Local statistics in a premixed turbulent Bunsen flame

Abstract

Turbulent combustion is critical in aviation industry due to its omnipresence in aircraft and rocket engines. Overall dynamics of turbulent flame is controlled by the local interactions between the flamefront and turbulence, and their influence on each other. To investigate such complex dynamics, we present an experimental investigation of a premixed Bunsen burner. First, the burner was characterized by evaluating the flow-field and turbulence properties using high-speed particle image velocimetry (HS-PIV). Next, we measured the flow field adjacent to the flame and compared it with the cold flow. We find that, there is reduction in turbulence strength when the flame is present, and the degree of reduction was found to be dependent on the Karlovitz number (defined as the ratio of flame time scale and turbulence time scale). Subsequently, we performed statistical analyses of local values of various stretch rates. We found that, with increasing Karlovitz number, the variance of stretch rates increase. Furthermore, our analysis showed that the three components of flame stretch rate are pairwise linked, which dictates the possible boundaries in joint probability distribution functions. Next, to understand the local evolution of the flamefront and its properties, we adopted a Lagrangian approach of studying ''flame particles''. By analyzing the instantaneous location of these flame particles, and examining the temporal evolution of local stretch rates, we have shown some key behavior of premixed turbulent flames.