Sailing Downwind: Aerodynamic Performance of the Velella Sail
| Autor: | Lisbeth Francis |
|---|---|
| Rok vydání: | 1991 |
| Předmět: |
Airfoil
Drag coefficient biology Meteorology Physiology Aerodynamics Aquatic Science biology.organism_classification Aerodynamic force Drag Insect Science Animal Science and Zoology Velella Molecular Biology Ecology Evolution Behavior and Systematics Geology Marine engineering Center of pressure (fluid mechanics) Wind tunnel |
| Zdroj: | Journal of Experimental Biology. 158:117-132 |
| ISSN: | 1477-9145 0022-0949 |
| DOI: | 10.1242/jeb.158.1.117 |
| Popis: | Using a wind tunnel built over a shallow pool and methods devised for measuring the performance of yacht sails, I describe aerodynamic performance in situ for the sailor-by-the-wind, Velella velella. By contrast with designers of the modern yacht mainsail, natural selection has apparently favored stability and seaworthiness over performance to windward. The Velella sail is a low aspect ratio airfoil with an unusually flat polar plot. Primarily a drag-based locomotory structure, this thin, leaf-like sail generates maximum force when oriented at attack angles between 50° and 90°. In the wind tunnel, free-sailing animals spontaneously assumed stable orientations at attack angles ranging from 28° to 87° and sailed with their hulls approximately broadside to the apparent flow of oncoming water. At these angles, aerodynamic force on the sail is asymmetrical, with the center of pressure upwind of the sail midline. Since aerodynamic force on the sail is balanced at equilibrium by hydrodynamic force on the hull, this orientation must be caused by asymmetrical forces acting on surface and underwater parts as the wind drags the animal along the surface of the water. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
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