[vmeertens]

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):



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:



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

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]

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-]

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]

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]

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...............