## General

#### Why don’t the residuals converge in my conjugate heat transfer problem in Fluent and is there any way I can converge the solution?

• FAQ
Participant

Occasionally it may be difficult to converge the energy equation in Fluent for a conjugate heat transfer problem. The most common causes of the problem and their resolutions are summarized here. Causes: ========= 1. Poor mesh quality: high size change, and/or high skewness, and/or coarse mesh 2. High jump in thermal conductivity 3. Invalid boundary conditions 4. Improper mesh scaling Resolutions: ========= 1. Make sure mesh is scaled properly. Go to Mesh â€“> Scale 2. Double-check model setup and boundary conditions 3. Reduce explict-relaxation, using the following 3 lines: (rpsetvar â€˜temperature/explicit-relax? #f) (rpsetvar â€˜explicit-relaxation? #t) (rpsetvar â€˜temperature/explicit-relax 0.1) By default, explicit-relax is set to 1.0. 4. Keep implicit underrelaxation to 1.0, by using the following line: (rpsetvar â€˜temperature/relax 1) 5. Use alternative wall formulation, which can be activated using the following TUI command: /solve set expert , yes , , , 6. Ignore secondary gradients on all the cells, but shell conduction walls (if you have them), by using the following rpvar: (rpsetvar â€˜temperature/secondary-gradient? #f) By default, this is #t (true). To obtain the value, type: rpgetvar â€˜temperature/secondary-gradient?) which will return either #t or #f. Warning: This may bring some measureable inaccuracy, depending on how skewed the cells are at the wall and how high is the magnitude of the wall heat flux. 7. If you have turned on shell conduction in any of the walls, ignore secondary gradient in shell conduction zones only using the following command: (rpsetvar â€˜temperature/shell-secondary-gradient? #f) This does not cause measurable inaccuracy.