2ND-ORDER CONDITIONAL MOMENT CLOSURE FOR THE AUTOIGNITION OF TURBULENT FLOWS

The conditional moment closure with second-order approximation for the reaction rate and an equation for the conditional fluctuations of the temperature increments before autoignition of a turbulent nonpremixed flow has been developed for one-step chemistry. The explicit incorpor ation of conditional variances is necessitated due to the temperature fluctuations induced by heat losses from the reaction zone before igni tion, as indicated by recent direct numerical simulations (DNS). Predi cted ignition times and reaction zone structure are in very good agree ment with DNS data and the differences between the first- and second-o rder closure are discussed. (C) 1998 American Institute of Physics.