A numerical study of a laser-induced plasma ignition system in a scramjet-like geometry is conducted. Simulations are based on experiments in which hydrogen is injected into a hypersonic air-crossflow, compressed by a ramp from a freestream Mach number of 8 to below hydrogen autoignition conditions. Ignition of the jet is attempted using a laser pulse, modeled in the simulations as a small region of high temperature and pressure corresponding to the energy input measured in the experiments. To capture the highly unsteady nature of the fuel-air interface and its coupling with the dynamics of the expanding laser spark, wall-modeled large-eddy Simulations are used to resolve the majority of turbulent motion. Thermal nonequilibrium and detailed finite-rate chemistry models are included in the calculations. The simulations indicate that the cloud of hydroxyl radicals detected in the experiments is created on the jet’s forward surface, as the expanding plasma kernel drives a blast wave into the bowshock surrounding the jet. This event raises the temperature and pressure in the upstream mixing layer, causing spontaneous ignition of the mixture. Within tens of microseconds the laser-induced combustion detaches from the jet and combustion ceases due to unfavorable conditions for flame anchoring in this area. Downstream of the jet, the simulations suggest that the plasma kernel remains can initiate radical formation in the wake region, but no stable flame forms due to nominally low pressures in the experimental condition studied.
Simulation of Laser-Induced Plasma Ignition in a Hypersonic Crossflow
AIAA Journal ; 56 , 8 ; 3047-3059
2018-08-01
Conference paper , Article (Journal)
Electronic Resource
English
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