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January 16, 2024, 11:40 |
Single phase, gravity, incompressible fluid
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#1 |
New Member
Hi
Join Date: Jan 2024
Posts: 8
Rep Power: 2 |
I read some posts saying that the gravity has no effect on a single phase incompressible fluid since there is no variation of local density.
But if a fluid is at a certain height, the gravity source term should accelerate the fluid downwards, right? If I have a fluid on the moon, the fluid is just single phase, still it's going to accelerate. Another question; If I have an eulerian incompressible FVM solver, how could I do the simulation lagrangian? (the fluid starts to fall from a certain height and then it reaches the ground, a problem that seems tricky to be solved with eulerian) |
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January 19, 2024, 18:12 |
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#2 |
Senior Member
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If we split density in a constant + variable part, the gravity term with the former can be absorbed in the pressure, which means that your whole domain has a base acceleration and resulting pressure gradient, but no relative motion comes out from that.
Relative motion due to gravity, instead, requires non constant density in space. I try to interpret what you wrote and I guess you refer to liquids falling trough air, which indeed have different densities. Air would fall trough other air only if it is colder (with higher density) than surrounding air |
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January 19, 2024, 18:23 |
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#3 |
Senior Member
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I have now read some of your previous posts and better understand what you meant.
Vacuum is outside the validity limit of Navier-Stokes equations. Matter moving in vacuum under the influence of gravity is a completely different topic, that only under certain conditions can be retraced back to some form of fluid dynamic behavior. |
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January 20, 2024, 07:13 |
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#4 | |
Senior Member
Sayan Bhattacharjee
Join Date: Mar 2020
Posts: 495
Rep Power: 8 |
Quote:
In SU2-Nemo's conference videos for Martian atmosphere re-entry, they say that results from Navier-Stokes are not exactly correct. |
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