Numerical simulation of variable density subsonic turbulent jets by using the k-ε model

A numerical investigation is reported for round free turbulent non-isothermal binary mixing incompressible jets discharging into a quiescent atmosphere. The standard k-ε model is used. The standard closure schemes in Favre averaged variables are first introduced. The parabolic numerical simulation method of Patankar and Spalding [Heat and Mass Transfer in Boundary Layer, Intertext Books, London, 1970] is followed. The numerical simulations show a satisfactory agreement with the experimental results of Chassaing [Mélange turbulent de gaz inertes dans un jet de tube libre, Thèse d'état, INPT, 1979], Birch et al. [J. Fluid Mech. 88 (3) (1978) 431-449] and Panchapakesan et Lumley [J. Fluid Mech. 246 (1993) 197-223, 225-247]. The developed numerical code is used to study the sensitivity of turbulent characteristics to the density ratio between the jet and the ambient air. The decay rate of the mean axial velocity, temperature and mass fraction are shown to increase with decreasing density ratio. This confirms a higher mixing efficiency (parameter which determines the quantity of mass or heat injected at the jet exit and found further from the axis) when the density ratio between the jet and the quiescent air decreases. Finally, it is shown that the density effects are affected by the buoyancy terms in the similarity region of the jet.