Analyzing 3-D Turbulent Motions in Open Channel Flow by Use of Stereoscopy and Particle Tracking

Abstract

Particle tracking is a conceptually simple method of obtaining quantitative velocity field information. Variations of the technique have been used for a long time, especially for liquid flows (Merzkirch 1987). We have taken a 3-d approach to the velocity measurement problem that uses stereoscopic recording and analysis of time sequence data in the manner of Chang, Watson & Tatterson (1985) and Sheu, Chang & Tatterson (1982) as well as Chiu and Rib (1956). The technique offers the capability of following the evolution of flow features in time. Data acquisition for the method relies on stereoscopic imaging of the positions of neutrally buoyant particles in a flow volume illuminated by a laser light source, and real time recording of the 2 video sequences of particle images. After digitization of the videotape sequences a photogrammetric analysis of each stereoscopic pair of images yields the 3-d particle positions in the object field. Particle centers are then tracked in space and time to obtain velocity vectors, particle paths, and extract information on the evolution of flow features of interest. We report here on our methodology and calibration procedures; results from our observations and analysis will be presented later.