Faculty Publications
Raman Scattering Measurements In The Initial Region Of Sub- And Supercritical Jets
Abstract
A high-pressure chamber is used to investigate the behavior of liquid N2 jets having an initial temperature less than the critical temperature of N2, into ambient N2 at greater than the critical temperature, at various pressures ranging from less than to greater than the critical pressure. Two-dimensional Raman scattering is used as a diagnostic tool. The injector was a straight tube with a length-to diameter ratio of 100. The optical setup used a pulsed frequency-doubled Nd:Yag laser at 532 nm as an incident beam. Two-dimensional images were taken near the injector and results were interpreted in terms of density plots. At subcritical ambient pressures, a strong Raman signal was obtained and only a small number of images were needed for averaging. Substantial reduction of this signal was observed at supercritical pressures due to jet radial growth and mixing. The radial profiles of the intensity- surplus exhibited self-similar behavior at all the conditions tested. These profiles were shown to have been broadened by the interaction of the laser sheet and the jet interface. At pressures near and above the critical pressure, the modified profiles tended to assume the self similarity profile of gaseous turbulent jets. The initial growth rate of the jet as judged by the Raman signature also showed such a tendency towards gaseous turbulent jets. However, the differences in growth rates remained quite distinct, being nearly half the growth rate reported for gaseous jets. The initial growth rate was in reasonably good agreement with our earlier measurements using shadowgraphy if twice the FWHM of the normalized intensity plots was used.
