Measurements of flame-vortex interaction dynamics and chemistry

An experimental study of the time-evolving dynamics and chemistry of a premixed, laminar flame interacting with a counter-propagating toroidal vortex has been performed. Dynamics were quantified using planar Particle Image Velocimetry (PIV) diagnostics to obtain velocity field images at selected times during the interaction. Each image consists of approximately 10,000 velocity vectors measured in both products and reactants. Measurements were performed on a regular grid with 590 {dollar}mu{dollar}m node spacing; the high spatial resolution and data density enable the calculation of instantaneous vorticity and dilatation rate fields, as well as local flame stretch rates. Vortices of three different strengths were interacted with the lean, propane-air flame to investigate flame wrinkling, pocket formation, and local extinction processes.; Generation and attenuation of vorticity by the freely-propagating flame are observed, and mechanisms are discussed by which this vorticity is produced and can affect flame propagation. A scaling analysis is presented so that such effects can be accounted for in turbulent combustion models.; Peaks in the dilatation rate field occur in the preheat zone of the flame, and these peak values are used as indicators of local flame strength. Results show not only reduced flame strength where positive stretch rates are large, but also 160% increases in flame strength in regions of strong negative stretch. Unsteady effects in flame response are found to be important.; Previous experiments during a similar interaction (lean methane-air flame) quantified OH-radical fluorescence using Planar Laser-Induced Fluorescence (PLIF) diagnostics, and velocity fields using two-color PIV. Instantaneous flame stretch rates are calculated from the velocity measurements, and data reduction factors relating OH fluorescence intensity to OH mole fraction are employed to compare measured profiles of OH to those previously computed for a Steady, Planar Counterflow Flame (SPCF) of the same mixture. Such comparisons enable assessment of the errors made by neglecting unsteadiness and time history effects in flamelet models of turbulent combustion. Unsteady stretch is found to affect the peak OH level and the thickness of the OH layer within the flame, producing typically 25% differences between measured and computed values. Heat losses are found to be important for the numerical prediction of extinction stretch rates.