Learning Forum

[Gennadii]

Hi, evryone.

Help me understand what the "pressure outlet" boundary condition means. What condition is imposed on the pressure in this feature? There is no backflow, zero gauge pressure, reference pressure 1 atm.

In the theory guide, p. 618, "14.3.10.2.1. Pressure Outlet," it is written: "Gauge Pressure: The static pressure is a user-specified value."

Thus, I could expect that this boundary condition imposes a pressure value defined by the user, in my case 1 atm. However, my model includes additional heat sources that increase the temperature, which also raises the pressure. As a result, I observe a pressure significantly higher than 1 atm at the outlet.

So, what exactly is the condition imposed on the pressure in the outlet region?

[Rob]

It's what you want at the outlet, ie what is "outside" of your domain. So if you expect to pressurise the domain you may need to change the value. 

[Gennadii]

Hi Rob,

Thank you for your response.

Could you please explain (or point me to relevant resources) how it is possible for the "outside" pressure to be 1 atm while the outlet pressure is 2 atm? This suggests that some form of transition must occur between the outlet and the "outside" region.

For example, in the case of temperature, the outlet boundary condition typically imposes a zero flux, meaning there is no temperature gradient across the outlet, so the "outside" temperature becomes equal to the outlet temperature. How does this work for pressure? How is the step transition handled, and how does it influence the outlet pressure?

Thank you in advance.