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-   -   VOF model with planning vessel (http://www.cfd-online.com/Forums/fluent/73144-vof-model-planning-vessel.html)

vmeertens February 28, 2010 14:03

VOF model with planing hull
 
Hi,

For my master thesis i have to study the flow around a speedboat.
In gambit i've created a flow volume and substracted the hull from that volume. The BC's are: Pressure inlet, pressure outlet and moving walls, the hull is a fixed wal.
The water flows from left to the right with a constant speed (30m/s).

In Fluent i've followed the next steps:

Steady Pressure based (Gravity enabled).
VOF with Realizable k-epsilon.
Material, phases, BC are defined the way it should be. (with specified density set to 0).
Solution methods: Scheme: Simple, Pressure: Presto, Momentum: Power Law, Volume Fraction: Modified HRIC, rest: Power Law.
Under-relaxation factors are decreased.
Initialization on Inlet.
start calculation.

When i check the results i get the following solution.

In a symmetry plane i want to see the contours of the 2 phases. When i plot them i get the following (with 2 phases):

http://i405.photobucket.com/albums/p...Final_Hull.jpg

There's no contact between the hull and the water. But the solution seems converged (Cl is constant and de residuals are converged till 10E-3)
The wave after the hull looks correct but the forces (lift and drag) are to big.

When i define 4 phases i get the following result:

http://i405.photobucket.com/albums/p...inal_Hull1.jpg

This seems a lot better but i cant give a physical explanation to 4 phases. :confused:

So my question is: are my calculations wrong or is this 'visual' result just a part of postprocessing and i shouldn't pay to much attention to the colors?

Thanks in advance!

Vincent

vmeertens March 1, 2010 08:29

I did a transient calculation after this, but it doesn't change anything to the results.

The initial water surface is set to y=0, so it should touch the hull in the middle. The hull is set under an angle of 2 (compared with pictures of the real boat)

-mAx- March 17, 2010 02:51

how did you initialize the vof (water)
Once the initialization is done, check the distribution of vof.
Does your free surface agree with what you want?

vmeertens March 25, 2010 16:49

Hey,

The vof is patched as following:

Adapt -> Region: dimensions of the volume of water.
Initialize from inlet
Patch -> Phase: water -> Volume fraction: 1 -> Hexadronr0
Patch -> X-Velocity -> Value: 30m/s -> Fluid

At t = 0 the free water surface is as it should be.

Now i'm doing the simulation with a better mesh thanks to mAx :)

Deepak Bansal August 9, 2013 16:12

air phase being formed on the bottom of the hull
 
hey buddy i am also facing same problem in planing craft that air phase being formed on the bottom of the hull.................how did u solve this problem.................reply as soon as possible...............


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