Numerical study of hydrogen–air mixing in turbulent compressible coaxial jets

Abstract

Numerical simulations are carried out to study the space development of hydrogen–Air mixing jets discharging in to a confined environment. The full Navier-Stokes equations are solved with a high order Godunov's scheme piecewise parabolic method (PPM) with the approximate Riemann solver of Roe. The case considered in this study is based on the experimental work of Eggers (1971). A great attention has been paid to the computation of the dynamic and mixture field, in order to analyse deeply by means of flow visualizations and statistics the characteristics phenomena of the turbulent mixing. Hydrogen species is seeded in the inner jet and the air in the supersonic co-flow. The aim is to comprehend the turbulent structures effect on the mixing process of hydrogen and air. The approach is mainly based on Monotone Integrated Large Eddy Simulations (MILES). The study shows the MILES ability to track mixing process in such configuration as the grid resolution is important.Furthermore, it is found that the turbulent mixing activity is subjected to an intermittent specificity of the coherent vortices: ring structures with intermittent mushroom-type structures characterizing the ejection phenomena due to the longitudinal counter-rotating vortices. The H2 is quasi-completely dissipated as it is entrained outward the rings and transported by the irrotational stream (air). To overcome this situation, it is recommended to lock the inner jet by an outer jet. The studies with and without confinement display the same results even in 2D as the convective Mach number is subsonic Mc=0.44.