Simulation of a Scramjet Combustor: A Priori Study of Thermochemistry Tabulation Techniques

Abstract

Large eddy simulations (LES) of a scramjet combustor are reported in this paper. The case under study is a cavity-based combustion chamber that is experimentally studied at the U.S Air Force Research Laboratory. The chamber is fed by eleven injectors. The computational domains are either simplified including only one or two injectors or complete with the 11 injectors. A good agreement is found between experimental data (velocities measured by PIV) and results from the LES if the kinetic used is chosen with care. A high temperature is found inside the cavity promoting a reactive zone located in the mixing layer where the flow velocity is high. At this location, the combustion occurs first in a diffusion dominated regime followed by the efficient burning of a well mixed mixture (rich then lean). A significant diffusion dominated burning is also found inside the cavity, mostly at the interface between the two recirculation zones. The simulation of the complete geometry revealed a transverse phenomenon on the temperature and mixing fields, but which had nevertheless little effect on the comparison with the available experimental data. A tabulation of the chemistry based on a premixed flamelet library without compressibility effects has been tested a priori on the results of the simulation with one injector. Good results on temperature and H 2 O fields are found. Significant localized discrepancies appeared on CO and CO 2 fields due to the complexity of the combustion regimes, while compressibility effects were found to be weak for the configuration studied.

Stabilisation and extinction mechanisms of flames in cavity flameholder scramjets

“…All these results are consistent with other literature articles for which RANS (Reynolds Average Navier-Stokes) [16] or different RANS-LES hybrid approaches [17] have been tested. Further comparisons were made on the velocity and wall pressure profiles for the MHF case and a good agreement was found by comparison with the experimental data [10,12].…”

“…A no-model assumption is used to compute the chemical source terms as in [8,18]. It has been verified in [10,12,31] that these assumptions do not modify the results and scenarios described hereafter. The use of the quasi-laminar-chemistry approach has been found acceptable in [5] for small scramjet-like problems.…”

“…It becomes then a formidable challenge to predict such behaviors and the use of numerical simulations appears as a necessary tool [5]. In particular, the use of Large-Eddy Simulation (LES) for supersonic combustion is now becoming relevant [6,7,8,9,10] even if for highspeed combustion, the choice of turbulent-combustion models can be challenging [11,12] since the majority of models in literature have been developed for low-speed combustion. Besides, combustion can occur near or in the distributed-reaction-like regime [5], i.e.…”