Question

Hello! I have a question related to Ansys Fluent. I am studying on the air flow 2-D. I used the triangular mesh and refinement. I am a beginner of the Ansys Fluent, so I used to see some video on Youtube, they said that after running calculation and if it appears "the solution is converged", it means we get the perfect result, so we do not need to increase number of iteration anymore, we should stop by this point. However, for my case, I have increased the number of the iteration from 10 to 6000, but it still didn't show the sentence "the solution is converged", thus should I keep going on increasing the number of iteration? But is it not too many iterations (6000), now? Thank You in advance! I will thumb you up!

x B:Air flow 2D Triangular mesh Fluent@Sunrise [2d, dp, dbns imp] [ANSYS CFD] File Mesh Define Solve Adapt Surface Display Report Parallel View Help @' in ZA PEMOS 1: Scaled Residuals Run Calculation Check Case... Preview Mesh Motion... Residuals continuity -X-velocity y-velocity energy 1e+01 ANSYS R15.0 Reporting Interval Number of Iterations 6000 Profile Update Interval 1 1e+00 Meshing Mesh Generation Solution Setup General Models Materials Phases Cell Zone Conditions Boundary Conditions Mesh Interfaces Dynamic Mesh Reference Values Solution Solution Methods Solution Controls Monitors Solution Initialization Calculation Activities Run Calculation Results Graphics and Animations Plots Reports Solution Steering Data File Quantities... Acoustic Signals... Calculate 1e-01 0 1000 2000 4000 5000 6000 3000 Iterations Help Scaled Residuals Jul 01, 2020 ANSYS Fluent 15.0 (2d, dp, dons imp) 5996 5.4834e+90 5.5516e+99 3.6297e+90 5.4989e+90 6:00:00 4 reversed flow in 2 faces on pressure-outlet 8. 5.5999e+90 5.5555e+90 3.6291e+90 5.5184e+99 9:30:91 3 reversed flow in 2 faces on pressure-outlet 8. 5998 5.5156e+90 5.5661e+30 3.6313e+36 5.5344e+G6 6:00:00 2 reversed flow in 2 faces on pressure-outlet 8. 59995.5225e+90 5.5658e+30 3.6329e+36 5.542 Ge+96 6:00:00 1 reversed flow in 2 faces on pressure-outlet 8. 6909 5.5268e+30 5.5712e+99 3.6351e+30 3.6351e+36 5.5465e+30 6:00:00 6

Answer 1

The error you are facing is reversed flow in 2 faces on pressure-outlet 8. It occurs when pressure gradients due to geometry mean that the flow wants to re-enter the domain at the location where you have placed an outlet. This effects the mass-conservation and thus convergence. Some of it can be tolerated but still, it is highly recommended to minimized or eliminated this. Things you can try to minimize/eliminate this:

1. A better distribution of mesh sizes and elements leading up to the outlet.

2. Moving the outlet position further downstream

And Yes, you can increase your iterations as well.

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