Drag Reduction and Its Application. Drag Reduction Caused by Traveling Wave Occurring on the Surface of Elasto-Flexible Cylinder.

Abstract

It is important to fluid mechanics and bio-fluid mechanics to understand an interaction among deformable surface, its surface, its surrounding flow field and hydrodynamical forces. In order to clarify this interaction by experiments, we have been using several cylinder models having an elasto-flexible surface in uniform water flow. The hydrodynamic forces were measured by a three-component force balance. The deformation of the surface and the flow field around it were visualized using a laser light sheet method simultaneously. The experimental results showed that the time-averaged hydrodynamical drag was approximately 20% lower than that of the rigid cylinder when the continuously occurring wave appeared on the surface. In the case of the drag reduction occurrence, the power spectra of the lift fluctuation were broadened and had several peaks. In particular, the prominent frequency of power spectrum was about 45% lower than the frequency in the cases of the rigid cylinder and of no drag reduction occurring. The visualization results suggested that the strength of the Karman vortex shed from the cylinder was decreased compared with that from the rigid cylinder and this decrease was responsible for the above mentioned drag reduction.