Achimedes Buoyancy force bug

Submitted by rqwang on Thu, 08/18/2011 - 21:09

Hi cfdemers,

I found the magnitude of Achimedes Buoyancy force is low by the 4th order.

Please check the magnitude of this force.

BTW, I suggest use Achimedes buoyancy force instead of lift force. The latter is often referred to the normal force to ambient flow induced in shear flow.

Thanks.

rqwang

Forums:

cgoniva's picture

cgoniva | Fri, 08/19/2011 - 08:54

Hi rqwang!

The code sais:
force = -g_.value()*rho_[cellI]*pow(dp,3)/6*M_PI;
which does not seem to be too wrong.

Could you please provide a case where you experienced strange results?

Cheers,
Chris

rqwang | Fri, 08/19/2011 - 15:17

Hi Chris,

I printed out the density. It's just 1.

How should I simulate particles in water?

Could you setup a place to enter the value of rho?

I tested how much force is applied and the acceleration of the particles. It looks correct.

Thanks.

rq

cgoniva's picture

cgoniva | Sun, 08/21/2011 - 22:18

Hi rq,

now we are getting closer ...
the force model is looking for a fluid density field "rho".
you can specify the name of the field which is used as "rho" in in the couplingProperties/ArchimedesProps sub-dict.

so, if the solver you use does not have its own density field, there is the need to provide a "dummy" density field, as done in cfdemSolverPiso.

Just manipulate the field in case/CFD/0/rho to the desired value.

Cheers,
Chris