Vortex control in a spatially growing round jet

Abstract

Due to the diversity of their coherent structures, axisymmetric jets constitute a prototype of free shear flows of vital importance from both a fundamental as well as a more applied point of view. Indeed, a better understanding of the jet vortex structures should make possible the active control of the jet (spreading rate, mixing enhancement, …) for engineering applications (see e.g. Zaman et al. [25]). In the last five years, the progress in the experimental methods for detection and identification has made possible a detailed investigation of the complex three-dimensional coherent vortices imbedded within this flow. For instance, the influence of the entrainment of the secondary streamwise vortices has been studied by Liepmann and Gharib [11]. On the numerical side, several simulations of two-dimensional or temporally evolving jets have been performed. Very few have however investigated the three-dimensional spatial development of the round jet. We here present a statistical and topological numerical study of the spatial growth of the round jet from the nozzle up to sixteen diameters downstream. The use of large-eddy simulations (LES) techniques allow us to reach high values of the Reynolds number: here, Re is 25000. The advantage of these techniques is that high Reynolds number flows can be simulated with a moderate number of resolution points and a reasonable computer cost. Our goal here is to demonstrate the ability of the LES to properly reproduce the coherent vortex dynamics in the transitional region of the jet. We also show the possibility of controlling the jet behaviour by manipulating the inflow conditions. The detailed results are presented in Urbin (1997) [21], Urbin and Métais [22] and Urbin et al. [23].