WIT Press

Numerical Simulations Of Variable Density Starting Jets


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WIT Press


S. Benteboula & G. Lauriat


Numerical simulations of variable density starting jets S. Benteboula1,2 & G. Lauriat3 1UPMC Univ Paris 06, UMR 7598, Laboratoire Jacques-Louis Lions F-75005, Paris, France 2CEA Saclay, DM2S/SFME/LTMF, 91191 Gif sur Yvette Cedex, France 3Universit´e Paris-Est, Laboratoire de Mod´elisation et Simulation Multi´echelle FRE 3160 CNRS, 77454 Marne-la-Vallee, France Abstract This work aims at developing computing tools for the numerical simulation of impulsively started jets with variable physical properties due to large thermal gradients. The fluid is injected at temperature Tj and density ρj in a quiescent surroundings at different temperature and density Ta, ρa. The 3D-time dependent Navier–Stokes equations, formulated in the low Mach number approximation, were numerically integrated by using a non divergence-free projection method. The computations were performed for 3D and axisymmetric jets, and for a wide range of the jet-to-ambient density ratio, α = ρj /ρa, providing the expected flow features. Except the formation of a leading vortex in the head of the flow followed by a jet stem, the results show that the behaviour and the dynamics are quite different for hot and cold jets. The hot jet is indeed characterised by a leading vortex in which the hotter fluid is concentrated, while the vortex ring is a region of intermediate temperature and density for a cold jet. Particular attention is given to the influence of α on the integral characteristics of vortex rings such as circulation and impulse. Keywords: numerical simulation, anisothermal vortex ring, low mach number flow, variable density. 1 Introduction The fluid injection through an orifice or a nozzle in a stagnant atmosphere leads to the generation of a vortex ring followed by a tail. Vortex rings are encountered


numerical simulation, anisothermal vortex ring, low mach number flow, variable density.