Mass transfer analogies have long been used to experimentally determine the distribution of cooling fluid through pointwise sampling for turbine blade, nozzle or combustor film cooling. The behavior of a turbulent jet or plume flowing into its surroundings cannot be fully understood from point measurements alone, however. Full-field measurement of the instantaneous distribution of cooling fluid can reveal the structure and mechanisms governing cooling performance. This paper describes an improved dual light sheet PLIF (Planar Laser Induced Fluorescence) technique developed for full field concentration measurements. An analytical model of laser light sheet / fluorescent dye interaction was formulated and used to evaluate the light sheet attenuation corrections. With the more common single light sheet technique, these corrections lead to substantial concentration uncertainty which can be substantially reduced by using a dual light sheet. The dual light sheet technique was used to study the time-varying position and area of concentration isopleths for a round jet issuing into quiescent surroundings. Results show that, although concentrations at any point vary widely with time, the area within a given concentration isopleth remains virtually constant.

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