  The present paper deals with the numerical study of high pressure LOx/H2 or
LOx/hydrocarbon combustion for propulsion systems. The present research effort
is driven by the continued interest in achieving low cost, reliable access to
space and more recently, by the renewed interest in hypersonic transportation
systems capable of reducing time-to-destination. Moreover, combustion at high
pressure has been assumed as a key issue to achieve better propulsive
performance and lower environmental impact, as long as the replacement of
hydrogen with a hydrocarbon, to reduce the costs related to ground operations
and increase flexibility. The current work provides a model for the numerical
simulation of high- pressure turbulent combustion employing detailed chemistry
description, embedded in a RANS equations solver with a Low Reynolds number
k-omega turbulence model. The model used to study such a combustion phenomenon
is an extension of the standard flamelet-progress-variable (FPV) turbulent
combustion model combined with a Reynolds Averaged Navier-Stokes equation
Solver (RANS). In the FPV model, all of the thermo-chemical quantities are
evaluated by evolving the mixture fraction Z and a progress variable C. When
using a turbulence model in conjunction with FPV model, a probability density
function (PDF) is required to evaluate statistical averages of chemical
quantities. The choice of such PDF must be a compromise between computational
costs and accuracy level. State- of-the-art FPV models are built presuming the
functional shape of the joint PDF of Z and C in order to evaluate
Favre-averages of thermodynamic quantities. The model here proposed evaluates
the most probable joint distribution of Z and C without any assumption on their
behavior.
