Development of high-resolution 2D-LIF temperature system: application on a non-isothermal turbulent jet

Laser-induced fluorescence (LIF) visualization techniques are used to quantify a wide range of aqueous flows, whether monophasic or two-phase. Depending on the resolution of the cameras used, these techniques generate a large amount of data that can be used to further study the behavior of a flow. The techniques use a laser sheet to stimulate fluorescent dyes seeded in the flow, resulting in fields of local measurements, depending on the thickness of the laser sheet, and offering a variety of possibilities for comparison with different digital resolution tools. Specifically, this paper presents a two-dye LIF (2D-LIF) temperature measurement system that exploits the variation of the photo-luminescence properties of two different fluorescent dyes with temperature, allowing quantitative measurement from the recorded fluorescence intensity. The system consists of high-resolution cameras (65 Mpxl) and a pulsed Nd-YAG laser, providing instantaneous and spatially resolved measurements. The present study describes the development of the 2D-LIF system and explains the choice of experimental setups for the most accurate and precise measurements. It then applies the system to measure the temperatures of several non-isothermal and turbulent jets. Time-averaged measurements are presented according to the physical model proposed by Morton et al. (1956), calibrated here with Particle Image Velocimetry (PIV) measurements. Radial turbulent temperature fluctuation distributions are estimated and compared in accordance with the literature.