A comparison of downwind sail coefficients from tests in different wind tunnels

Campbell, Ian

doi:10.1016/j.oceaneng.2014.06.036

Cited by 13 publications

(5 citation statements)

References 4 publications

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“…This is not unusual for downwind yacht sails (Viola, 2013). For example, America's Cup sails are typically tested in wind tunnels at Re of the order of 10 5 (Campbell, 2014a), and the predicted performances are in good agreement with those observed with full-scale trials (Campbell, 2014b). At the conditions tested in this study, the flow is fully separated at the sharp leading edge, and thus the effect of a lower Re is expected to be moderate.…”

Section: Introductionmentioning

confidence: 55%

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Vortex flow of downwind sails

Arredondo-Galeana

Babinsky²,

Viola³

2023

Flow

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This paper sets out to investigate the vortex flow of spinnaker yacht sails, which are low-aspect-ratio highly cambered wings used to sail downwind. We tested three model-scale sails with the same sections but different twists over a range of angles of attack in a water tunnel at a Reynolds number of 21 000. We measured the forces with a balance and the velocity field with particle image velocimetry. The sails experience massively separated three-dimensional flow and leading-edge vortices convect at half of the free-stream velocity in a turbulent shear layer. Despite the massive flow separation, the twist of the sail does not change the lift curve slope, in agreement with strip theory. As the angle of attack and the twist vary, flow reattachment might occur in the time-average sense, but this does not necessarily result in a higher lift to drag ratio as the vorticity field is marginally affected. Finally, we investigated the effect of secondary vorticity, vortex stretching and diffusion on the vorticity fluxes. Overall, these results provide new insights into the vortex flow and associated force generation mechanism of wings with massively separated flow.

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Section: Introductionmentioning

confidence: 55%

“…This is not unusual for downwind yacht sails (Viola, 2013). For example, America's Cup sails are typically tested in wind tunnels at of the order of (Campbell, 2014a), and the predicted performances are in good agreement with those observed with full-scale trials (Campbell, 2014b).…”

Section: Introductionmentioning

confidence: 61%

Vortex flow of downwind sails

Arredondo-Galeana

Babinsky²,

Viola³

2023

Flow

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“…Wind tunnel is commonly used to control the aerodynamic and motion environment of yacht. It has been subject to a large number of experimental studies to measure both the aerodynamic loads on the boat frame using a balance (Flay, 1996;Viola and Flay, 2009;Fossati and Muggiasca, 2011;Campbell, 2014) and the pressure and 3D shape deformation of the structure (Graf and Müller, 2009;Viola and Flay, 2011;Viola et al, 2013). Recent studies have highlighted the non-trivial effect of dynamic oscillation on the aerodynamic forces (Gerhardt et al, 2011;Fossati and Muggiasca, 2011;Augier et al, 2013Augier et al, , 2014a.…”

Section: Mavmentioning

confidence: 99%

Experimental analysis of a strong fluid–structure interaction on a soft membrane—Application to the flapping of a yacht downwind sail

Deparday

Augier

Bot

2018

Journal of Fluids and Structures

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“…However, wind tunnel testing and full-scale testing are required for comparison and validation (Hansen et al 2002;Viola and Flay 2011;Renzsch and Graf 2013). Wind tunnel testing has the advantage of being in a controlled environment where a balance can be used to measure the forces created by the sails on the boat frame (Flay 1996;Zasso et al 2005;Graf and Müller 2009;Campbell 2014b). These results can easily be used to create a Velocity Prediction Program (Le Pelley and Richards 2011;Campbell 2014a).…”

Section: Awamentioning

confidence: 99%

Modal Analysis of Pressures on a Full-Scale Spinnaker

Deparday,

Bot,

Hauville

et al. 2017

Journal of Sailing Technology

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While sailing offwind, the trimmer typically adjusts the downwind sail "on the verge of luffing", occasionally letting the luff of the sail flap. Due to the unsteadiness of the spinnaker itself, maintaining the luff on the verge of luffing requires continual adjustments. The propulsive force generated by the offwind sail depends on this trimming and is highly fluctuating. During a flapping sequence, the aerodynamic load can fluctuate by 50% of the average load. On a J/80 class yacht, we simultaneously measured time-resolved pressures on the spinnaker, aerodynamic loads, boat data and wind data. Significant spatio-temporal patterns were detected in the pressure distribution. In this paper we present averages and main fluctuations of pressure distributions and of load coefficients for different apparent wind angles as well as a refined analysis of pressure fluctuations, using the Proper Orthogonal Decomposition (POD) method. POD shows that pressure fluctuations due to luffing of the spinnaker can be well represented by only one proper mode related to a unique spatial pressure pattern and a dynamic behavior evolving with the Apparent Wind Angles. The time evolution of this proper mode is highly correlated with load fluctuations. Moreover, POD can be employed to filter the measured pressures more efficiently than basic filters. The reconstruction using the first few modes makes it possible to restrict the flapping analysis to the most energetic part of the signal and remove insignificant variations and noises. This might be helpful for comparison with other measurements and numerical simulations.

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A comparison of downwind sail coefficients from tests in different wind tunnels

Cited by 13 publications

References 4 publications

Vortex flow of downwind sails

Vortex flow of downwind sails

Experimental analysis of a strong fluid–structure interaction on a soft membrane—Application to the flapping of a yacht downwind sail

Modal Analysis of Pressures on a Full-Scale Spinnaker

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