Thermal boundary layer measurements using planar laser induced fluorescence.


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An experimental arrangement of toluene-based Planar Laser Induced Fluorescence (PLIF) has been developed and applied to the study of free and impinging jets formed with air. In the toluene-based PLIF experiment, the flow is seeded with toluene particles and is illuminated using a laser light sheet. The high-temperature dependency of the toluene fluorescence signal and the temperature induced redshift of the toluene fluorescence spectrum, nominate it for quantitative thermometry applications. The toluene molecules are excited by absorbing a resonant photon from the laser and as a result fluoresce spontaneously. The fluorescence provides useful information such as the concentration and temperature of toluene particles and their surrounding environment. Two-color thermometry, with a single excitation wavelength (266nm) and camera image detection, is established for quantitative thermal characterization in this study. Simple free jets have been investigated to lead to refined data collection and data reduction. Time averaged, temperature profiles for the turbulent, free jets are obtained for jet Reynolds numbers of 5000, 10000, and 15000. To further validate the experimental technique, the jet temperature was varied from 300 K to 375 K. With the proposed data reduction methods, the PLIF technique was applied to a single impinging jet to assess both thermal flow field over a surface and convective transport from the surface. The PLIF method was validated against locally averaged Nusselt numbers using a traditional heat transfer calculation. PLIF results prove that PLIF can be applied to turbulent, near wall flows, where traditional methods are not able to non-intrusively measure the temperature gradient.



Planar laser induced fluorescence. PLIF. Toluene fluorescence. Toluene.