A numerical investigation of nonpremixed laminar, swirling, hydrogen-air jet flames

To better understand combustion stabilization in hydrogen-fueled gas turbines, numerical simulations using the spectral element-code Nek5000 are performed at moderate Reynolds numbers to characterize nonpremixed diffusion flames in axisymmetric configurations involving a swirling hydrogen jet discharging into a preheated coflow stream of air diluted with nitrogen. The conservation equations are formulated using the low Mach number approximation, with a mixture-averaged model employed to describe molecular transport. Fuel oxidation is described using both detailed chemistry and an explicit one-step reduced mechanism previously derived by assuming all chemical intermediates to maintain steady state, an approximation afforded by the high-pressure conditions existing in gas-turbine combustion chambers. The interplay of vortex breakdown with various flame behaviors, such as liftoff and blowoff, is characterized as a function of the jet-to-coflow velocity ratio, the swirl number and the Damkohler number. The results clearly demonstrate the predictive capability of the one-step chemistry in connection with the numerical computation of hydrogen combustion in high-pressure environments.