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Temperature variations with increasing number of iterations

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Old   December 15, 2012, 02:00
Question Temperature variations with increasing number of iterations
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Arpit Raj
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Hi everyone,

Hope you are doing good.

I am actually simulating a program in FLUENT with the following settings:

Boundary Conditions
Turbulent Intensity: 4.5
Hydraulic Diameter: 25.3371
293K [water] 300K [vapour]

Sizing 2mm
Mapped Free Meshing

Boiling Model
RPI Boiling Model
Viscous Model k-epsilon
Enhanced Wall Treatment
Thermal Effects
Per Phase

Diameter: sauter-mean,
Drag Coefficient: boiling-ishii
Lift: boiling-moraga
Heat: ranz-marshall
Mass: boiling
Surface Tension: 0.06
Interfacial Area: ia-particle

Solution Controls
Flow Courant Number: 10
Body Forces:1
Vaporisation Mass:1
Volume Fraction:0.5
Turbulent Kinetic Energy:0.8
Turbulent Dissipation Rate: 0.8
Turbulent Viscosity:1

When I run the simulation for around 300 iterations, the residuals become flat and there are no fluctuations. The output obtained is as desired (temperature, pressure, velocity of water, velocity of vapour). But when I increase the number of iterations, say like, to 1000 then the temperature profile changes drastically keeping the remaining (pressure, velocity of water, velocity of vapour) same as before.

Could anyone please help me in knowing what I am doing wrong???
Thanks a lot in advance.
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Old   December 15, 2012, 18:16
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Have you reached convergence (i.e. have your residuals gone below the convergence criteria)?
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Old   December 16, 2012, 04:23
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Arpit Raj
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Thanks Meangreen for the prompt reply!!!

Earlier I had set my residuals criteria to 1e-6 then it was not converging as most of the parameters became flat after 1e-4. So, when I set my residual criteria to 1e-3 then it converged. I am attaching the snapshots of the plot when I had set number of iterations to 1000.
Attached Images
File Type: jpg Residuals.jpg (21.6 KB, 11 views)
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iterations increase, multiphase

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