Experimental investigation of the turbulence-flame interaction by using Lagrangian Coherent Structures

Chaos and its relation to turbulence play an important role in an investigation of the interaction of turbulence and flame. Lyapunov exponents (LEs) as a vital parameter for estimation of chaos can quantify the exponential divergence of initially close state-space trajectories. In this study, a highspeed (20-kHz) planar laser-induced fluorescence (PLIF) imaging of formaldehyde (CH2O) in a turbulent non-premixed CH4/H2 based turbulent flame together with velocity measurement using Particle Image Velocimetry (PIV) has been done. The Reynolds number of the jet based on the diameter of jet exit was varied within 12000-26000. A pulse-burst laser system was used to generate 355 nm laser pulses. The particles for PIV were illuminated with two diode-pumped Nd:YLF lasers frequency-doubled to 527 nm. Lagrangian coherent structures were used for obtaining flame topologies and tracking features through space and time and it is compared with the formaldehyde PLIF measurement. It is shown that the LEs map provides consistent evidence of the heat-release region and in turn represents the interaction of topological structures approaching to heat release region. Identification of LEs will also help for the understanding of the perturbation development and its interaction with flame.