Diffusional-thermal instability in strained diffusion flames with unequal lewis numbers
- Diffusional-thermal instability in strained diffusion flames with unequal lewis numbers
- 김종수; 이수룡
- diffusional-thermal instability
- Issue Date
- Combustion theory and modelling
- VOL 3, NO 1, 123-146
- Nonlinear dynamics of diffusional-thermal instability in diffusion flames is numerically investigated by employing a diffusion flame established in the stagnant mixing layer as a model. Particular attention is focused on the pulsating-instability regime, which arises for Lewis numbers sufficiently greater than unity. Once the steady flame structure is obtained for a prescribed value of the initial Damko¨hler number, transient evolution of the flame is calculated after a finite amount of the Damko¨hler-number perturbation is imposed on the steady flame. Depending on whether the initial Damko¨hler number is greater than the bifurcation Damko¨hler number or not, evolution of the transient flame structures can be differently characterized. If the initial Damko¨hler number is smaller than the bifurcation Damko¨hler number, pulsating instability can be triggered without any external perturbations, while if the initial Damko¨hler number is greater than the bifurcation Damko¨hler number, flame oscillations can be amplified only for the perturbed Damko¨hler number smaller than the
threshold Damko¨hler number. Therefore, character of the nonlinear instability is subcritical. Once the oscillation amplitudes grow too large, flames are eventually led to extinction. Locus of the threshold Damko¨hler number is presented, which could be used as a revised extinction criterion for diffusion-flamelet library in the laminar flamelet regime of turbulent combustion.
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