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Update on CAST CFD Simulations
Ideas for coherence length parameterizationand
Tuning Windows Temperatures
06.08.2013 – Cenk Yildiz
Part 1:Coherence Length
Parametrization
Problem1: Short length for tilted sims• Tilted Simulations can have very short length
due to hydrostatic pressure difference
Problem1: Short length for tilted sims• One should be able to use the rest of the profile
(with different photon mass)
Solution• Remove effect of hydrostatic pressure from the profile(remove the tilt)• Calculate coherence
length for DST=1E-3• Use the coherence
length, P_CB and Peng-Robinson equation(or Refprop) to calculate the density at any point inside this length.
• Calculate conversion probability integrating through the whole length. (effective photon mass will be a function of length)
• The cost will be computing time.
Problem 2: How to find length for any angle• How can we parametrize the length for
(pressure, angle)?• How can we chose model for intermediate
angles:– The horizontal simulations use laminar model on
both MFB,MRB– Tilted simulations use half Laminar model
(MFB:laminar, MRB:turbulent)
• Comparing different models:Problem 2: How to find length for any angle
Big difference in laminar side
Tiny difference in turbulent side
Very big difference from tilted to horizontal simulation
• Comparing different models:Problem 2: How to find length for any angle
Note that for angles < 1deg, half Laminar simulations
doesn’t converge! (under investigation)
Solution
• Simulating -6,-3,-1,0 degree for all pressures, and do a 2 dimensional fit for pressure – angle?
Part 2:Tuning Windows
Temperatures
Reminder…
• Laminar horizontal, and Half Laminar tilted simulations gives the closest pressure difference when tilting, thus is the model we chose for cold windows.
• Windows Temperature values and change in windows temperature while tilting is worse.
Reminder: Comparison of Pressure Change
Reminder: Comparison of Change in TMFB
Reminder: Comparison of Change in TMRB
Update: Changing CW Boundary Condition
Set to 130K
instead of 90K With this change, simulated temperatures are closer to experimental temperatures
Comparison of Temperatures(only laminar/half Laminar models)
T-MFB
T-MRB
Horizontal(Laminar) Tilted(Half Laminar)
Comparison of Change in TMFB
BC=130K
Comparison of Change in TMRB
BC=130K
Pressures and Coherence Length
• Pressure change is within 0.03mbar of old boundary condition(Only for 98 mbar change in pressure is 0.13mbar higher)
• Gas is pushed more to inside, the coherence length is smaller– Around 0.5m for horizontal cases(laminar)– Around 0.2m for tilted cases(half laminar)
Conclusion
• Coherence length:– We need to use a new method to be able to use
the whole length in the tilted cases.• With new Temperature boundary condition:– Temperatures are closer to experimental values.– Temperature change during tilting is worse.– Coherence length differs in order of 0.1-0.5m– We can always fine tune temperatures to reach
the experimental data, but is there a point?