Feasibility study on water flow visualization using cellulose particles and pervasive display

Understanding water flow around a swimmer is key to reducing the water resistance when swimming and improving propulsive force, since swimmers who produce less turbulent flows around their bodies can, for example, swim faster. However, existing water flow measurement technologies are not suitable for measuring human swimmers because they can only measure a limited area and have potential adverse health effects on swimmers. In this research, we propose a harmless method of water flow measurement using food-grade particles and a harmless light source. To visualize the movement of water, cellulose particles (microcrystalline cellulose) are introduced into the water. We use an optical property of cellulose particles, called birefringence, which becomes brighter than its surroundings when placed between right and left circularly polarized plates and which enables flow measurement by using an existing particle tracking method. The proposed water flow measuring technology aims mainly at enhancing swimming training. However, this technology could also contribute to the advancement of human-computer interaction underwater and to education on basic fluid dynamics more generally. To test the capabilities of the proposed water flow measurement technology for measuring slight water flows, such as turbulent flows, we prepared objects of various shapes, including a spherical object (high resistance), streamlined objects (low resistance), and a human-shaped doll posed in several swimming forms, and put them into a water tank with a steady water flow. Expected water flows were observed and measured using the proposed flow measurement technology.