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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.

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.

1 Comment

  1. Claes Johnson Jul 23, 2009 Reply

    A new explanation of the action of a sail based on advanced computation of turbulent solutions to the Navier-Stokes equations is presented in sequence of knols under Applications on

    as a part of My Book of Knols on

    including references to supporting scientific articles.

    We show that classical explanations of the action of sail are incorrect or un-physical, and we exhibit the true mechanism generating lift and drag of a sail. See also my blog:

    Any comments are wellcome.


    Claes Johnson

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