Characterization of gaseous flows

Benefit description

This service capability allows the characterization of gaseous flows of molecular species, preferably inert (air, nitrogen, carbon dioxide ...). The flow fields to be characterized span those produced from micro-nozzles with various forms, as well as those produced around obstacles, both in subsonic and supersonic (Mach ~ 10) regimes, including shock waves. The characterization consists of the point-by-point mapping using the non-intrusive technique of inelastic light scattering (Raman spectroscopy). The primary quantities that can be mapped are the absolute number density (and composition in case of mixtures), and the rotational temperature; in favorable cases, the formation of condensed phases can also be detected. The laboratory has two complete instruments, each consisting of: 1) an installation for the production of gaseous micro-flows, and 2) a diagnostic system by Raman spectroscopy. The gas flows are produced in an expansion chamber, continuously evacuated by a set of high throughput (up to 20 mbar·liter/s) vacuum pumps (turbomolecular, roots-blower, and rotary); the nozzle and optics are placed inside the chamber, mounted on motorized micro-positioners operated by remote control. The diagnostic systems by Raman spectroscopy are formed by a high power (10 W) cw laser in the visible, and a dispersive spectrometer with a high sensitivity CCD detector cooled by liquid nitrogen. Some typical dimensions of the possible experiments are: - nozzle diameters from 0.05 mm to 1 mm; - size of the flow field, ~ 1 cm; - spatial resolution ~ 15 microns.