE)
The University of Manchester
Manchester, M60 1QD
www.CFDtm.org
Summary
Use of unstructured meshes in Code_Saturne: Taylor Green vortices Laminar Channel flow
Developments: Hybrid RANS/LES Calculation of statistics: store of gradients (need only
feedback)
Refined LES of flow in fuel rod bundle arranged into a triangular array
Sodium Fast Reactors (SFR) fuel bundles.
Energy conservation: Taylor-Green vortices test case.
)22cos()2cos(4
1
)sin()cos(
)cos()sin(
1
212
211
kxkxp
kxkxu
kxkxu
20
20
ij j
jL2
jj
φ (x) φ (x)
err =φ (x)
Taylor-Green vortices test case: mesh generation.
Resolution: 60 x 60
Time step: 0.01 => CFLmax < 0.2
RR=ABAC
Effects of different Refinements Ratio (RR)
Effects of different Refinements Ratio (RR)
Refinements 1-2 optimization.
Map of 1-2 optimization
Example of optimization.
P1 P3
In terms of energy conservation the tilting is not producing the best results.The best results are obtained keeping the interface flat. Moving the position of the interface does not affect to much the results.
Results optimization
Global error on U and dU/dx for different meshes
Error conformal mesh
Error RR=0.97 mesh
Error RR=0.75 mesh
Error RR=0.50 mesh (base)
Error RR=0.50 mesh (“optimal” P3)
Error Hybrid mesh poly+hexa
Laminar channel flow poly mesh
Test of laminar flow at Ret=501. Mesh for Ret=395
1. N cells: 6390002. N Faces: 36600003. Different type of optimization, no big improvements (no reducing
of warping, skewing angle, etc)4. Interface prism/poly @ y+~100=>interface @ y=0.18
2. Mesh for Ret=10201. N cells: 35000002. N Faces: 205000003. Interface prism/poly @ y+=100=>interface @ y=0.1
In both the cases relatively big oscillation of V, W, P were found. Moreover the maximum velocity at the centre line was 20 or less.
(Ret=50 => Umax=25). This means a difficulty of the mesh to converge.
Laminar channel flow mesh 395 ( History)
Laminar channel flow mesh 395 (Profile)
Laminar channel flow mesh 1020 ( History)
Laminar channel flow mesh 1020 (Profile)
Rod Bundle arranged in a triangular array
Geometrical configuration: P/D = 1.06 Big computational
domain (7 mil cells)
Thermal Hydraulic regime Re=5994
Heat transfer (qw=60 W/m2)
New cases to run Re=5994 with imbalance
in the temperature Re=12000 (mesh ready
with 14 mil cells) Possible Higher P/D
Mean quantities
<U> <T>
Re stresses
<uu>
<vv>
<ww>
<uv>
<uw>
<vw>
Temperature
<θθ> <uθ>
<wθ><vθ>
Imbalance of temperature
28
SFR fuel assembly: Case presentation Flow parameters:• P/D = 1.1 • Re = 11000 (Bulk vel = 1 m/s)• Working fluid liquid sodium
• = 847 kg/m3• µ = 2.55 10-4 Kg/m/s• Pr = 5 10-3
SFR test case
SFR rod bundle
Future near work Calculation of the complete geometry with 271 pins (mesh ready, but
problem with some warp faces). Literature review on experimental paper of the same geometry with
different numbers of fuel elements.
Future work Extension of the 6 pin mesh in order to perform low Reynolds
calculations. Extension of the case to different number of pins and comparison of the
results with the available experiments Refined calculations: LES?!!
RANS-LES coupling (1)
The Hybrid RANS-LES method is following a usual LES decomposition in large scale and sub-grid part:
The anisotropic part of the residual stress tensor and residual heat flux can be decomposed following a Schumann decomposition:
Sub- grid viscosity
RANS viscosity computed from the mean velocity field
For the eddy conductivity a simply turbulent Prandtl number analogy is used
RANS-LES coupling (2)
The merging between the two velocity fields is done through a blending function to obtain a smooth transition
Turbulent RANS length scale computed with a relaxation model based on
Filter width
Empirical constants computed in order to match the stress profile for channel flow @ Re = 395
RANS-LES Results
Gradient calculation.
Gradient calculation and store in PROPCE Now available only for the velocity and version 1.4.0 Addition of pressure and temperature really straight forward Possible use to compute budgets , but extension in order to include
second order derivatives is necessary => huge number of properties will be stored
Need a feedback about the implementation in order to carry out the addition of all the others term.
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