The influence of bottom wall heating on the mean and turbulent flow behavior in the near wall region during mixed convection

An experimental work is reported that studied the effect of mixed convection on the mean and turbulent flow structure in the near wall region inside a horizontal square channel heated from below at low Reynolds numbers (Re) and high Grashof numbers (Gr). The Gr/Re² values ranged from 9 to 106 indicating that natural convection was dominant over forced convection for all studied cases. Velocity fields were measured using particle image velocimetry (PIV) in the vertical mid plane and two horizontal planes close to the heated wall. The results show that the bottom wall heating altered the mean velocity field and induced turbulence. Both mean and turbulent velocity magnitudes showed partial dependency on the Gr/Re² ratio. In the higher range of Gr/Re², mean streamwise velocity showed larger magnitude whereas, in the lower range of Gr/Re², streamwise and spanwise turbulent velocities have larger magnitudes. The streamwise and spanwise turbulent velocity magnitudes were also found to be largest close to the heated wall. It was observed that in the vicinity of the heated wall, the warm fluid converges along the streaks which initiate the rising plumes while the falling parcels of cooler fluid disperse in the spanwise plane.