1) Example for negative angle of attack

Abbildung 1: Deformation of sail during unsteady computation

In Fig.1 an animation of the sail shape is given (line in the middle. The other lines from top to bottom represent block interfaces moving according to the grid deformation). The initial shape is arbitrary, which has to be taken into account for the itarative computation of the sail shape, as the process has to be underrelaxed when this initial shape is far from the final solution. Using a solution from another computation for the same sail at a similar angle of attack as a restart, this is not necessary anymore.

Abbildung 2: Distribution and isolines of velocity in x direction (negative values in blue)

Fig.2 depicts the finally steady ditribution and isolines of velocity in x-direction. Taking an even smaller angle of attack than this one (2.5°), the sail snaps through which cannot (yet) be handled by the algorithm.

Abbildung 3: Deformation of Navier-Stokes Grid

The grid deformation, Fig.3, is computed using a structure mechanical analogy

Literaturnachweis

[1] Bunge, U.; Rung, T.; Thiele, F.:  A two-dimensional sail in turbulent flow, Fluid Strucrure Interaction, Chakrabarti, S. K.; Brebbia, C. A. (Eds.), pp. 245-254, Series: Advances in Fluid Mechanics, Vol. 30, WIT Press, Southampton, Boston, 2001, ISBN 1-85312-881-3, presented by Bunge, U. on Fluid Strucrure Interaction 2001 in Chalkidiki, Greece, September 2001