residuals

c120613 · December 19, 2009, 18:34

Dear all,

I'm doing the simulation of the flow around a stage of a Low Pressure Turbine and I want a suggestion.
I'm working with Ansys CFX, but I think my problem is not related to the software. I think I need to act on some numerical parameters.
I set residual limits for all of the equations as 1.e-06 and I'm using the k-eps.
The problem is that for momentum and mass residuals the values achieved are less than 1e-06, while for turbulence residuals the values achieved are not less than 1.e-06. Then the simulation continue as long as the maximum number of the iteration that I set at the begin of my simulation is achieved.

For this reason I have two questions:
- do you think the limit value of the residual: 1.e-06 is reasonable? is it too low?
- do you know which parameters do I have to change in order to achieve the converge for turbulence equations.

Kind regards

Domenico di Cugno

Abou ali · December 20, 2009, 02:51

Hi,
The residual level for turbulence transport equations (for k-eps, as well as the Reynolds stress components and the turbulent heat flux components) does not form part of the convergence criteria.
For detail on residual level see: Judging Convergence in ANSYS CFX-Solver Modeling Guide.

December 19, 2009, 18:34	residuals	#1
c120613 Member Domenico Join Date: Sep 2009 Location: Cranfield Posts: 48 Rep Power: 16	Dear all, I'm doing the simulation of the flow around a stage of a Low Pressure Turbine and I want a suggestion. I'm working with Ansys CFX, but I think my problem is not related to the software. I think I need to act on some numerical parameters. I set residual limits for all of the equations as 1.e-06 and I'm using the k-eps. The problem is that for momentum and mass residuals the values achieved are less than 1e-06, while for turbulence residuals the values achieved are not less than 1.e-06. Then the simulation continue as long as the maximum number of the iteration that I set at the begin of my simulation is achieved. For this reason I have two questions: - do you think the limit value of the residual: 1.e-06 is reasonable? is it too low? - do you know which parameters do I have to change in order to achieve the converge for turbulence equations. Kind regards Domenico di Cugno

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December 20, 2009, 02:51		#2
Abou ali Member Join Date: Nov 2009 Posts: 49 Rep Power: 16	Hi, The residual level for turbulence transport equations (for k-eps, as well as the Reynolds stress components and the turbulent heat flux components) does not form part of the convergence criteria. For detail on residual level see: Judging Convergence in ANSYS CFX-Solver Modeling Guide.