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THE USE OF COMPUTATIONAL MODELLING IN A STUDY OF DOWNWIND SAILS Peter Richards and Gordon Mallinson...
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Transcript of THE USE OF COMPUTATIONAL MODELLING IN A STUDY OF DOWNWIND SAILS Peter Richards and Gordon Mallinson...
THE USE OF COMPUTATIONAL MODELLING IN A STUDY OF
DOWNWIND SAILS
Peter Richards and Gordon Mallinson
University of Auckland
New Zealand
Auckland - The City of Sails
Home of
The America’s Cup
The Yacht Research Unit
The primary function of the YRU is to co-ordinate and promote research and engineering activities within the University of Auckland that are related to yachts.
Images created by
Gordon Mallinson’s
package SeeFD
(Son of GRAFFIC)
Wind direction
America’s Cup Course
Wind Speed (m/s)
0
1
2
3
4
5
6
70
1020
30
40
50
60
70
80
90
100
110
120
130
140
150160
170180
190200
210
220
230
240
250
260
270
280
290
300
310
320
330340
350
34567
VMG maximum with a wind speed of 5 m/s
True wind direction
Wind direction
Spinnaker
Mainsail
Spinnaker pole
Boom
Spreaders
Masthead
Velocity Triangles
A
VT
VA
VB VT
VA
VB
A
(a) Boom Height (b) Masthead
Apparent Wind Twist
Test Section of Tamaki Twisted Flow Wind Tunnel
Schematic of Tamaki Twisted Flow Wind Tunnel
Test section
Honeycomb and mesh
25m
3m
Wind FlowFans
Wooden blocks
Pitot tube
Flow twisting vanes
(Not to scale)
Twisted flow?
Interaction Test Scenarios
Mainsail only Spinnaker only Combined sails
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
80 90 100 110 120 130 140 150 160 170 180 190
AWA (deg)
forc
e c
oe
ffic
ien
t
Av Cl Combined Av Cd Combined Av Cl Summed Av Cd Summed
Lift and Drag Coefficients - Wind Tunnel
-0.3
0
0.3
0.6
0.9
1.2
1.5
1.8
90 120 150 180
Apparent Wind Direction (degrees)
Fo
rce
Co
eff
ice
int
CD Spinnaker Both
CL Spinnaker Both
CD Spinnaker Only
CL Spinnaker Only
Lift and Drag on the Spinnaker - CFD
-0.3
0
0.3
0.6
0.9
1.2
1.5
1.8
90 120 150 180Apparent Wind Angle (degrees)
Fo
rce
Co
eff
icie
nt
CD Main Both
CL Main Both
CD Main Only
CL Main Only
Lift and Drag on the Mainsail - CFD
-0.3
0
0.3
0.6
0.9
1.2
1.5
1.8
60 90 120 150
Apparent Wind Angle (degrees)
Fo
rce
Co
effic
ein
t
CT Spinnaker Both
CS Spinnaker Both
CT Main Both
CS Main Both
CT Combined Both
CS Combined Both
Thrust and Side Forces: Spinnaker, Main and Both
-0.3
0
0.3
0.6
0.9
1.2
1.5
1.8
60 90 120 150
Apparent Wind Angle (degrees)
Fo
rce
Co
eff
icie
nt
CT Combined Summed
CS Combined Summed
CT Combined Both
CS Combined Both
Thrust and Side Force: Summed and Both
Twisted Onset Flow
-0.3
0
0.3
0.6
0.9
1.2
1.5
1.8
60 90 120 150
Apparent Wind Angle (degrees)
Fo
rce
Co
eff
icie
nt
CT Combined SummedCS Combined SummedCT Combined BothCS Combined BothCT Combined TwistedCS Combined Twisted
Thrust and Side Force: Summed, Both and Twisted
CONCLUSIONS• Both straight and twisted flow around a pair of
downwind sails have been modelled. • Under some sailing conditions there is significant
interactions between the sails, however under normal sailing situations this interaction is quite small.
• With twisted flow the thrust and side force coefficients are similar to those for straight flow if referenced to the masthead apparent wind speed and direction.