非流线体稳定的湍动预混火焰的吹灭动力学
This article concerns the flame dynamics of a bluff body stabilized turbulent premixed flame as itapproaches lean blowoff. Time resolved chemiluminescence imaging along with simultaneous particleimage velocimetry and OH planar laser-induced fluorescence were utilized in an axisymmetric bluff bodystabilized, propane-air flame to determine the sequence of events leading to blowoff and provide a quantitativeanalysis of the experimental results. It was found that as lean blowoff is approached by reductionof equivalence ratio, flame speed decreases and the flame shape progressively changes from a conical to acolumnar shape. For a stably burning conical flame away from blowoff, the flame front envelopes theshear layer vortices. Near blowoff, the columnar flame front and shear layer vortices overlap to inducehigh local stretch rates that exceed the extinction stretch rates instantaneously and in the mean, resultingin local flame extinction along the shear layers. Following shear layer extinction, fresh reactants can passthrough the shear layers to react within the recirculation zone with all other parts of the flame extinguished.This flame kernel within the recirculation zone may survive for a few milliseconds and can reignitethe shear layers such that the entire flame is reestablished for a short period. This extinction andreignition event can happen several times before final blowoff which occurs when the flame kernel failsto reignite the shear layers and ultimately leads to total flame extinguishment.