## Fluids

#### Periodic conditions in two dimensions

• Amir
Subscriber

Hello everyone,

I am going to study a 2d two phase problem in a periodic domain, from left to right periodic also bottom to up

so defined two pairs of peridoc boundary conditions,

there is no pressure gradient, between two sets of periodic boundaries (in x and y direction).

in the tab of periodic conditions, there is only one pressure gradient option (which I set to 0), also one flow direction (I set x =1 and y=0, but my case is in two directions periodic and should let the droplet flows in two directions)

My question is how I should do the right setup for my case? as it seems my droplet only flows in x-direction.

• Prashanth
Ansys Employee

Hi

I think adding few screenshots of the model you are currently working on might be helpful to undertand the problem better.

• Amir
Subscriber

Hello, thank you for the reply. This image is for one case, for every other cases, I also need x direction and y direction periodic BCs.

• Prashanth
Ansys Employee

Hi

If you are trying to track multiple parallel patched bubbles, reconsider what you are trying to do here. Switch to a 3D domain section to actually study a bubble travel with two extreme sides reserved for inlet and outlet. Set the rest of the planes as periodic or symmetry.

• Amir
Subscriber

thank you, in fact I am trying to study coalescence of some small droplets, this image above would be the final shape,

here in this problem should not be any inlet and outlet, so the desired BCs are periodic which in the simulations using coding and methods like lattice boltzman method are common, i.e., two pair of periodic BCs.

is there any way to use two pairs of periodic BCs horizontally and vertically without any pressure gradient horzontally and vertically so the droplet able to freely move in two directions of the so-called periodic domain?

• Rob
Ansys Employee

You can only have one paired set of translational periodic boundaries.

• Amir
Subscriber

OK, thank you, so that is the software limitation,

Is it possible to write a UDF for this purpose as an equivalence?

• Rob
Ansys Employee

It's possible, but I'll leave you to write it. Please post the code once you've got it working so others can benefit.

• Amir
Subscriber

Ok thank you