Large eddy simulations of variable property turbulent flow in horizontal and vertical channels with buoyancy and heat transfer effects

Turbulent combined flow of forced and natural convection was investigated using large eddy simulations for horizontal and vertical channels with significant heat transfer. The walls were maintained at constant temperatures, one heated and the other cooled, at temperature ratios of 1.01, 1.99, and 3.00, respectively. Results showed that with increasing the Grashof number, large-scale turbulent motions emerged near the wall, resulting in significant changes in turbulent intensities for the horizontal channel flow case. Aiding and opposing flows, however, for the vertical channel, emerge near the heated and cooled walls, respectively, while the pressure gradient drives the mean flow upwards. Buoyancy effects on the mean velocity, temperature, and turbulent intensties were observed near the walls. In the aiding flow, the turbulent intensities and heat transfer were suppressed and the flow was relaminarized at large values of the Grashof number. In the opposing flow, however, turbulence was enhanced with increasing velocity fluctuations.