Hybrid LES/RANS Simulation of a Premixed Ethylene-Fueled Dual-Mode Scramjet Combustor: Small Cavity Configuration

摘要

Hydrocarbon fuels offer optimal high energy per volume for scramjet applications for sustained hypersonic flight but require additional residence time due to slower ignition delays (compared to hydrogen fuel). The injection of ethylene at the start of the isolator of a dual-mode scramjet combustor, operating in ramjet mode, allows sufficient mixing to achieve efficient, fully premixed, turbulent, hydrocarbon combustion. A cavity flame holder anchors the flame, supplying sufficient radicals to sustain a stable flame in the high-speed environment. Prior experimental/computational work has investigated the characteristics of various configurations of one such combustor at the University of Virginia Supersonic Combustion Facility (UVASCF) using coherent anti-Stokes Raman spectroscopy (CARS), particle image velocimetry (PIV), planar laser-induced fluorescence (PLIF) diagnostics, and hybrid large eddy simulation (LES) / Reynolds-averaged Navier-Stokes (RANS) modeling of combustor dynamics. This work investigates a new configuration with a smaller cavity extended into the center of the combustor with a strut and insert. The cavity is reduced in size to enable eventual direct numerical simulations (DNS) of the flame stabilization process. This work, however, focuses on modeling the full isolator / combustor geometry using a hybrid LES/RANS simulation strategy. PIV and PLIF diagnostics are compared with the simulations to analyze and characterize the conditions within the combustor, including flame structure, velocities, and pressure. The simulation results are analyzed to explain the influence of the shock train positioning on turbulence levels throughout the combustor and on the turbulent flame speed. The simulations show good agreement with the experimental data and with premixed turbulent combustion theory.