The Thermal Boundary Layer Far Downstream of a Spanwise Line Source of Heat

Measurements are presented of velocity and temperature fluctuation statistics in two-dimensional boundary layers over nominally adiabatic, smooth, and rough surfaces far downstream of spanwise line sources of heat. All quantities are found to scale satisfactorily on u_τ, δ and ΔT_max. The generation term in the transport equation for the mean-square temperature fluctuation reaches a maximum at a distance of about 0.7δ above the surface and the turbulent Prandtl number is about 1.0 in the outer layer falling to zero near the surface. The outer part of the thermal layer behaves like a uniformly heated wall flow and the results are relevant to the central region of the plume from a point source of heat or pollutants, which will be approximately two-dimensional at large distances from the source.