A Profile Tracking System for Investigating the Behaviour of Discharges in Moving Environments

A pro®le tracking system (PTS) is developed to make measurements at previously inaccessible dimension-less distances from a discharge in a moving environment. With this system the measuring components remain stationary as the source is towed away from them. Image processing techniques are then employed to track concentration pro®les through a sequence of images, which are a constant distance from the ¯ow source. Data obtained from the PTS are shown to be both reliable and accurate. The bene®ts and limitations of the PTS when compared with normally con®gured laser-induced ¯uorescence systems are discussed. PTS is employed to gather data at dimensionless distances that are an order of magnitude greater than those previously obtained for the co-¯owing jet problem. List of symbols b spread of the jet c local mean tracer concentration C centreline mean tracer concentration C 0 initial tracer concentration C r jet centreline dilution H SCL horizontal scaling factor L E effective image length L I image length M e0 initial excess momentum of the ¯ow per unit density N p pro®les per image length O I initial image offset O F ®nal image offset t D sampling time per source location U a ambient ¯uid velocity U ar ambient to initial discharge velocity ratio u e magnitude of the local mean jet excess velocity U e magnitude of the centreline mean jet excess velocity x Cartesian coordinate in the same direction as the ambient velocity and the distance from the jet virtual source Dt pro®le sampling rate k difference in the width of the velocity and tracer concentration distributions 1 Introduction The behaviour of discharges into still and moving environments has been investigated experimentally for many years, but despite this long history there are still regions of discharge behaviour where our understanding of the ¯ow has not been con®rmed experimentally. This con®rmation has not been obtained because of limitations in experimental facilities and instrumentation. In recent years, relatively new optical techniques, such as laser-induced-¯uorescence (LIF) and particle image velocimetry (PIV), have provided the basis for very detailed studies into the behaviour of relatively simple discharge con®gurations. These studies have provided considerable insight into these ¯ows and an excellent example of this is the work of Papantaniou and List (1989). They employed LIF to conduct detailed investigations into the behaviour of jets and plumes in a still ambient ¯uid. The LIF technique has enabled investigators to obtain a more …