Abstract
An obstacle in fluid is subjected to hydrodynamic drag force. It is important to reduce the drag force to save energy and to prevent fluid machinery from breaking. We investigated drag-reducing effects of surfactant additives in flows around circular and square cylinders. We performed PIV measurements in the wake region of circular and square cylinders and visualized the free surface around circular and square cylinders. Surfactant addition in flows resulted in making vortices weak and reducing oscillation of free surface in the wake region.
