Nonintrusive pressure and temperature measurements in an underexpanded sonic jet flowfield

Nonintrusive pressure and temperature measurements are performed in the flowfield of an underexpanded sonic jet using high-resolution nitrogen coherent anti-Stokes Raman scattering (CARS). The jet is operated with a fully expanded jet Mach number of 1.83. The time-averaged CARS measurements start at the jet exit and are spatially well resolved, elucidating the near-field shock structure of the jet. For example, the location of the Mach disk is resolved to within 350 μm. Downstream of the Mach disk, viscous effects cause the slip line between the inner and outer jet regions to transition to an annular shear layer. The measurements also define the curved outer shear layer bounding the jet. The experimental pressure and temperature data are compared to similar quantities extracted from a Reynolds-averaged Navier-Stokes computational-fluid-dynamic (RANS CFD) simulation of the flowfleld. Except at the jet exit, the mean CARS measurements and CFD predictions along the centerline and along radial traverses in the jet flowfield are in good agreement. The low-pressure (12 kPa) and low-temperature (98 K) conditions of the Mach 3.3 flow entering the Mach disk, as well as the conditions (107 kPa, 262 K) immediately downstream of the disk, are well resolved. Slight deviations of the experimental mean pressure measurements from the CFD pressure distribution in the outer compressible shear layer suggest the existence of streamwise-oriented vortices. Comparisons between these data and measurements from other streamwise-vortex studies are presented.