Experimental characterization of a free thermal plume and in interaction with its material environment

Abstract

Abstract This investigation analyses the behaviour of a turbulent thermal plume evolving in a neutral environment and in interaction with its surrounding material. The thermal plume is created by a rectangular hot source. This source is placed at the entry of a vertical parallelepipedic canal opened at the ends. Firstly, we studied the behaviour of a free thermal plume. The flow visualization and the analysis of the thermal and dynamic fields enabled us to detect the existence of two zones during the vertical evolution of the plume. A first zone of plume development followed by a zone of established turbulence. Secondly, we described the structure of a thermal plume produced by the same source inside the vertical canal. In this case the experimental results show clearly a change of the turbulent structure of the flow in comparison with the free plume. This difference is especially characterized by the appearance of a supplementary zone just above the source that is added to the two zones described previously. In addition, the comparison of the two studied configurations showed that the structure of the plume is narrowly affected by the confinement. In order to better define the fine structure of the flow, the temperature fluctuations spectra are analyzed. This spectral analysis enables us to show the fast destruction of the big structures vortexes by the confinement effect to give a smaller structure.