Laser transillumination study of supersonic jets
D.A. Marakasov, A.A. Sukharev, R.Sh. Tsvyk
V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, Tomsk, Russia
Keywords: supersonic jet, fluctuations, spectrum, sensing laser beam, vortex
Abstract
A promising method for studying the flow structure in turbulent supersonic jets is the contactless method of laser transillumination. Interpretation of the experimental results is a non-trivial task, especially with respect to turbulence, due to the spatial inhomogeneity of the fields of gas-dynamic characteristics. In this article, the spectral composition of turbulence in axially symmetric jets in the root region (before the closure of the mixing layers) is analyzed based on laser sensing results. The results of experimental studies of intensity fluctuations of a laser beam propagating through a supersonic flooded jet are presented. The spectral fluctuation power density fully corresponds to the known experimental and calculated spectra for a moving turbulent medium, with the exception of the high-frequency interval. The spectrum in this interval is a superposition of two power components, one of which is close to the known value -14/3 and the other is smaller. It is shown that this is due to the difference in motion velocities and the structure of vortex flows in the outer and inner mixing layers. The results can be used in calculating gas-dynamic characteristics and acoustic radiation of jet engines.
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