[aestas]

Hi friends,

I am working on a arc welding problem using VOF model.

I need to convert some surface force (pressure and surface tension) to volume force on the interface and add them on the momentum equations.
In Fluent help, the volume force of surface tension that is added to the momentum equation has been given using the divergence theorem:
1.jpg

But, i do not understand why.

If i want to convert pressure to the volume force using the similar method, how to do it?

[kirmaks]

Hallo,

it may be very tricky. As far as I remember from the theory, the force due to the shear is Stress*Area. You can use very thin elements aligned with the boundary and apply this force (divided with density) to the cell centres only in the first layer of the near boundary cells, but it will work if Your boundary is already known and meshed accordingly.

You never have well defined boundary with VOF, so You need to identify the boundary (phase 1 = 0.5), somehow find the cells with the melted material on this boundary and their boundary neighbours, somehow get the tangential stresses on the cells (from Lorentz force or Marangoni stress) and apply them as volumetric sources.

I'm afraid You will not get the working code for such complicated problem here.

Good Luck and regards, Maks.

[aestas]

Thanks for your reply,Maks.

I am trying to use the similar method to convert other surface forces into volumetric surface force by the following equation:
1jpg.jpg

the surface forces multiplied by the gradient of VOF.(the detailed explanation was in Brackbill et al. (1992), which is also referenced by Fluent, but i have not fully understand . )

As to the free boundary, i have successfully identified it by using both the value of VOF((as you said, phase 1 >= a certain value larger than 0)) and the gradient of VOF (at the boundary the absolute value of gradient of VOF must be greater than a certain value.).By using these two conditions, the very first layer on the free boundary could be identified.

Originally Posted by kirmaks

Hallo,

it may be very tricky. As far as I remember from the theory, the force due to the shear is Stress*Area. You can use very thin elements aligned with the boundary and apply this force (divided with density) to the cell centres only in the first layer of the near boundary cells, but it will work if Your boundary is already known and meshed accordingly.

You never have well defined boundary with VOF, so You need to identify the boundary (phase 1 = 0.5), somehow find the cells with the melted material on this boundary and their boundary neighbours, somehow get the tangential stresses on the cells (from Lorentz force or Marangoni stress) and apply them as volumetric sources.

I'm afraid You will not get the working code for such complicated problem here.

Good Luck and regards, Maks.

[anoop.k.unni]

Originally Posted by aestas

Thanks for your reply,Maks.

I am trying to use the similar method to convert other surface forces into volumetric surface force by the following equation:
Attachment 52153

the surface forces multiplied by the gradient of VOF.(the detailed explanation was in Brackbill et al. (1992), which is also referenced by Fluent, but i have not fully understand . )

As to the free boundary, i have successfully identified it by using both the value of VOF((as you said, phase 1 >= a certain value larger than 0)) and the gradient of VOF (at the boundary the absolute value of gradient of VOF must be greater than a certain value.).By using these two conditions, the very first layer on the free boundary could be identified.

Hello,
Did you find a solution for the mentioned problem. I want to know how to convert the surface to volume source term. if you know,please share

[Venky_94]

Originally Posted by anoop.k.unni

Hello,
Did you find a solution for the mentioned problem. I want to know how to convert the surface to volume source term. if you know,please share

Hey I'm facing the similar issue as well. I've written a UDF for the source term but I'm facing issues with handling the scalars and vectors together. Did you figure out a solution?