  A study of a reacting boundary layer flow with heat transfer at conditions
typical for configurations at elevated pressures has been performed using a set
of direct numerical simulations. Effects of wall temperatures are investigated,
representative for cooled walls of gas turbines and sub-scale rocket engines
operating with hydrocarbon as fuels. The results show that exothermic chemical
reactions induced by the low-enthalpy in the boundary layer take place
predominantly in the logarthimic sub-layer. The majority of the heat release is
attributed 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 up
to 20% compared to the inert flow. The gas composition experiences strong
deviations from the chemical equilibrium conditions. In fact, a quenching of
the major species is observed within the viscous sub-layer and the transition
region. Analysis of chemical time-scales shows that the location of quenched
composition coincides with the region where the Damkoehler number decreases
below unity. Within the viscous sub-layer, a secondary reaction zone is
detected, involving the production of formyl and formaldehyde radicals that
provide an additional source of energy release. The analysis of the reaction
paths showed that reactions with zero activation energy are responsible for
this change in gas composition, which also account for the initial branching of
hydrocarbon fuels decomposition according to previous auto-ignition studies.
The effect of the secondary recombination reactions is more prominent for the
lower wall temperature case. Finally, the role of turbulent fluctuations on the
species net chemical production rates is evaluated, showing a strong
correlation between species and temperature fluctuations.
