{"id":164975,"date":"2023-03-17T08:59:08","date_gmt":"2023-03-17T08:59:08","guid":{"rendered":"\/knowledge\/forums\/topic\/what-are-some-of-the-best-practices-recommendations-for-a-converged-solution-in-transient-flow\/"},"modified":"2023-07-31T12:26:39","modified_gmt":"2023-07-31T12:26:39","slug":"what-are-some-of-the-best-practices-recommendations-for-a-converged-solution-in-transient-flow","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/knowledge\/forums\/topic\/what-are-some-of-the-best-practices-recommendations-for-a-converged-solution-in-transient-flow\/","title":{"rendered":"What are some of the best practices \/ recommendations for a converged solution in transient flow?"},"content":{"rendered":"

1. Start with converged steady-state solution when applicable (when the initial transient solution is not important). 2. You could use either SIMPLEC (will be fastest if holds together) or coupled solver. Alternatively, depending on the simulation, you could start with SIMPLEC and then switch to the coupled solver. 3. All Under Relaxation Factors are to be kept at 1 ( or close to 1 provided stability is achieved). 4. Courant = infinity (1e+06) in pressure based coupled solver (which is no relaxation). 5. dt is chosen such as to maintain convective CFL =1 (this value can be reported under velocity) and acoustic CFL =1 (if solving for acoustics). 6. No more than 10 iterations \/ time step. More than that are not needed if CFL ~1. 7. You could “ignore” the residuals as long as they drop per time step. Dropping of residuals to 3 orders of magnitude is not absolutely necessary, especially continuity. 8. In transient solution, residuals do not represent converged solution. Flow variables are not converged during sub iterations, what is updated during sub iterative cycle is flux values which come from the previous step and then are updated using the flow variables at the current step. However, to monitor convergence, you could use the variable of interest and monitor the variation as the simulation progresses.<\/p>\n","protected":false},"template":"","class_list":["post-164975","topic","type-topic","status-publish","hentry","topic-tag-2020-r2","topic-tag-fluent","topic-tag-fluid-dynamics","topic-tag-general","topic-tag-general-fluent"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t