Coupled temperature and velocity measurements in turbulent natural convection flows

The goal of this paper is to develop simultaneous measurements of the temperature and velocity in order to contribute to the development of models adapted to natural convection flows and better apprehend their turbulent characteristics. The experimental setup consists in a vertical open channel whose sidewalls are kept at ambient temperature. A heated square bar is placed into the lower part of this channel close from one of its wall. It drives air in the whole channel The temperature of the bar is chosen to obtain a turbulent air flow. This study focuses on the measurement technique developed to realize synchronized temperature and velocity measurements in a turbulent natural convection flow. This technique permit to measure turbulent heat fluxes (< u'T'> or < v'T'>). Measurement strategies will be presented and discussed in the paper. Some experimental care is needed to avoid disturbing the airflow. The challenge is to choose two complementary measurement techniques which have to be synchronized but which cannot be carried out at the same location when a laser is used. In this study, the velocity and the temperature measurements are respectively carried out using PIV technique and a specific K type micro-thermocouple (12.7 mu m in diameter). The location of the thermocouple with respect to the laser sheet has been investigated as well as the influence of the laser on the temperature measurements. The criterion used for finding the best location is the correlation coefficient between the temperature and the velocity data. Some preliminary results of coupled velocity-temperature measurements are provided showing the feasibility of this kind of measurements.