What does specific URF do to the simulation

omichalo121 · October 11, 2022, 04:37

Okay, i'm still working on a combustion furnace, so I can get the ideal temperature in thermocouples compared to the real ones. My supervisor recently changed temperature and energy URF from 1 to 0.5 and suddenly the temperature skyrocketed with very little change in fuel inlet.

Now the question, how does the temperature/energy URF influence the temperature in the furnace? From the plane view of Static Temperature it seems like there's little of energy coming out of the furnace, the whole volume is almost the same (in meaning of temperature contour).

Any help would be appreciated!

xisluke · October 13, 2022, 07:15

URFs shouldn't affect the solution (at least from a physical point of view). In few words, URFs aim at optimize the convergence process of your analysis by reducing oscillations within the iterative procedure. Basically, once the solution is solved, it is "blended" with the previous solution, in order to prevent from excessive variations in the result (explicit under relaxation). Another way is to apply relaxation directly within the matrix (implicit relaxation). Conceptually:

URF < 1 ---> Under-Relaxation
URF = 1 ---> No relaxation

The more you apply under-relaxation, the more your convergence will be slow and (theoretically) less prone to oscillation. Obviously, stability problems do not depend on URFs only. Usually the goal is to identify the best trade-off between stability and speed of the analysis.

October 11, 2022, 04:37	What does specific URF do to the simulation	#1
omichalo121 New Member Michał Basisty Join Date: Sep 2022 Posts: 4 Rep Power: 4	Okay, i'm still working on a combustion furnace, so I can get the ideal temperature in thermocouples compared to the real ones. My supervisor recently changed temperature and energy URF from 1 to 0.5 and suddenly the temperature skyrocketed with very little change in fuel inlet. Now the question, how does the temperature/energy URF influence the temperature in the furnace? From the plane view of Static Temperature it seems like there's little of energy coming out of the furnace, the whole volume is almost the same (in meaning of temperature contour). Any help would be appreciated!

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October 13, 2022, 07:15		#2
xisluke Member Luca Join Date: Mar 2021 Location: Italy Posts: 56 Rep Power: 5	URFs shouldn't affect the solution (at least from a physical point of view). In few words, URFs aim at optimize the convergence process of your analysis by reducing oscillations within the iterative procedure. Basically, once the solution is solved, it is "blended" with the previous solution, in order to prevent from excessive variations in the result (explicit under relaxation). Another way is to apply relaxation directly within the matrix (implicit relaxation). Conceptually: URF < 1 ---> Under-Relaxation URF = 1 ---> No relaxation The more you apply under-relaxation, the more your convergence will be slow and (theoretically) less prone to oscillation. Obviously, stability problems do not depend on URFs only. Usually the goal is to identify the best trade-off between stability and speed of the analysis.