Velocity and scalar statistics for premixed turbulent stagnation flames using PIV

Particle Image Velocimetry (PTV) has been used to study premixed turbulent methane-air flames in a stagnation plate configuration. The PIV images were recorded with a CCD video camera, and velocities have been calculated by cross-correlation. The flow was seeded with alumina particles so that velocities could be measured in both reactants and products, and a masking technique was used to improve results for interrogation spots located along the flame front. Contours of the instantaneous thin flame front have also been obtained from die PIV images, using the Light Sheet Tomography (LST) method based on the local intensity of Mie scattering from the seed particles. AU flames were within the wrinkled laminar flamelet regime, so the reaction progress variable c was assumed to be 0 in reactant gases and 1 in product gases, and intermediate values were not considered. Statistics of velocity and reaction progress variable, including Favre mean velocities <(u(i))over tilde>, Favre mean progress variable (c) over tilde, velocity intensities <(u(i)"(2))over tilde>, and turbulent fluxes of reaction progress variable <(u(i)" c ")over tilde>, have been obtained directly from the PIV data using ensemble averages. Favre mean radial velocities are shown to vary linearly with the radial coordinate, and Favre mean axial and radial velocities agree reasonably well with the theory of Bray et al. [1]. Evidence of countergradient diffusion is presented, and it is demons;rated that most of the axial velocity fluctuations in the flame brush are due to intermittency, although these fluctuations should not be considered turbulence.