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 model wing surfaces is tested for applications in wind tunnels. Variations in air density of less than 1% are measured quantitatively by Rayleigh scattering in a plane of 3 X 6 cm2 in about 1 s under the extreme condition in which the laser directly irradiates the metal surface of the wing. Raman scattering was tested as well because it is much less affected by surface and Mie scattering. Therefore, it can be used for density measurements much closer to the model surface and under the presence of dust and droplets with a precision of at least 2%. Further improvements of the measurement precision are possible and will be discussed.