An optical density measuring system based on Rayleigh scattering was installed at an atmospheric wind tunnel. The system monitors the scattered light induced by a laser sheet irradiating the flowfleld behind a plane VKI-1 turbine cascade. Because of the scattering of air molecules, tracer particles are not required. The measuring procedure is based on a relative measurement and needs no calibration except consideration of the incident laser light energy. The system allows quantitative recording of the two-dimensional density field in a very short time. The density distributions behind the VKI-1 cascade are presented as experimental results for subsonic and transonic flow. The experimental data are compared with the results of a two-dimensional Navier-Stokes calculation. The results indicate that the measurement of the whole three-dimensional flowfleld in and behind cascades is possible if the experimental arrangement is adjusted.
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Fiedler et al. (1997) studied this question.
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