The thermal signature of a low Reynolds number submerged turbulent jet impacting a free surface

Abstract

The thermal signature of a low Reynolds number turbulent jet impacting a free surface was investigated experimentally. Three Reynolds numbers (1000, 3000, and 4800) were investigated for a configuration in which the jet nozzle diameter and the depth of the jet beneath the free surface were fixed. A high resolution infrared detector was used to collect thermal imagery of the surface temperature field. These data were then used to examine the detailed statistical nature of the resulting coupled thermal-hydrodynamic field. The analysis included an examination of the instantaneous, mean, and fluctuating surface thermal fields. Examination of the instantaneous fields strongly suggested the existence of a turbulent core region and a weaker outer region. The existence of this inner-outer structure associated with the surface flow was confirmed by a detailed examination of the mean surface temperature fields. In addition, the outer structure of the mean surface temperature appeared to correspond well with the existence of a surface current first observed by Anthony and Willmarth [“Turbulence measurements in a round jet beneath a free surface,” J. Fluid Mech. 243, 699 (1992)]. A self-similar region of the temperature field associated with the turbulent core was also clearly identified. Finally, the statistics of the surface thermal fluctuation fields were examined. These statistics revealed high thermal fluctuations near the edge of the flow field associated with flow intermittency there, as well as evidence of surface capillary waves which were generated as a result of the jet-surface interaction. In addition, the thermal fluctuation field was further examined using a Karhunen–Loeve analysis.