Numerical simulation of a methane/air radiating turbulent diffusion flame

Reports numerical simulations of an unconfined methane‐air turbulent diffusion flame expanding from a porous burner. Turbulent combustion is simulated using the eddy dissipation concept (EDC) which supposes that the reaction rate is controlled by the turbulent structures which enhance the mixing of fuel and oxidant. Two statistical k‐e turbulence models have been tested: a standard high Reynolds number (HRN) and a more recent model based on the renormalization group theory (RNG). Radiation heat transfer and soot formation have been taken into account using P1‐approximation and transport submodels which reproduce the main phenomena encountered during soot production (nucleation, coagulation, surface growth). The set of coupled transport equations is solved numerically using a high order finite‐volume method, the velocity‐pressure coupling is treated by a projection technique. The numerical results confirm that 20‐25 percent of the combustion heat released is radiated away from the flame. Unsteady and unsymmetrical flame behaviour is observed for small Froude numbers which results from the development of Rayleigh‐Taylor like instabilities outside the flame surface. For higher Froude numbers the steady‐state and symmetrical nature of the solution is recovered.

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