VISUALIZATION AND ANALYSIS OF BOUNDARY LAYER FLOW IN LIVE AND ROBOTIC FISH

摘要

Near wall flow over both live and robotic fish was visualized using a pulsed laser sheet and a high-resolution digital video camera. Velocities of particles illuminated by the laser sheet were determined by particle tracking, PTV. Particles very close to the fish surface, y < 1 mm were tracked semi-automatically, while those further away were tracked automatically using a particle finding and matching algorithm. Standard cross-correlation DPIV (digital particle imaging velocimetry) was also used as a crosscheck. The outline of the fish surface was fit with an appropriate spine so that u and ν velocity profiles could be constructed with respect to the curved fish surface. The technique allowed for the resolution of the viscous sublayer. The boundary layer flow over live and robotic fish was not always easily categorized as laminar or turbulent when compared to accepted flat plate profiles. Deviations from flat plate theory are not surprising, however, considering the waving motion of the fish surface. Resolution of the fish boundary layer is an essential part of examining possible drag reducing techniques involving the manipulation of near wall flow.