Learning Forum

[CHan Cheung]

Dear LS-DYNA Community, I am currently developing a 3D model using the DEM coupled with ICFD functionality in LS-DYNA. In my model, DEM particles are bonded into a large rectangular structure, resembling a train, approximately 100 meters in length. This is achieved through the De_bond command. ICFD is utilized to simulate the natural air surrounding this structure. For the air domain, which extends several kilometers and is rectangular, I've set 'free slip' boundary conditions on all six sides. The primary focus is on modeling the high-speed airflow that results from the structure's movement through the surrounding air. Having previously worked with EDEM coupled with FLUENT, I was accustomed to detailed air pressure data outputs, including dynamic, absolute, relative, static, and total pressure, all reported separately. However, in the ICFD results post-processing in LS-DYNA, it appears that only fluid pressure is available, lacking the detailed division found in FLUENT's results.

My questions are as follows:

Can LS-DYNA's ICFD post-processing differentiate and display various types of air pressures such as dynamic, absolute, relative, static, and total pressure?

Does ICFD in LS-DYNA account for atmospheric pressure in its simulations? If my goal is to simulate a natural air domain, is setting 'free slip' as the boundary condition on all six sides of the air domain the optimal choice?

Are there specific boundary conditions within LS-DYNA that can incorporate atmospheric pressure, or should I maintain the boundary pressure at a constant zero (as observed in some official website examples)? 

Your insights and recommendations on these aspects of ICFD modeling in LS-DYNA would be invaluable to me. Thank you for your guidance and support.

[Ashish Khemka]

Hi,

Please see if the examples here help: ICFD — Welcome to LS-DYNA Examples

Advanced examples — Welcome to LS-DYNA Examples

Regards,

Ashish Khemka

[Reno Genest]

Hello Chan,

There is only one pressure result in ICFD; this pressure is the pressure variation from the reference pressure. There is the following information in the iCFD training:

"Operating pressure versus absolute pressure
•
In many cases, the range of pressure variations under which a system works (operating
pressure) is a lot lower than the atmospheric (absolute pressure) pressure (a few hPa for P atm =
1000 hPa
•
For numerical stability and precision, it is often advised in CFD solvers to set up the reference
operating pressure at 0.
•
The results for pressure will therefore represent the pressure variations from the absolute
reference pressure (usually atmospheric pressure). Consequently, negative values for pressure
can be found.
•
Warning : this method is only valid in incompressible solvers where no EOS needs to be
defined!"

 

So, setting the pressure=0 at a boundary is a way to set the atmospheric pressure.

Also, the *ICFD_BOUNDARY_FREESLIP keyword means the velocity in the normal direction is zero. This can be used as a symmetry condition.

 

Refer to the ICFD examples to see how different problems are solved with the ICFD solver.

 

Reno.