A VIDEO IMAGE-ANALYSIS SYSTEM FOR CONCENTRATION MEASUREMENTS AND FLOW VISUALIZATION IN BUILDING WAKES

A video image analysis technique for concentration measurements and flow visualization was developed for the study of diffusion in building wakes and other wind tunnel flows. Smoke injected into the flow was photographed from above with a video camera, and the video signal was digitized in real time during the experiment and during playback with a video image analysis system. The relation between the digitized smoke intensity and the vertically-integrated concentration of smoke particles was obtained from calibration experiments in which the smoke was replaced by a mixture of ethane and air. The time-averaged vertically-integrated concentration of the ethane tracer was measured at discrete points throughout the flow field and correlated with the time-averaged smoke intensity data. After the system was calibrated, the instantaneous and time-averaged fields of vertically-integrated concentration were obtained by simply photographing the smoke plume. Color-contoured images of the plume were created and displayed in real time thus creating a pseudo-color movie that was very useful for flow visualization. This technique was used to study the effects of building geometry and source location on the concentration and flow patterns in building wakes.