NONINTRUSIVE MEASUREMENTS FOR HIGH-SPEED, SUPERSONIC, AND HYPERSONIC FLOWS

The need to develop new diagnostics for turbulent flows at supersonic and hypersonic regimes is discussed. New experimental results can be o btained in supersonic flows by using the collective light scattering m ethod. Typical results obtained by this method in a supersonic mixing layer are illustrated. The collective light scattering method is a dir ectional densitometer (with a new type of spectral analysis of density fluctuations), a nonparticle anemometer, a Machmeter (or thermometer) , and a directional remote microphone. Various other optical technique s that can be applied for point, line-of-sight, or imaging measurement s are reviewed. For point measurements, light-scattering methods such as Raman, Rayleigh, or electron beam fluorescence are discussed, but o nly briefly, since they are of little use, especially when enthalpy is very high and flow naturally bright. Emphasis is placed instead on no nlinear laser spectroscopy such as coherent anti-Stokes Raman scatteri ng, which has recently been successful in determining temperature and density in high-enthalpy shocks. A description of diode laser absorpti on spectroscopy follows. A high data-rate instrument now routinely giv es the static temperature and the velocity of the stream in the hot sh ot facility F4 of ONERA, at stagnation enthalpies in excess of 15 MJ/k g. Finally, electron beam fluorescence imaging in the same facility ha s made it possible to perform measurements of velocity across the exte rnal boundary layer into the flow core using a high-energy-pulsed elec tron gun.