PLANAR AIR DENSITY-MEASUREMENTS NEAR MODEL SURFACES BY ULTRAVIOLET RAYLEIGH RAMAN-SCATTERING

The feasibility of planar ultraviolet laser-induced Rayleigh and Raman scattering for measurements of small air density variations near mode l wing surfaces is tested for applications in wind tunnels. Variations in air density of less than 1% are measured quantitatively by Rayleig h scattering in a plane of 3 X 6 cm2 in about 1 s under the extreme co ndition in which the laser directly irradiates the metal surface of th e wing. Raman scattering was tested as well because it is much less af fected by surface and Mie scattering. Therefore, it can be used for de nsity measurements much doser to the model surface and under the prese nce of dust and droplets with a precision of at least 2%. Further impr ovements of the measurement precision are possible and will be discuss ed.