Abstract
The PIV method, which enables to measure instantaneous velocity distributions from visualized pictures of flow, was developed from the speckle method. The speckle method is not suitable to measure fluid motion. In order to generate clear speckle pattern, densely distributed micro-size irregularities are indispensable, whereas realizing such condition is difficult in fluid flow. PIV method was born by the idea of using actual particle image instead of speckle pattern. It enables us to measure fluid velocity distributions so efficiently than any other existing measuring method. And the measuring method has been achieving a great advancement in the last ten years. The advancement has been supported by the advancement of small computers, imaging instruments and lasers.
