LES MODELLING FOR FREE, INCOMPRESSIBLE AND NON-ISOTHERMAL ROUND JET

A circular, free, turbulent, incompressible and non-isothermal air jet is simulated by using a LES approach. The simulation is validated by comparing with experimental and numerical data taken from the literature the axial distributions of mean centreline axial velocity and temperature as well as radial profiles of mean velocity, mean temperature and of direct second order moments of velocity components. Subsequently, the jet behaviour related to its vortical structures is studied. In the first 5-6D downstream from the orifice, the presence of vortex rings affects the velocity and temperature fields. The spatiotemporal visualisation of the traces that vortex rings design on two parallel lines to the jet axis, permits to graphically compute their convection velocity, frequency of emergence, size and axial progression before breaking-up. These results are also supported by the spectral analysis carried out on a Boolean function (a spatiotemporal indicator of the presence of a vortex).