Different results with same configuration in fluent analysis
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- Last Post 16 January 2020
The second set of results are nonsense: what's the convergence like on that model? I'd also suggest checking you've got enough mesh to resolve the flow, what's the speed of sound in your system?
I don't know where verify the convergence of my model. Considering the trend of the residuals graph during the calculation the convergence is not so far, however i don't modify my setup from atomatic calculation to manual calculation, so i shuld have the same results. I did not modify manually my speed of sound, i only set my air density like "real gas" and my air viscosity like "kinetic theory" in materials properties. I chose the mesh sizing with maximum number of nodes allowed by student license.
Why are you using real gas? Please review the tutorials/YouTube to see how convergence is checked.
I'm using real gas because i must consider a real system with atmospheric air, including losses pressure values in internal pipelines
Read the definition & use of real gas carefully: are you trying to capture the JT effect?
I read the ansys online guide and chose the Aungier-Redlich Kwong real gas model to define my air properties. I'm not considering the JT effect
Try again with ideal gas: unless you're at a very high pressure and/or expecting to need JT or phase change I'd not use real gas.
I have high pressure value in my system, so I can't consider air like ideal gas. however I tried to set air like ideal gas and run calculation, but i have always the same problem (different results if I run design points automatically or manually)
Do you have pressure boundaries on both ends of the domain? If so, the mass flow becomes part of the solution which makes the solution much more dependent on the initialisation values. Looking at your "good" results, how much mesh have you got to resolve the 350m/s velocity region? What do you count as "high pressure"?
I have a pressure input boundary and a atmospheric output boundary (I set outlet-vent). I have 3 atm pressure value in my system.
Outlet vent has some additional parameters, if the outlet is to atmosphere pressure outlet may be more suitable.
3atm isn't an overly high pressure: flow will probably choke but that's about it. If you'd been talking about 60-500 bar then I'd agree it was a high pressure application.
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