Chemical timescale analysis of the Partially Stirred Reactor model for a hydrogen-fuelled scramjet

Abstract

Scramjet engines offer a promising option for powering hypersonic vehicles, although the unique characteristics of supersonic combustion present numerous challenges. Notably, turbulence-chemistry interactions are significant in supersonic flows, demanding specific combustion formulations in numerical simulations due to their dissimilarity from traditional combustion systems. This work evaluates the performance of the Partially Stirred Reactor (PaSR) closure of the mean chemical source term by performing Reynolds-Averaged Navier-Stokes (RANS) simulations of the German Aerospace Centre (DLR) scramjet. The PaSR approach requires defining a chemical timescale, and this study assesses several formulations. Among them, the Fastest Formation Rate (FFR) does not provide stable combustion, while the Slowest Formation Rate (SFR) achieve fairly good predictions. Moreover, the sensitivity to species selection in calculating the chemical timescale is investigated, as well as the impact of two PaSR residence time formulations. A newly proposed Batchelor-based mixing timescale performs well with both the SFR and FFR formulations and guarantees a coupling between chemical and mixing times. It also accounts for species diffusivity, which can have important effects on hydrogen-based fuel combustion.

Keywords

• Supersonic combustion
• Hydrogen
• Scramjet
• Reynolds-averaged Navier-Stokes
• Partially Stirred Reactor
• Chemical timescales