Development of high-resolution N-2 coherent anti-Stokes Raman scattering for measuring pressure, temperature, and density in high-speed gas flows

Mean and instantaneous measurements of pressure, temperature, and density h ave been acquired in an optically accessible gas cell and in the flow field of an underexpanded sonic jet by use of the high-resolution N-2 coherent a nti-Stokes Raman scattering (CARS) technique. This nonintrusive method reso lves the pressue- and temperature-sensitive rotational transitions of the n u = 0 --> 1 N-2 Q-branch to within Delta omega = 0.10 cm(-1). To extract th ermodynamic information from the experimental spectra, theoretical spectra, generated by a N-2 spectral modeling program, are fit to the experimental spectra in a least-squares manner. In the gas cell, the CARS-measured press ures compare favorably with transducer-measured pressures. The precision an d accuracy of the single-shot CARS pressure measurements increase at subatm ospheric conditions. Along the centerline of the underexpanded jet, the agr eement between the mean CARS P/T/rho measurements and similar quantities ex tracted from a Reynolds-averaged Navier-Stokes computational fluid dynamic simulation is generally excellent. This CARS technique is able to capture t he low-pressure and low-temperature conditions of the M = 3.4 flow entering the Mach disk, as well as the subsonic conditions immediately downstream o f this normal shock. (C) 2000 Optical Society of America OCIS codes: 280.24 90, 300.6450, 300.6420.