Influences Of Gravity On Lean Premixed V-Flames Of Weak Turbulence

For the premixed flames of weak turbulence,the influence of turbulence and that of flame instability are comparable. Thus more influences,such as that of gravity,should be taken into consider when predicting or controlling these flames. The present study is focused on the influence of gravity on premixed V-flames of weak turbulence. The purpose is to provide basic data for the development of the theories about the premixed flames of weak turbulence.Methane-air premixed V-flames were detected under both normal gravity and microgravity by using drop tower facility and OH-PLIF. The dynamical behavior of flame fronts was recorded. To evaluate the influence of gravity,mean progressvariable c,flame surface density S and turbulent flame speed ST were extractedfrom the OH-PLIF images through image processing. The results show that wrinkles of the flames were enlarged and the values of ST were increased under microgravity.Also,the influence of gravity on flame wrinkles was weakened with the increase of turbulence intensity and the influence of gravity on ?was concentrated at the product side of flame brushes. For some of the flames,the influence of gravity was of the same order as that of turbulence or heal release. This implies that the influence of gravity should not be neglected in models of these flames. Rayleigh-Taylor mechanise anu baroclinic mechanism account for the suppression of flame wrinkles by gravity.To study the influence of gravity on flow field of the flames,numerical simulation was performed. The results show that buoyancy accelerated the rising plume of product and that the accelerated flow of the product in turn enhanced the rising flow near the burner exit. Also,the influence of gravity on flow field of the flames was weakened with increasing momentum of the coming flow,but no apparent correlation was found between the influence of gravity and heat release. The reason is that heat release also increased inertia force of product besides increasing buoyancy and these two effects were opposite to each other.As a whole,the influences of gravity on premixed flames are exhibited as two different effects:interface effect,namely the influence on flame fronts,and bulky effect,namely the influence on flow field,and the two effects couple with each other. Both of the two effects account for the change of overall features,such as flame angles,of the flames under microgravity.