Faculty Publications
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Item Quantitative density imaging of subsonic jet using planar laser induced fluorescence of MEK(2012) Shelar, M.S.; Umesh, G.; Hegde, G.M.; Jagadeesh, G.; Reddy, K.P.J.Quantitative molecular density distribution of Methyl ethyl ketone (MEK) in turbulent nitrogen jet (Re≈2-3×103) was measured using PLIF technique. The tracer (MEK) was seeded in the nitrogen jet by purging through the liquid MEK at ambient temperature. Planar laser sheet from frequency quadrupled, Q-switched, Nd: YAG laser (266 nm) was used as an excitation source. Emitted fluorescence images of jet flow field were recorded on CMOS camera. To obtain quantitative density profile, the dependence of PLIF intensity on MEK partial pressure was employed. Thus an instantaneous quantitative density image of nitrogen jet, seeded with MEK was obtained. © 2012 IEEE.Item Visualization of coherent structures in turbulent subsonic jet using planar laser induced fluorescence of acetone(2013) Shelar, V.M.; Hegde, G.M.; Umesh, G.; Jagadeesh, G.; Reddy, K.P.J.In this paper, we present the molecular density distribution measurement in turbulent nitrogen jet (Re ? 3×103), using acetone as molecular tracer. The tracer was seeded in the nitrogen jet by purging through the liquid acetone at ambient temperature. Planar laser sheet of 266 nm wavelength from frequency quadrupled, Q-switched, Nd:YAG laser was used as an excitation source. Emitted fluorescence images of jet flow field were recorded on CMOS camera. The dependence of planar laser induced fluorescence (PLIF) intensity on acetone vapor density was used to convert PLIF image of nitrogen jet into the density image on pixel-by-pixel basis. Instantaneous quantitative density image of nitrogen jet, seeded with acetone, was obtained. The arrowhead-shaped coherent turbulent structures were observed in the present work. It was found that coherent structures were non-overlapping with separate boundaries. Breaking of coherent structures into turbulence was clearly observed above four times jet width. © EDP Sciences, 2013.Item Gas phase oxygen quenching studies of ketone tracers for laser-induced fluorescence applications in nitrogen bath gas(2014) Shelar, V.M.; Hegde, G.M.; Umesh, G.; Jagadeesh, G.; Reddy, K.P.J.In this paper we report the quantitative oxygen quenching effect on laser-induced fluorescence of acetone, methyl ethyl ketone, and 3-pentanone at low pressures (?700 torr) with oxygen partial pressures up to 450 torr. Nitrogen was used as a bath gas in which these molecular tracers were added in different quantities according to their vapor pressure at room temperature. These tracers were excited by using a frequency-quadrupled, Q-switched, Nd:YAG laser (266 nm). Stern-Volmer plots were found to be linear for all the tracers, suggesting that quenching is collisional in nature. Stern-Volmer coefficients (ksv) and quenching rate constants (kq) were calculated from Stern-Volmer plots. The effects of oxygen on the laser-induced fluorescence of acetone, methyl ethyl ketone, and 3-pentanone were compared with each other. Further, the Smoluchowski theory was used to calculate the quenching parameters and compared with the experimental results. Copyright © Taylor & Francis Group, LLC.Item Acetone planar laser-induced fluorescence for supersonic flow visualization in air and nitrogen jet(University of Malaya, 2014) Shelar, V.M.; Shrisha Rao, M.V.; Hegde, G.M.; Umesh, G.; Jagadeesh, G.; Reddy, P.J.Background: Laser based flow visualization techniques are indispensable tools for flow visualization in fluid dynamics and combustion diagnostics. Among these, PLIF is very popular because of its capability to give quantitative information about the flow. This paper reports the acetone tracer-based PLIF imaging of supersonic jet with air and nitrogen as bath gases. Methods: The tracer was seeded in the flow by purging bath gas through the liquid acetone at ambient temperature. Planar laser sheet from frequency quadrupled, Q-switched, Nd:YAG laser (266 nm) was used as an excitation source. Emitted PLIF images of a jet flow field were recorded on ICCD camera. Results: In this study, the dependence of PLIF images intensity on oxygen by comparing nitrogen jet with air in supersonic regime was presented. A lower temperature at the exit of the supersonic jet condenses the tracer which in turn forms droplets. Conclusions: There was a significant decrease in the PLIF image intensity in the case of air. This may be attributed to the oxygen present in the air. It is shown that image adding and Gaussian image processing of PLIF images for steadystate jet improve the quality of images. © 2014 Shelar et al.; licensee Springer.