Experimental investigation of the thermal field of a turbulent plume guided by a cylinder - preliminary results

This investigation analyses the turbulent structure of a thermal plume created by a heated disc, evolving in a neutral environment and guided by a vertical cylinder located 1 cm above the level of the hot source. The objectives of the study were to understand the development mechanisms of this buoyancy driven flow and the effect of the vertical cylinder on the horizontal entrainment of the plume. The experimental results show clearly a change of the turbulent structure of the flow in comparison with the free plume. This difference is especially characterised by the strong decrease of the mean axial temperature near the source and the appearance of two symmetrical maxima resulting from vortices of hot air that divide the flow in two symmetrical regions separated by a region fed by fresh air. This phenomenon is also observed for the turbulence statistics. The skewness and flatness factors of the temperature fluctuations show that the latter have a nearly Gaussian distribution in the most turbulent regions of the flow, but that deviates gradually from the Gaussian distribution in the regions where the amplitude of the temperature fluctuations decreases.