Dual-pump coherent anti-stokes raman spectroscopy measurements in a dual-mode scramjet

In this paper, the authors describe dual-pump coherent anti-Stokes Raman spectroscopy (CARS) measurements of mixing and combustion in a direct-connect scramjet combustor operating at equivalent flight Mach typical of the ramjet-scramjet transition, in the scram mode. Measurements were performed in the University of Virginia's scramjet test facility in which the air is heated by electrical resistance heaters. The CARS technique is used to acquire temporally and spatially resolved measurements of temperature and species mole fraction. Measurements were at four planes: one upstream of an H₂ fuel injector and three downstream. Contour plots of mean flow and standard deviation statistics are presented for cases with and without reaction of the fuel. The vibrational temperature at the exit of the M = 2 facility nozzle, and in the freestream of the scramjet combustor, is elevated compared with the rotational temperature; the air-N₂ vibrational temperature is the same as the facility stagnation temperature. There are spatial nonuniformities of temperature exiting the heater. The mixing of the fuel jet from the single ramp wall injector and the growth of the plume downstream is shown. The flame is attached at the injector and propagates from the wall adjacent to the fuel plume, around the periphery of the plume, before engulfing the whole plume. Computational fluid dynamics modeling shows that the flow can be predicted well using hybrid large-eddy simulation/Reynolds-averaged Navier-Stokes methods with relatively simple subgrid models, provided facility effects are properly accounted for.