Large-scale motions of thermal transport in high Reynolds number wall-bounded turbulent flows

Previous studies have found that there is a close correlation between the large-scale motions (LSMs) that mainly contribute to the momentum transport and the LSMs that transport most of the scalar fluxes. In our previous work, we found that LSMs that are responsible for momentum transport are similar to LSMs that transport heat. However, the study was done at a low-Reynolds number turbulent channel flow which does not closely represent actual cases. The proposed study investigates the shape and the size of LSMs in turbulent channel flows for a range of Reynolds. Particular emphasis is given to the physical size of the LSMs that carry most of the heat fluxes. A direct numerical simulation (DNS) databases of a turbulent channel flows up to friction Reynolds number (Re_τ) =5000 are used to visualize the structures. The LSMs are educed by using the three-dimensional iso-surfaces of cross-correlation coefficients of velocity and temperature fluctuations. Three-dimensional structures are computed at the different regions of the boundary layer to observe how the volume of the structures varies with the wall coordinate. This information is important for developing turbulence models and techniques for controlling flow and heat transfer in wall-bounded turbulent flows.