Development of the trailing shear layer in a starting jet during pinch-off
Yu, S. C. M.
Date of Issue2012
School of Mechanical and Aerospace Engineering
Experiments on a circular starting jet generated by a piston–cylinder arrangement, over a range of Reynolds number from to , are conducted so as to investigate the development of the trailing shear layer during the leading vortex ring formation, as well as the corresponding effects on the pinch-off process. Results obtained by digital particle image velocimetry (DPIV) show that secondary vortices start to develop in the trailing jet only after the critical time scale, the ‘formation number’, is achieved. The subsequent growth of the secondary vortices reduces the vorticity flux being fed into the leading vortex ring and, as a consequence, constrains the growth of leading vortex ring with larger circulation. Evolution of perturbation waves into secondary vortices is found to associate with growth and translation of the leading vortex ring during the formation process. A dimensionless parameter ‘’, defined as ), is therefore proposed to characterize the effect of the leading vortex ring on suppressing the nonlinear development of instability in the trailing shear layer, i.e. the initial roll-up of the secondary vortices. In a starting jet, follows a decreasing trend with the formation time . A critical value is identified experimentally, which physically coincides with the initiation of the first secondary vortex roll-up and, therefore, indicates the onset of pinch-off process.
Mechanical and Aerospace Engineering
Journal of fluid mechanics
© 2012 Cambridge University Press.This paper was published in Journal of Fluid Mechanics and is made available as an electronic reprint (preprint) with permission of Cambridge University Press. The paper can be found at the following official DOI: [http://dx.doi.org/10.1017/jfm.2012.138]. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper is prohibited and is subject to penalties under law.