Hi, I simulate a wind turbine using Ansys fluent (3D simulation). My objectives are to study the rotor aerodynamic performances and to visualise the fluid flow around it. In the calculation step, the continuity residual couldn’t reach a value below than 10^_3.
How can I solve this problem? And what is the acceptable value of the continuity residual?
Hello,
Why do you think you need to lower the continuity residual further?
1e-3 is generally the 'upper permissible' value for the continuity residual, however convergence criteria are not only based on residuals.
You should monitor a parameter of interest/relevant to your set up/what you want to compute (pressure drop, mass flow, etc...).Your solution can be deemed converged only if the monitor curve goes "flat".
In most cases, it is impossible to reach 10^-4 or less with the continuity. Again, the best way to check the convergence is monitoring the convergence of some variable (such as velocity, temperature, pressure, force, and so on ) in a desired point, surface, etc. By monitoring this value and the residuals as well, you can make sure that the problem is converged.
Hi Somaya Younoussi,
Please explain more about the project and the fluent settings.
Is your mesh good enough? Report the mesh quality, specially skewness.
Transient or steady-state?
Which turbulence model do you use? Do you keep y+ in the acceptable range?
Which pressure-velocity coupling scheme do you use?
Have you changed the under relaxation factors?
As Kira Haller said, you should monitor some parameters and check their value to check the convergence.
Kira Haller, thank you for your answer. I monitor the convergence of axial force and moment. I found in some web sites that the residuals values must be 10-5 or 10-6 to achieve problem convergence.
Somaya Younoussi , so this 10^-5 to 10^-6 convergence refers to the RMS residual, not the continuity residual.
Ashkan Ghafari, I answer your questions bellow:
- Orthogonality: 0.75113, and skewness: 0.22213.
- Steady simulation.
- SST Transition turbulence model. The y+ value is about 1.
- SIMPLE.
- Yes, I changed them in order to achieve 10-5 of continuity residual.(pressure: 0.2, Momentum: 0.5, turbulent kinetic energy:0.5, dissipation rate: 0.5).
Somaya Younoussi Fluent uses a finite volume discretisation. For each finite volume a "control volume" or finite volume equation is assembled in the form:
App*PHI + SUM(Anb*PHInb) = Residual
The RMS (Root Mean Square) value is simply the RMS average of all the residuals on the right hand side of your equations.
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