ペンギンの羽枝構造が持つ摩擦抗力低減効果

抄録

Since penguins prey underwater animals such as krills and small fishes, it must be important to minimize cost of swimming for the penguins. Their body surface was covered by aligned feathers of which barbs (i.e. branches of a feather) forms micro grooves similar to riblets. Here we investigate drag reduction effect of the barb structures by means of CFD (computational fluid dynamics) simulation. Firstly, we measured width and spacing of each barb for King penguin (Aptenodytes patagonicus), Humboldt penguin (Spheniscus humboldti) and Little penguin (Eudyptula minor) using museum specimens. As a result, it was found that the measured spacings were within the range of those of previouslyinvestigated riblets which reduces wall friction drag in turbulent boundary layer. Then, we created simple barb-likeriblets-models to perform static CFD simulations with RANS turbulence model using ANSYS Fluent, calculating the wall friction drag. As a result, the mimic model with spacing of 0.1 mm resulted in around 0.04% drag increase at 2 m/s flow speed, and around 0.02% drag reduction at 4 m/s flow speed in comparison with flat case. Therefore, it can be said that the barb structures in penguins are designed to prevent substantial increase in friction drag. It was also found that drag reduction effect was obtained even when incident angle of the flow increased up to 30°.