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Hello, in this six-minute
video we are going to see how

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Heliciel sends a hydrofoil from
the designer to the CFD bench,

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and what the simulation
teaches us about its lift,

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its drag and the risk of cavitation.

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Here is the hydrofoil model
supplied with Heliciel:

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2 metres of span, a NACA 0006 profile,

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working in water at 4 metres per
second, half a metre under the surface.

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From the polar of its profile, the
designer calculates 926 newtons

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of lift for 32.5 newtons of drag:
a lift-to-drag ratio of 28.5.

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The PRO CFD menu exports
the foil to the test bench.

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Heliciel sends the geometry, the incidence
already contained in the drawing,

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and the fluid of the
project, with its density,

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its viscosity and its vapour pressure.

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The bench only receives half of the foil:

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it uses the symmetry to
calculate twice as fast.

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In the Flow tab, we check that the speed
and the fluid are those of the project:

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4 metres per second, and water at
999.7 kilograms per cubic metre.

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It remains to choose the mesh preset,

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and Heliciel announces its
duration before launching.

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For a drag, we take a
fine mesh: the Level 3.

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Two buttons, Mesh then Run
Solver; on a desktop PC,

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the whole calculation
took an hour and a half.

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Here is the calculated foil. Seen
from above, the upper face is blue:

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it is in low pressure, and it is this
suction that carries most of the load.

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Seen from below, the lower face is
slightly above the ambient pressure:

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it pushes, but much less
than the upper face sucks.

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A cut across the foil shows
what the polar does not show.

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The red spot at the leading
edge is the stagnation point,

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where the water comes to a
stop against the profile.

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Above it, the low pressure
spreads far into the water,

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well beyond the thickness of the profile.

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In velocity, the water
accelerates over the upper face,

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up to 6.3 metres per
second against 4 upstream,

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and leaves a thin wake
behind the trailing edge.

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The iso-surfaces wrap the zones where
the pressure drops below a threshold:

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they show how far, in the water, the low
pressure that carries the foil extends.

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And cavitation? Half a
metre under the surface,

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the ambient pressure is 104,900 pascals.

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The arrow on the left of the scale
marks the vapour pressure of water:

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1,300 pascals, where it
would start to boil.

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Even the lowest point of the
calculation, at the leading edge,

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stays around 86,000 pascals: at 4 metres
per second, this foil does not cavitate.

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The bench calculates 391 newtons of lift

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and 26.1 newtons of
drag on this half foil:

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about 780 and 52 newtons
for the whole foil.

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The lift is 16 percent below the
designer, the drag 61 percent above:

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a lift-to-drag ratio of
14.9 instead of 28.5.

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The gap is to be looked for
first on the mesh side,

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and the bench adds a warning:
at this Reynolds number,

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a laminar portion is likely
on the front of the profile,

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which the turbulence
model does not represent.

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The flow lines finally tell
whether the profile stalls:

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they would come off the skin and
roll up behind the trailing edge.

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Here, they pass over the foil in smooth
layers: the flow stays attached.

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Which mesh to choose?
The wing supplied with

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Heliciel has been calculated
with three presets.

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Level 1: 52,000 cells,
about a minute of meshing:

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10,557 newtons of lift, a
lift-to-drag ratio of 12.3.

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Level 2: 198,000 cells, 3 minutes:
10,735 newtons, a ratio of 14.0.

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Level 3: 811,000 cells, 28 minutes:

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the lift has only moved by
2 percent since the Level 1,

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while the drag has dropped by
17 percent, and the ratio reaches 15.1.

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For a lift, a fast mesh is enough;
for a drag, a fine mesh is needed.

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With Heliciel, a foil,
a wing or a fin goes

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from the drawing to the
CFD bench in one menu.

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We could now test a stronger incidence,

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and look at where
cavitation appears first.