An image processing technique for determining two-dimensional flow fields with reverse flow

A specific technique based on the digital image processing approach has been developed for analyzing the two-dimensional flow field from pathline photographs. This technique requires that two important problems are solved. The first problem is to distinguish the intersecting pathlines, and the other is to determine the flow direction. This paper proposes two methods of overcoming these problems. The first is the method of analyzing three photographs obtained by two electrically controlled cameras. The three photographs show pathlines, initial and terminal positions of trace particles. The velocity vectors are easily determined by superposition of these photographs. The second is the method of utilizing a photograph which contains pathlines obtained by short exposure and its initial positions by instantaneous flash. These two methods are applied to two-dimensional water flow around a circular cylinder and the velocity fields with reverse flow are extracted automatically through the micro-computer system.