Aerodynamics

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Flow field around the mainsail & asymmetrical spinnaker at mid-height. The apparent wind speed is 3,3 m/s (6 kn) and angle 150°. The corresponding true wind speed is 6 m/s (12 kn).

Blue shades reflect pressures higher than athmospheric, orange and red lower pressures, green shades are neutral. An almost standing vortex is formed behind the mainsail, and two vortices behind the asym, from the luff and the leech.

http://www.wb-sails.fi/news/Ad_aerodynamics/images_ad_aero/Asy90-3lines.m4v

Flow behind a Finngulf 43 asymmetrical spinnaker at AWS= 2,6 m/s (5 kn) and AWA= 90 degrees.

At mid-height, the flow remains more or less in plane. At the foot and at the top, large vortices are formed. At the top, flow is bent upwards on the inside of the spinnaker and down on the outside, at the foot vice versa. Red colors denote accelerated flow, blue tones decelerated. The wind speed scale on the left goes from 1 m/s to 4 m/s. Note how the apparent wind gets stronger with height to begin with, simulating the surface boundary layer.