Scalar transport from a planar source in a turbulent boundary layer

The dispersion of a passive scalar in a turbulent boundary layer has been investigated experimentally in a wind tunnel. Heat was used as a passive scalar based on the fact that the mass and heat diffusivities for gases are of the same order. For that purpose, a planar heat source was mounted on the surface of a flat plate and consequently, the heat released was carried downstream by the plate's boundary layer. Hot wire anemometry with a specially designed triple-wire probe was employed for the direct measurement of two turbulent heat flux components and a momentum flux component. Measurement of the normal (to the plate) heat flux led to the determination of the eddy diffusivity of heat directly from the experimental data. The experimental data were further analyzed by the quadrant-splitting technique. It was found that primarily, heat was carried by only one basic fluid motion, the “ejections”.