Abstract
A numerical study on the characteristics of turbulent fluctuations in two-dimensional fuel jet diffusion flames developed in a co-flowing air stream is made by adopting the flame surface model of infinite chemical reaction rate and unit Lewis number. The time dependent Navier-Stokes equation with variable density is solved numerically by using a finite difference method. The temperature dependence of viscosity and diffusion coefficients is taken into account so as to study effects of decreased density and increased viscosity on the flow and flame fluctuations. The numerical calculation is done for the cases when methane is injected into a co-flowing air stream with Reynolds number 1000 and 2000. It is found that most of the induced transverse velocity fluctuations are always confined inside the instantaneous flame surface. The comparison of the flame surface behavior for five jet cases with different density and viscosity properties has shown that decreased density in the flame suppresses lateral expansion of the fluctuating flame surface, resulting in a narrower turbulent flame width. On the other hand, the increased viscosity is found to make the amplitude of the fluctuating flame surface smaller through the suppression of transverse velocity fluctuation.
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