Absence of Angular Momentum

Submitted by abhishek_basak on Tue, 08/23/2011 - 10:08

Hello,

It seems (from your email) that angular momentum for the solid spheres are not taken into account. I think this is a problem, in absence of angular momentum will change the dynamics of the particle.

Consider a ball moving upwards in a a cross flow (i.e. ball moving upwards in +ve y direction, flow in +ve x direction), then deflection of ball from the straight path would be different if angular momentum is considered.

Any comments,
Abhishek

Forums:

cgoniva's picture

cgoniva | Tue, 08/23/2011 - 13:08

Hi Abhishek,

I do agree with you, but only for cases where:
+ particles rotation velocity is very high (Magnus force),
+ gradients in the flow field are significant compared to particle size (Saffman lift force),
+ viscosity is rather high otherwise above forces might be negligible.

In other words, for glass particles in air angular momentum can be neglected as a first guess, for plastic balls in oil they should be considered.

In principle, the CFDEM framework is perfectly fine suited to include above mentioned forces besides drag, buoyancy and virtual mass force which are currently in the CFDEM release.

Cheers,
Chris

rqwang | Tue, 09/20/2011 - 04:43

Hi Chris,

I noticed the variable omega in CFD-DEM.

Does it represent the particle rotation?

Thanks.

rq

cgoniva's picture

cgoniva | Tue, 09/20/2011 - 16:49

Hi!

Yes, omega represents particle rotation.
Currently it is not used in particle-fluid interaction.

Cheers,
Chris

rqwang | Tue, 09/20/2011 - 17:25

Hi Chris,

So omega is not accurate in the current version, is it?

I am trying to setup a magnus force. Is it ok to use omega?

Thanks.

rq

ckloss's picture

ckloss | Thu, 10/13/2011 - 17:33

Currently not, you would have to
+ add a fix couple/cfd/torque on the LIGGGHTS side (very much alike the fix couple/cfd/force)
+ add a CFDEM submodel to add a torque
+ change the cloud class in CFDEM so that particle omega is pulled from LIGGGHTS and particle torque is being pushed to LIGGGHTS

Christoph

rqwang | Fri, 10/14/2011 - 02:56

Hi Christoph,

Thank you for your suggestion.

I am not familiar with LIGGGHTS and it looks much work to do.

I am simulating a particle-laden jet in still water with LES. It seems angular momentum is essential for the simulation.

May I know whether you have a plan to couple the angular momentum in the near future?

Thanks.

rq

cgoniva's picture

cgoniva | Thu, 10/27/2011 - 17:09

Hi rq,

it is not on our "nearest-future schedule" as we currently cannot raise a funding for that topic.

In case you can come up with some literature on that and ideas how to implement it, it would be highly appreciated!

Cheers,
Chris