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These movies
are from a wind tunnel research program we recently
carried out at the HUT
and VTT
wind tunnels. The purpose of the research was primarily
to calibrate and verify the MacSail
aerodynamic simulation program. The effect of the hull
& rigging on the air flow over the sails was studied,
and insight was gained on the influence of various trim
lines such as sheets, cunningham, outhaul, mast bend
etc.
The trailing vortex emanating from the upper
leech of the jib can clearly be distinguished above
the leeward back corner of the model. The yarns on the
windward side lie relatively still compared to the disturbed
flow in the jib wake on the leeward side.
Flow separation is monitored with 10 mm long tell tails
cut from regular C-cassette tape. The wind speed is
15 m/s (30 kn).
Alternative JPEG
movie, should the better quality Quicktime movie
not work for you.
A closer view reveals some intermittent separation
in the upper leech of the main. The separation is at
least partly triggered by the jib wake vortex interfering
with the mainsail flow.
Alternative JPEG
movie, should the better quality Quicktime movie
not work for you.
Even closer, the turbulent nature of separated
flow is clear. See also the yellow tuft at the jib leech,
and the disturbance of the mast over the tell tail close
to the luff. In see through, you can distinguish the
windward tell tail streaming straight up.
Alternative JPEG
movie, should the better quality Quicktime movie
not work for you.
The tests were carried out in wind speeds ranging from
10 to 20 m/s (20 to 40 kn). Wind speed was chosen to
generate sufficient pressure to provide realistic mast
bend & sail cloth stretch properties. The model
is equipped with all normal sail controls including
sheets, cunninghams, outhaul, jib lead, traveler &
boom vang.
The sail trim was radio controlled from outside the
tunnel, while actual sail driving force, heeling force
and heeling moment could be read on the computer screen
during the test. Depending on the test run, sail drive
(light to medium air tests) or the sail drive to heeling
moment ratio (heavy air tests) was maximized.
20 different runs were carried out, with tens of measurements
in each run at apparent wind angles ranging from 18
to 60 degrees (corresponding to a true wind angle range
of approximately 35 to 90 degrees). The sail shape &
tell tail behavior was recorded during each run with
3 video cameras and one normal camera. More than 15
hours of video was recorded during the tests, for later
analysis
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The
movies were made using Apple's Quicktime
- they should
run under
Windows, too, at least in newer browsers (4+). |
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