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A study of a reacting boundary layer flow with heat transfer at conditionstypical for configurations at elevated pressures has been performed using a setof direct numerical simulations. Effects of wall temperatures are investigated,representative for cooled walls of gas turbines and sub-scale rocket enginesoperating with hydrocarbon as fuels. The results show that exothermic chemicalreactions induced by the low-enthalpy in the boundary layer take placepredominantly in the logarthimic sub-layer. The majority of the heat release isattributed to the exothermic recombination of OH and CO to produce CO2 and H2O.The recombination reactions result in an increase of the wall heat loads by upto 20% compared to the inert flow. The gas composition experiences strongdeviations from the chemical equilibrium conditions. In fact, a quenching ofthe major species is observed within the viscous sub-layer and the transitionregion. Analysis of chemical time-scales shows that the location of quenchedcomposition coincides with the region where the Damkoehler number decreasesbelow unity. Within the viscous sub-layer, a secondary reaction zone isdetected, involving the production of formyl and formaldehyde radicals thatprovide an additional source of energy release. The analysis of the reactionpaths showed that reactions with zero activation energy are responsible forthis change in gas composition, which also account for the initial branching ofhydrocarbon fuels decomposition according to previous auto-ignition studies.The effect of the secondary recombination reactions is more prominent for thelower wall temperature case. Finally, the role of turbulent fluctuations on thespecies net chemical production rates is evaluated, showing a strongcorrelation between species and temperature fluctuations.

Heat transfer augmentation by recombination reactions in turbulent reacting boundary layers at elevated pressures