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300 m/s Convergence Issues

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Old   April 12, 2019, 13:24
Post 300 m/s Convergence Issues
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Jack Wilson
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I am currently working on modelling compressible flow around a Golf Ball with the velocity set at 300 m/s, however I am having trouble getting it to converge.

In terms of meshing I have an inflation mesh around the Golf Ball and a face meshing set on the Golf Ball. As well as a body of influence covering the area behind the Golf Ball. With this mesh my Y+ Value is between 0 and 3

The setup within Fluent is as follows:

- Density Based
- Air - Density: Ideal Gas - Viscosity: Sutherland
- K - Omega - SST
- Solution Method - Explicit with all set to First order methods
- Solution Controls:
- Courant Number: 0.5
- Residual Smoothing Operations: 20
- Multigrid Levels 2
- Relaxation factors are all a third of original values

Using these settings and trying several other methods I am not able to reach a state of convergence and my residuals are only as good as shown in the attached image.

I have only been using Ansys Fluent for a couple of months so any help would be greatly appreciated.
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Old   April 15, 2019, 13:37
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Lucky Tran
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It looks typical. You just want lower residuals or what?


Make some plots of velocity and see if it looks good or if completely whack. If it looks good, keep cranking. If it's whack, probably a mesh issue.
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Old   April 15, 2019, 14:01
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Melih MeriÁ
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did you try different turbulence model? and did you try enchancement wall treatment option.. flow structure on the ball is highly complex and you have flow separation and secondary flows.. and you have to choice correct flow volume and mesh quality metrics..
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Old   April 16, 2019, 14:56
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Pramod Narayan
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This type of problem is highly dependent on mesh quality. Check for mesh metrics like skewness and orthogonal quality. If possible, try to have as many Hexahedral elements as possible in your mesh ruining the quality.

You could also start your simulation in transient and run the simulation for a few hundred time steps before switching over to steady state.
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compressible flow problem, convergence, help for a newbie

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