On Information Quantity about Flow Fields Based on Visualizing Photographs by Tuft Method

The main purpose of the visualization of flow by tuft method is to know the direction of flow and the extent of separation zone in the parts along objects and channel walls in the case of surface tuft method, and the wind direction distribution in the cross section of the wake behind objects and the flow in channels in the case of tuft grid method. Accordingly, in the past the sketch added with visual observation and proper recording as far as possible was the best observation method and recording method. However, naturally this method has made the information on flow from the result of visualization by tuft method into a qualitative thing. Recently, by the progress of photographic techniques, video technology and image analysis method, the reading of the angles and dimensions of the objects from their photographs and video image has become able to be accurately carried out. If tufts are in the state of completely following the flow at their attaching points, it may be considered that the tufts indicate the quantitative condition at that time of the wind velocity, wind direction, pressure and so on in a flow field. Accordingly, by analyzing the positions and motion of those tufts, the condition of a flow field can be known quantitatively. Since photographs and images are those of mapping tufts from three-dimensional space to two-dimensional space, the information quantity about a flow field exists in photographs and images in the compressed condition. Accordingly, if tufts are made and photographs are taken for the purpose of obtaining the quantitative information, the information on a flow field can be known quantitatively. This report gives one example showing that the swirling flow in a pipe, in which steady flow and unsteady flow exist in mixed state, is visualized by tuft grid method, and by using the photographs taken, the information on the flow field can be obtained quantitatively. In particular, it is shown that in the part where flow is steady, only from the photographs taken in one direction, the quantitative information can be obtained with considerable ■curacy