Local Strain Rate and Curvature Dependences of Scalar Dissipation Rate Transport in Turbulent Premixed Flames: A Direct Numerical Simulation Analysis

The statistical behaviours of the instantaneous scalar dissipation rate N-c. of reaction progress variable c in turbulent premixed flames have been analysed based on three-dimensional direct numerical simulation data of freely propagating statistically planar flame and V-flame configurations with different turbulent Reynolds number Re-t. The statistical behaviours of N-c. and different terms of its transport equation for planar and V-flames are found to be qualitatively similar. The mean contribution of the density-variation term T-1 is positive, whereas the molecular dissipation term (-D-2) acts as a leading order sink. The mean contribution of the strain rate term.. 2 is predominantly negative for the cases considered here. The mean reaction rate contribution T-3 is positive (negative) towards the unburned (burned) gas side of the flame, whereas the mean contribution of the diffusivity gradient term (D) assumes negative (positive) values towards the unburned (burned) gas side. The local statistical behaviours of N-c, T-1, T-2, T-3, (-D-2), and, f(D) have been analysed in terms of their marginal probability density functions (pdfs) and their joint pdfs with local tangential strain rate a(T) and curvature k(m). Detailed physical explanations have been provided for the observed behaviour.