Multiscale analysis of heat transfer in fully developed turbulent channel flow

An analysis is given for fully developed thermal transport through a wall-bounded turbulent fluid with constant heat flux supplied at the boundary. The analysis proceeds from the averaged heat equation and utilizes, as principal tools, various scaling considerations. The paper first provides an accounting of the relative dominance of the three terms in that averaged equation, based on existing DNS data. The results show a clear decomposition of the turbulent layer into zones, each with its characteristic transport mechanisms. There follows a theoretical treatment which justifies and greatly extends these empirical results. The main hypothesis in this development is the monotone and limiting dependence of the difference between the specially scaled centerline and wall temperatures on the Prandtl number, a fact well corroborated by DNS data. A fairly complete qualitative and order-of-magnitude quantitative picture emerges for a complete range in Prandtl numbers. It agrees with known empirical information. In a manner similar to previous analyses of turbulent fluid flow in a channel, conditions for the existence or nonexistence of logarithmic-like profiles are found.