The study of flame-vortex interactions using a particle image velocimeter

An experiment has been devised to examine the evolution of flame stretch, flame curvature and flow strain rate during the interaction of a premixed (lean, methane-air) laminar V-flame and a Karman Vortex Street. The experimental technique relies heavily upon the use of a particle image velocimeter both to make strain rate measurements and also to quantify vortex structure. Thirty flame realizations are studied at a single operating condition.;A sequence of events occurring during the interaction was constructed from flow visualization results and flame stretch measurements. A large region of positive flame curvature (convex to the reactants) bordered by cusps (small areas of large negative curvature) is formed by a pair of counter-rotating vortices that produces a local velocity deficit into which the flame propagates. The action of the flame tends to spread the pair apart while distorting and weakening individual vortices, thus signaling the end of the interaction.;Velocity, vorticity, flame stretch rate, flame curvature and flame strain rate plots are provided for several realizations. In addition, probability density functions (pdf) and scatter plots for these quantities are provided for the entire set of thirty flame realizations. Scatter plots indicate that the flame curvature and flow strain rate are found to be statistically independent, and that the average flame stretch rate for an individual flame is determined directly from the average flame curvature. Average flow strain is found to be nearly zero in accordance with the periodic flow pattern surrounding the vortex street.;Results further indicate that flame properties such as flame speed and temperature will not be significantly affected by flame stretch. This condition provides an ideal baseline comparison for additional PIV system measurements and is an excellent test case for numerical code development. Comparison between these results and the action of large scales in premixed turbulent combustion is also discussed. The action flow scales much larger than the flame thickness in a turbulent flame is inferred from the interaction of laminar vortices with a laminar flame front.