(232o) Effects of Velocity Structure On Turbulent Heat Transfer From the Wall

This work involves numerical experiments that were conducted in a turbulent channel flow using Direct Numerical Simulation (DNS) in conjunction with the tracking of thermal walkers released from the wall of the channel in this flow field. This is a Lagrangian approach to the dispersion process. Insights about the mechanism of turbulent transport can be obtained by observing the behavior of heat markers that are released from a single instantaneous line heat source.

The goal is to investigate the correlation between the velocity and the temperature field in wall turbulence. The simulations were conducted in a computational box of dimensions 3800x600x1900 in viscous wall units, and for different Prandtl number fluids (Pr = 0.1, 0.7, 6, 20, and 50). The half channel height in viscous wall units was h = 300. Each computation was repeated for 5 different initial velocities of the flow field, in order to release heat in independent velocity field. The total number of the heat markers was 260,100, and they were released from a single line source at the wall. The trajectories of the heat markers were monitored in space and time as they moved through the channel. The behavior of these heat markers was observed in 12 successive locations downstream form the source ranging from h to 12h. In each of these locations the flow structures that carried thermal markers towards the channel center (i.e., those that transfer heat away from the wall) and flow structures that carried thermal markers towards the channel walls (i.e., those that transfer heat towards the wall) were studied as a function of the Prandtl number. The characteristic length scales of the flow that are contributing most to heat transfer were determined based on these structures. The characteristic time scales were obtained based on the calculation of Lagrangian correlation coefficients for the markers that are captured in each of these downstream locations.