CFD Analysis of Ribroughness Effects on Flow between Gas Reactor Fuel Pins

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CFD Analysis of Rib-roughness Effects on Flow
between Gas Reactor Fuel Pins
KNOO annual meeting University of Manchester
17/07/2008

• By
• Amir Keshmiri (WP1/WP4)
• Colleagues
• D.R. Laurence, M.A. Cotton, Y. Addad and S. Rolfo

School of Mechanical, Aerospace Civil
Engineering (MACE) The University of
Manchester Manchester M60 1QD
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Outline

• Introduction to AGRs
• Earlier Works
• The Problem Definition
• Various Rib Configurations
• Results of 2-Dimensional Transverse Ribs
• Effective Sand-Grain Roughness Method
• Results of 60o sector with Hoop Ribs
• Future Work
• Summary

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Advanced Gas-cooled Reactors (AGRs)
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Earlier Work
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Fuel Elements in Advanced Gas-cooled Reactors
(AGRs)
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Fuel Elements in Advanced Gas-cooled Reactors
(AGRs)
Transverse ribs

• Fuel Resistance
• Pressure Drop
• Optimisations

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Various Configurations

• Multi-start
• Transverse

3) Hoop 4) Smooth
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Input Data
General Working fluid CO2 Re1e6 based on
Dh Flow direction Upward Mass flow rates Fuel
channels 3910 kg/s Net circular flow 4270
kg/s Peak channel flow 15.3 kg/s
Working bulk temperatures Channel inlet 334oC
Channel outlet 635oC Peak Temp661oC
Working pressures inside pressure vessel Bottom
slab 45.2 bar Top slab and walls 42.5 bar

• The Safety of the AGR by J M Bowerman (1982)

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Transverse configuration
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Transverse configuration
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Transverse configuration
Velocity Vector
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2) Transverse configuration
Temperature Contour (as a passive scalar)
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Transverse configuration
Pressure Contour
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Transverse configuration
Leonardi et al. 2003, "DNS of turbulent channel
flow with transverse square bars on one wall"
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Effective Sand-Grain Roughness for Ribbed Surfaces
Drag Coefficient, cD 1.25
Darcy friction factor formula
Jimenez, J. 2004, Turbulent Flows over Rough
Walls, Annu. Rev. Fluid Mech., Vol. 36, pp.
173-196
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Hoop configuration
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Hoop configuration
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Hoop configuration
High Reynolds Number k-epsilon model Streamwise
Velocity Contour
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Hoop configuration
High Reynolds Number k-epsilon model
Temperature Contour
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Hoop configuration
High Reynolds Number k-epsilon model Pressure
Contour
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Future Work
Simulating fuel element with Multi-start design
120o sector is required to be meshed and
simulated due to different handed pins
Simulating smooth fuel elements and compare with
ribbed-designs
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Future Work
Test and compare different rib profiles and k/P
ratios
Application of different Wall Functions e.g.
Analytical WF
Results from TEAM code for an upward heated pipe
flow
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Summary

• Different configurations of fuel pins in AGRs
  have been studied by CFD to calculate the
  pressure drop, fuel resistance and to optimise
  the design.
• Simplified geometries such as 2-d domains have
  been used to test the effects of varying k/P, Re
  and rib profiles, etc.
• Effective Sand Grain method was also used to
  estimate the friction factor and to compare it
  with the CFD results.
• For the Hoop design, 60o sector (3-d)
  configurations have been studied to give a better
  picture of the reactor core and to see how the
  arrangement of the fuel pins affect the flow.
• The simulation of more complex designs such as
  multi-start fuel pins are going to be tested on
  more powerful machines in the future.
• Different wall functions (mainly AWF) are
  currently being tested for mixed convection and
  are going to be used for ribbed surfaces.

Acknowledgements
This work was carried out as part of the Towards
a Sustainable Energy Economy (TSEC) programme
Keeping the Nuclear Option Open (KNOO) and as
such we are grateful to the UK Engineering and
Physical Sciences Research Council for funding
under grant EP/C549465/1.
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Supplementary Slides
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Wall Functions

• ? Standard Wall Functions
• Assume universal logarithmic velocity and
  temperature profiles in evaluating wall shear
  stress, turbulent kinetic energy production, and
  wall temperature.
• Inaccurate results when the flow departs from a
  state of local equilibrium.
• Different versions of these WFs are available in
  the STAR-CD, Code_Saturne, TEAM, and STREAM
  codes.
• ? Analytical Wall Functions
• Based on the analytical solution of the
  simplified Reynolds equations takes into account
  effects such as convection and pressure
  gradients, as well as the influence of buoyancy
  forces and changes in the thickness of the
  viscous sublayer.
• Have proved to be successful in many flow
  problems, e.g. buoyant flows.
• Currently available in the STREAM and TEAM codes.
• ? Numerical Wall Functions
• Based on an efficient one-dimensional numerical
  integration of the simplified LRN model equations
  across near-wall cells.
• Currently available in the STREAM and TEAM codes.