Seaplane hull study : Boundary conditions problem

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July 21, 2020, 08:29
Seaplane hull study : Boundary conditions problem
#1
New Member

Leo
Join Date: Jul 2020
Posts: 3
Rep Power: 2
Hi all,

I am new to this forum, so please tell me if something is wrong in my approach.

I am working on a project for my master thesis, which aims to predict seaplane take-off performance doing some CFD calculations on Fluent in 3D, and to model the interactions between air and water.

To obtain my results, I am running transient calculations using K-Epsilon model. The problem is that the residuals and the calculations are converging (which is already a victory for me), but the results are wrong. I will explain myself.

After the initialization, almost everything looks fine : pressure is coherent (the distribution, not the values), velocity order of magnitude is coherent too, phases volume fraction, I do not see anything that could be wrong (I am doing an hybrid initialization from the inlet (or outlet) using the flat open channel initialization method).

After running the calculations, the results are not coherent with the boundary conditions I have set (At least the one I wanted to set). And the two things that are the most strange to me are first the pressure (the static one mainly), and the velocity. The pressure in water is evolving with depth (which is normal), but this is the same for air, and with the same evolution of pressure than water.
Concerning the velocity, the air is brutally accelerating at the outlet, right before leaving the fluid domain, and I have no explanation for it.
The boundary conditions I have set are a velocity inlet at the inlet with default values of turbulence, and I ticked open channel wave BC with none for the wave boundary conditions option. For the outlet, I have set a pressure outlet with the case open channel ticked, but what bothers me is that I haven't set any pressure anywhere in the boundary conditions, because of the multifluid conditions I had to set, which looks strange to me.

PS : The phases are more or less the same on after calculations
Attached Images
 Initial_Density.PNG (23.1 KB, 4 views) Initial_Pressure.PNG (31.1 KB, 3 views) Initial_Velocity.PNG (41.7 KB, 3 views) Pressure.PNG (51.7 KB, 4 views) Velocity.PNG (60.1 KB, 1 views)

 July 23, 2020, 21:06 #2 New Member   Join Date: May 2020 Posts: 9 Rep Power: 2 Brother im working on same problem. And my simulation does not even start. It gives me negative cell volume. Can u help me with this?

 July 24, 2020, 08:57 #3 New Member   Leo Join Date: Jul 2020 Posts: 3 Rep Power: 2 Hi, sorry but I have no exact idea of what your error message means, I think that I have read that it is about moving mesh which is moving too fast, but I am not using moving mesh. Please tell me if you find any solution about your calculations