Unsteady flamelet modelling of turbulent non-premixed combustion

In this study, RANS based axisymmetric simulations of the jet flames, bluffbody flames and swirling flames have been attempted by employing steady and unsteady flamelet models. The jet flames have been studied for pure hydrogen and diluted hydrogen (CO/H2/N2) fuels. The bluff-body flames have been studied for three different fuels CH4/H2, H2/CO and CH3OH. The swirling flame has been investigated for CH4/H2 fuel. The importance of unsteady effects is thoroughly assessed for combustion predictions. The transient effects are considered in a post-processing manner employing the Lagrangian Flamelet Model (LFM) for jet flames and the Eulerian Particle Flamelet Model (EPFM) for recirculating bluff-body and swirling flames. The LFM is valid for parabolic flows and uses Lagrangian residence time to calculate transient flamelets. The EPFM can be applied to both parabolic and elliptical flows. In the EPFM, the transient history of scalar dissipation rate, conditioned at stoichiometric mixture fraction is required to generate unsteady flamelets and obtained by tracing Eulerian particles. The probability density of particles is obtained by solving a passive scalar transport equation for each particle.