Learning Forum

[nobrien]

Hello!

I am conceptualizing a way to pair the discrete phase model with acoustic simulations to model things like acoustic levitation. The particles are very small, around 10 micron, so discrete phase model would be the best option for me for the particle-side.

It seems most prior works have used ansys mechanical to do a first-order approximation of the pressure/velocity waves, but I also have a flowing fluid in my model, which would cause drag forces on the particles, too. Is there a way to compute the flow induced by pressure waves in a fluent simulation and use that solution to compute the forces on particles?

I know it is possible to do do a fully transient wave-propagation simulation, but I am assuming the time-step would need to be terribly small to account for the speed of the sound wave (around 300 m/s). Does anyone have any input? I am also very new to acoustics and wave-propagation.

Thanks!

[Rob]

You'd need to resolve the pressure pulses so you'd need a very fine mesh and tiny time step as you suggested. 

There are force report macros for DPM particles via a UDF. There are also DPM scalars. Do you need to model the pulses or can you use any of the acoustics options from Fluent and map that value onto the particle? 

Note, as this isn't part of the core code I'm very limited in what advice I can give. DPM scalars are covered in the UDF manual, and the Fluent acoustics is in the User's Guide. You may also find material in the Fluent Help system (tutorials and examples) and in Learning (Fluids - left menu here). 

[nobrien]

Thanks for the response, Rob. I spent some time looking into the code and the physics, so I think the approach I'll take is this:

1. Calculate pressure-velocity waves in ANSYS Mechanical.
2. Use those fields to calculate a force-field in the domain.
3. Export to Fluent and hold in memory as User-defined memory
4. Write a UDF in Fluent to use that force field in addition to drag and gravity forces.

The Fluent Acoustics seem like they may be a bit overkill for what I need and what I've seen other analysts do in literature. 

My next problem is using ANSYS Mechanical for the acoustics simulation and exporting the results to load into Fluent. Would you have any tips on doing that? Could I simply import the results file from a Harmonic Response analysis into Fluent and have access to the result fields from ANSYS Mechanical? I assume I'll actually need to export as some other format and write a UDF to read those results into memory...

[Rob]

You may want to explore interpolation files for Fluent combined with User Defined Memory. That may be an easier way of getting the results out of Mechanical. The UDF then uses the UDM plus whatever else you want/need from the data.