December 1, 2018 at 1:08 pmAndreaSubscriber
I'm simulating a closed aluminum box filled with air, 2D setup.
I increase the temperature of the air inside the box and given that the volume is closed I would like to observe increasing temperature and pressure at constant density.
What actually happens is that the temperature rises but the weighted-average-area density (and the mass as consequence) of the fluid drops. Slightly changing the setup I can observe an increase in pressure but still a considerable density (mass) reduction.
The ways I tried heating the gas inside are the following(used every one alone):
- heat source in the gas;
- heat source in the solid (thick box surrounding the fluid);
- heat flux across the interface solid-fluid;
- convection of heat from the outside of the box enclosure.
- pressure-based/transient/velocity formulation:absolute/Planar
- viscous model SST k-omega(to simulate natural convection inside the box)/energy: on/ S2S radiation
- BC: in a compatible way with the above heating "strategies" I set: thermal coupling in the solid-fluid interface, adiabatic condition in the outside wall of the enclosure
- IC: (standard) T=273K, operating pressure=1bar, turbulent kinetic energy and specific dissipation rate: 1
- air density: ideal gas law
- The mesh is done with quads, bi-exponential growth ratio of 1.15 both in solid and fluid, so close to the wall I have a nice boundary layer
- scheme: coupled [also tried Simple]
- gradient: green-gauss
- Pressure: PRESTO! [also tried Second order]
- others: first order upwind
IN the attached picture the heat sources is located in the fluid.
I have no Idea why I'm losing mass (not even displayed in the mass balance flux in the postprocessing section).
Any guess, advice is very welcome! It's so frustrating not be able to verify the IGL with fluent.
December 3, 2018 at 5:55 pmDrAmineAnsys Employee
Switch on floating operating pressure and use a sensible time step size like sqrt of a minimum of cell thickness divided by a thermal gravity. Thermal gravity is isobaric thermal expansion times maximum temperature differences times the earth acc.
December 3, 2018 at 6:54 pm
December 3, 2018 at 7:57 pmDrAmineAnsys Employee
It would require some UDF programming to mimic Fluent behavior when working with real gas: you need to adjust the operating pressure every iteration like Fluent.
December 3, 2018 at 8:04 pmAndreaSubscriber
Ok, so in this case I would get the density properly computed with the real gas model and I could adjust the operating pressure with the ideal gas law for example.
It seems quite challenging but I will try for sure. Thank you again!
- You must be logged in to reply to this topic.
Simulation World 2022
Earth Rescue – An Ansys Online Series
- Suppress Fluent to open with GUI while performing in journal file
- Heat transfer coefficient
- What are the differences between CFX and Fluent?
- Floating point exception in Fluent
- Time Step Size and Courant Number
- Difference between K-epsilon and K-omega Turbulence Model
- The solver failed with a non-zero exit code of : 2
- Floating point exception
- How to model free convection warming of liquid in a plastic bag