Dependence of the Bluff Body Wake Structure on Flame Temperature Ratio

摘要

This paper describes an experimental investigation of the wake and flame characteristics of a bluff body stabilized flame. Prior investigations have clearly shown that the wake structure is markedly different at "high" and "low" flame density ratios. This paper describes a systematic analysis of the dependence of the flow field characteristics and flame sheet dynamics upon flame density ratio, pa/pb, over the range 1.7< pa/pb <3.4. This paper shows that two fundamentally different flame/flow behaviors are observed - characterized here as Kelvin-Helmholtz and Von-Karman vortex street dominated - at high and low pa/pb values, respectively. These are interpreted here as a transition from a convectively to absolutely unstable flow. This transition manifests itself in several ways with decreasing pa/pb values, including (1) the spectrum of the flame motion and flow field transitions from a distributed to a narrowband peak at St-0.24, and (2) the correlation between the two flame front branches monotonically increases. Finally, the intermittent nature of the flow field is emphasized, with the relative fraction of the two different flow/flame behaviors monotonically varying with pa/pb.