Scalar dispersion from an instantaneous line source at the wall of a turbulent channel for medium and high Prandtl number fluids

Lagrangian methods have been used recently to reconstruct temperature profiles for relatively high Prandtl number, Pr, fluids (up to Pr=2400) in direct numerical simulations (DNS) of turbulent channel flow. The basic concept is that a heated surface is formed by an infinite number of continuous sources of heat. For example, the behavior of a heated plane can be synthesized by the behavior of an infinite number of continuous sources of heat that cover the plane. The building block for such a reconstruction is the behavior of a single instantaneous heat source located at the wall. The present work studies the behavior of such sources in turbulent channel flow. The trajectories of heat markers are monitored in space and time as they move in a hydrodynamic field created by a DNS. The fluids span several orders of magnitude of Pr (or Sc), Pr=0.1, 1, 10, 100, 200, 500, 2400, 7000, 15 000, 50 000, (liquid metals, gases, liquids, lubricants and electrochemical fluids). The effects of Pr in the evolution of the marker cloud are examined and quantified. The marker cloud is found to evolve in three stages, two of which are Pr dependent.