Numerical simulations of turbulent lifted jet diffusion flames in a vitiated coflow using the stochastic multiple mapping conditioning approach

Abstract

Lifted turbulent jet diffusion flames of H2/N2 issued into a hot coflowing stream of combustion products from a lean premixed H2/air mixture are simulated using the stochastic multiple mapping conditioning (MMC) approach within the Reynolds-averaged Navier–Stokes (RANS) framework. The underlying turbulent flow is modeled using the two-equation k–ɛ model with modified constants. In the MMC approach, large-scale turbulent fluctuations are emulated by introducing suitable reference variables. A single reference variable is used here to describe the evolution of mixture fraction via a mapping function. The modified Curl's model has been adapted to model the micro-mixing term. A detailed chemical kinetic mechanism involving 9 species and 21 reversible reactions is used for H2/O2 combustion. The computed results from the present simulations are found to be in excellent agreement with the available experimental data. Numerical results are found to be sensitive to change in the minor dissipation timescale, which certainly controls the conditional fluctuations around the conditional mean. Also, the predicted flame lift-off heights obtained using the minor mixing time constant Cmin = 0.25 are found to be in close proximity with the experimentally observed values for the entire range of coflow temperatures.