Str�mungsanpassung des Pinguins beim Schwimmen unter Wasser

Abstract

Penguins (Pygoscelis papua) swimming parallel to the glass screen of a large aquarium in Zoologischer Garten, Frankfurt, were filmed during deceleration phases during which their extremities were not moved relative to the trunk. Drag coefficients were determined using a newly developed method of analysis (the reciprocal value of velocity plotted as a function of time gives a linear curve during undisturbed deceleration). The frontal drag coefficient is 7·10−2, surface drag coefficient 4.4·10−3 and volume drag coefficient 3.1·10−2. The ratio of length to diameter is 4.2. The length from head to broadest part of trunk relative to body length is 0.48. These results are compared with technical hydro- and aerodynamic measurements found in literature. The body form of penguins appears to be well adapted to transporting unit mass with least resistance. Their frontal and volume drag coefficients cannot be further improved. The surface drag coefficient shows that, at Reynolds numbers of deceleration swimming (Re≈106), unusual effects need not be taken into account. This indicates that the boundary layer is partly laminar, partly turbulent as found in optimally stream-lined technical objects. We suppose that the smooth feathered surface of a penguin dampens boundary layer oscillations especially during fast swimming at Reynolds numbers of 107 and guarantees laminar flow over larger regions of the trunk.