EFFECT OF CHEMICAL-REACTIONS ON DECAYING ISOTROPIC TURBULENCE

There have been many studies of turbulent combustion flows, however th e interaction between turbulent motion and the chemical reactions that occur in hypersonic hows has not been studied. Ln these flows, the ra te of product formation depends almost exclusively on the temperature, and small temperature fluctuations may produce large changes in the r ate of product formation. To study this process, we perform direct num erical simulations of reacting isotropic turbulence decay under condit ions typical of a hypersonic turbulent boundary layer flow. We find th at there is a positive feedback between the turbulence and exothermic reactions. That is, positive temperature fluctuations increase the rea ction rate, thereby increasing the heat released by the reaction, whic h further increases the temperature. Simultaneously, the pressure incr eases causing localized expansions and compressions that feed the turb ulent kinetic energy. The Reynolds stress budget shows that the feedba ck occurs through the pressure-strain term. We also find that the stre ngth of the feedback depends on how much heat is released, the rate at which it is released, and the turbulent Mach number. The feedback pro cess is negative for endothermic reactions, and temperature fluctuatio ns are damped. (C) 1998 American Institute of Physics.