SimScale CAE Forum

CFD Flow for CHW Header and Piping System

I am creating a velocity/pressure analysis for a piping system. I am wondering if how the simulation takes elevation change into affect and which direction the program assumes for gravity. I would assume gravity in the negative Y direction but I want to make sure that is correct. Also I am wondering why there is an option for initial conditions when it seems the boundary conditions override this in the end anyways.

Thanks in Advance for your Help!

Tyler Graves
TAMU Engineering Student '20

Hi @tgraves!

The only modules having gravity implemented are convective heat transfer & multiphase flow as far as I can tell. The incompressible solver does not have such an option (@1318980 & @dzivkovic, correct me if I am wrong).

For the initial conditions it is necessary to impose them in the first time layer (I think they are in folder 0 when downloaded). You can increase your convergence if set correctly otherwise they might cause the simulation to diverge.

You can initialize your flow using the solution obtained from a steady simulation if you are running an unsteady simulation and if the initial transient is of no interest. One should always try to get initial conditions that are close to the solution which might be a hard job to do. Please add comments if necessary @PowerUsers_CFD.

Cheers and happy weekend!


Hi @tgraves @jousefm, if you want to consider elevation change then you will need a compressible analysis, where density can change, gravity is not assumed in any direction or magnitude, it needs to be specified under ‘model’.


@1318980, Where is the ‘model’ tab or option? I am confused on where to find it?

Tyler Graves

Hi Tyler,

there you go.




@jousefm. What kind of setting did you use to have the model pop up under the geometry primitives?

I realized that it is depended upon the turbulence model setting and it only pops up for me for LES Spalart-Allmaras and LES Smagorinsky and it only gives me a choice of inputting delta coefficient requirements.

What settings did you input to have the model give you the gravity inputs?

Thank You for your help.

Maria Chek

Hi @mchek,

that was a multiphase flow simulation example. As you already mentioned and noticed the gravity is not available in all modules! Are you working with the mentioned simulation types? Then there is no restriction to use the model option. Let me know if you have any further questions.