SimScale CAE Forum

Choosing between atmospheric pressure and velocity outlet

Hi everyone,

I’m new to this awesome program. I got a new project to design a new HVAC system. The program is easy to work with but I have trouble understanding the outlet parameters. I have an inlet and outlet duct with the SAME flow. I chose a velocity inlet with a speed of 2.5m/s. According to the HVAC sessions, they chose a pressure outlet instead of velocity outlet. Can you explain this choice please.

Session 1: Air-conditioning simulation of an office space:

Thank you in advance.

Hi @paulsaliba!

Valid question. Using the velocity condition in the inlet as well as the outlet is what is called a mathematically ill-posed problem as we cannot make sure that the exact prescribed value will be at the outlet - this has numerical reasons and is as well connected to the mesh resolution and quality.

We usually prescribe the pressure at the outlet or you can also define a mass flow rate on one side.

@1318980 & @Get_Barried, any additional thoughts here I forgot to mention?

Cheers,

Jousef