DOI: 10.1615/TSFP4
IDENTIFICATION OF THE NEAR-WALL FLOW STRUCTURES RESPONSIBLE FOR THE LARGE INSTANTANEOUS DEVIATIONS OF THE MOMENTUM AND HEAT TRANSFER ANALOGY IN A FULLY DEVELOPED TURBULENT CHANNEL FLOW
RÉSUMÉ
In this paper we analyze the spatial distribution of the instantaneous departures from the conventional analogy between momentum and heat transfer of a pressure driven fully developed turbulent channel flow at low Reynolds numbers (Re=4570, Pr=0.7). The analysis was carried out using a database obtained from a direct numerical simulation performed with a second-order finite volume code. The ensemble averaged velocity and temperature profiles and profiles of the turbulence intensities and turbulent heat fluxes agree well with direct numerical simulations available in the literature. When the flow was statistically fully developed, we recorded the time evolution of the velocities and temperatures near one wall of the channel. The near wall structures responsible for the extreme values of the deviations were educed by a conditional sampling technique. Results show that extreme values of the departures from the analogy occur within the imprints of the high-speed streaks on the wall and are associated with large positive fluctuations of the wall shear stress and wall heat flux. These large fluctuations on the wall are produced by the combined effect of two quasi-parallel counterrotating streamwise vortices.