Learning Forum

[Dennis Chen]

Hello, if possible, I like to confirm some basic understanding of ICFD turbulence models.     To that end, I have a few questions, maybe basic but really appreciate your help:

1) if I don't use ICFD_control_turbulence or ICFD_Boundary_prescribe_turbulence in a ICFD model in LS-Dyna, does the solver still utilize some default turbulence model or is turbulence (say vortex shedding) completely turned off?  

2) I have a simple air flow though channel against a ball (spherical wall) problem and if I turn on ICFD_control_turbulence or ICFD_Boundary_Prescribe_turbulence, the solution simply hangs.   I tried different boundary layers thickness/growth in mesh_BL and looked at K-E and K-omega models and tried different inlet velocity conditions, but the solution simply hangs (seems to indicate divergence) and velocity reading is completely wrong. 

In fluent, this would have terminated the job but in Dyna, it seems to be going forever without terminating.    is it possible to help me understand the general logic of what the ICFD solver is checking when we turn on turbulence models?  

I also appreciate any reading material on this topic.   I've been looking at the basic problems and try to look at the fluent tutorials to try to redo them inside Dyna.   My ultimate goal is to utilize LS-Dyna for strongly coupled FSI problems where even the simplest types of problems become impossible in system coupling between Fluent and Mechanical and that's why Dyna becomes very advantageous. 

Thank you for your help. 

[igandiko]

Hello,

1. Turbulence is turned off if *ICFD_control_turbulence card is commented out. 

2. Could you please try the latest dev build? Does the simulation hang or is it slow? Perhaps the velocity field solving step needs more iteration steps. There are multiple improvements in dev version on the convergence for solving velocity field and the turbulent wall model. You can also try adding *ICFD_SOLVER_TOL_MMOV with a value for MAXIT to limit the number of iteration.

Regarding the training materials, you may have to check Ansys learning hub and dynalook.com. 

[Dennis Chen]

Hi igandiko, thank you.    I am mostly exploring this at home using student license.   I may stay in 2D from now on. 

There's not a lot of official training material out there but there's enough on dyna example and documentation to set up and learn from simple examples.    

I think Dyna's advantage here is just for simple FSI problems which would have taken a long time in system coupling so I am trying to explore and learn to that end.