Why Am I Getting Temperature Divergence In Amg Solver 3m1451

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Asked 3 years ago

Raman S Chary Czech Technical University in Prague

Why am I getting temperature divergence in AMG solver? Hello, The case is with regards to a 2-D Axis-symmetric pipe - turbulent flow - water - density varying with temperature - polynomial ( 6th order ) I have reduced the under relaxation factors for all of them to very low but am still getting the same error. Thanks a lot.. !!!

ThermoFluids Modeling using CFD

FLUENT

Polynomials

CFD Coding

Turbulent Flow

CFD Simulation

Computational Fluid Dynamics

ANSYS

AMG

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All Answers (18)

John Kaiser S. Calautit University of Nottingham

3 years ago

Try the following: - Refine your mesh - Check boundary conditions - If available, use Hybrid initialisation

Soheil Akbari Iran University of Science and Technology

3 years ago

choose the variation of water properties according to operating conditions and use multiphase model (mixture model). fixed the temperature of vapor phase in cell zone condition.

Raman S Chary Czech Technical University in Prague the mesh is already refined... and after using Hybrid Initialization

3 years ago

Divergence in AMG solver : "k"

Ashish Saxena Nanyang Technological University

3 years ago

Try with using second order solvers. Let us know how you will be able to solve the same, if you will.

Raman S Chary Czech Technical University in Prague

3 years ago

I used 2nd order solvers as default... even before the error came. !! I then changed the Dentsity equation to 2nd order... then it solves faultlessly.. !! But not with the 6th order I first tried... !! Thanks a lot everyone for your contributions.. !

Mahesh K. Varpe Ramaiah University of Applied Sciences

3 years ago

Check mesh quality for skewness (0.5 is adequate). Check the model if its is properly scaled or for  units.  First switch off energy equation and density variation. If simulation runs smooth then enable energy equation. After this if it is OK, specify density variation ( first try simple relation and then custom desired). 2 Recommendations

Rajesh Alayil Indian Institute of Technology Madras

3 years ago

Hi Raman, along which axis are you applying axis-symmetry.  usually this error appears when you have any problem with mesh, boundary conditions, models etc. But for axis symmetry problems, it can be due to the axis also. the axis-symmetry condition should be always along the x direction. Please check this out and try it. Regards, Rajesh 2 Recommendations

Raman S Chary Czech Technical University in Prague

3 years ago

Yes... I checked with the axis-symmetric conditions and it was along the x-direction. As Mahesh said I also tried switching off the density variation and energy equation at the beginning. The simulation was very smooth without them. With energy its okay but the the problem starts with the density polynomial.

I was forced to use a polynomial of lower order the problem got solved. Thanks everyone... !!! Raman

Jigar Soni Gujarat Technological University

3 years ago

sir i am also facing the same problem of divergence but i don't know how to check the axis symmetry...please guide

Rajesh Alayil Indian Institute of Technology Madras

3 years ago

@Jigar, check where you have applied axis symmetry condition in the solution domain. Is it along the x or y axis. Regards, Rajesh. 1 Recommendation

Rajesh Alayil Indian Institute of Technology Madras

3 years ago

@Raman, how about the quality of your mesh. What initialization scheme are you using ? Regards, Rajesh.

Raman S Chary Czech Technical University in Prague

3 years ago

Im using Standard initialization calculated which has been to all zones. !! I think the problem is with the 6th order equation of pure water's density dependance on temperature. Its provided by UNESCO so I thought of going ahead with it. .!! Its equation number : 8.4 on the second page.. !!! Is this equation legitimate. ? ocen689ch8.pdf · 178.69 KB

Steffen Hain-Würtenberger Magna Powertrain Bad Homburg GmbH Hello Raman,

3 years ago

Often when I had problems with temperature divergence, it could be managed by setting a lower temperature limit. Default value in many CFD packages is 6000 K or so. If you allow the solver for such unreasonable numerical excursions (in common engineering problems), it may happen that you are already lost right at the beginning and numerical stability is gone and can't by recovered by any mean. This is not necessarily a question of mesh quality. Just try it. Regards, Steffen

Ashish Saxena Nanyang Technological University

3 years ago

Have you tried using second order upwind solver scheme??

Raman S Chary Czech Technical University in Prague

3 years ago

Yes Im using Second Order Upwind solver... and I changed the limits according to Steffen... The problem persists because of the 6th order density equation of water.. !! The problem solves flawlessly when changed to a simple 2nd order equation. 1 Recommendation

Leandro Campos ArcelorMittal

7 months ago

Hey Raman, did you solve your problem? Would you mind to share with us? I'm having the same here... Thanks!

Raman S Chary Czech Technical University in Prague

7 months ago

Hey Leandro, The problem was that I was trying to use the 6th order polynomial for the relation of density of pure water with respect to change in temperature. It was way too much for fluent :D I used a 2nd order polynomial and the simulation worked effortlessly. 1 Recommendation

Pei Sun University of Sussex Hi Raman, Thank you so much!

3 months ago

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