Physics – Fluid Dynamics
Scientific paper
2012-03-05
Physics
Fluid Dynamics
Scientific paper
In this paper we clarify the role of the Markstein Number (Mk) on the turbulent flame speed and its scaling, from experimental measurements on constant-pressure expanding turbulent flames. Turbulent flame speed data are presented for methane, ethylene and n-butane-air premixed flames with negative and positive Mk, propagating in nearly homogenous isotropic turbulence in a dual-chamber, fan-stirred vessel. The cold flow is characterized by high-speed particle image velocimetry, while the flame propagation rate is obtained by tracking high-speed Schlieren images. For all fuel-air mixtures of C1-C4 hydrocarbons presented in this work, the normalized turbulent flame speed data follows the recent theoretical [Chaudhuri, Akkerman and Law, Physical Review E, 84, (2011) 026322] and experimental [Chaudhuri, Wu, Zhu and Law, Physical Review Letters, 108, (2012), 044503], [Re_{T,f}]^{0.5} scaling, where the average radius is the length scale and thermal diffusivity is the transport property. For a constant Re_{T,f} it is experimentally observed that the normalized turbulent flame speed decreases with increasing Mk. Such an observation could be explained as a cumulative effect of flame curvatures controlled by Mk, from the largest to the smallest scales i.e. from the mean flame radius to the flame thickness with the smaller scales dominating due to their inherent large curvatures. Recent theoretical results qualitatively predict and explain such an observation as well.
Chaudhuri Swetaprovo
Law Chung K.
Wu Fujia
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