Thermal structure of a flat plate turbulent boundary layer diffusion flame has been investigated experimentally. Measurements of fluctuating temperatures and fluctuating velocity have been made, using an electrically compensated fine wire thermocouple and a laser-Doppler velocimeter respectively. Results show that a profile of turbulent intensity of temperature fluctuation has two maxima and one minimum. The minimum is located at the station where the gradient of mean temperature is zero. On the other hand, gradients of mean temperature at stations of two maxima are very high. In the region between the flat plate and the flame, the thermal structure is characterized by low frequency fluctuations, which are mainly attributed to fluctuations of the reaction rate at the reaction zone. In the region between the flame and the edge of the thermal boundary layer, the thermal structure is characterized by high amplitude and high frequency temperature fluctuations, which are mainly caused by the mixing of hot and cold gases.
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