Visualization of coherent structures in turbulent subsonic jet using planar laser induced fluorescence of acetone

¹ Optoelectronics Laboratory, Department of Physics, National Institute of Technology, Karnataka Surathkal, Mangalore 575 025, India
² Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore 560 012, India
³ Department of Aerospace Engineering, Indian Institute of Science, Bangalore 560 012, India

^a e-mail: vikasms2007@gmail.com

Received: 9 November 2012
Revised: 22 March 2013
Accepted: 16 April 2013
Published online: 11 June 2013

Abstract

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.