Kiselev S.P.   Kiselev V.P.   Zaikovskii V.N.  

The visualization method and numerical simulation using in the study of self - oscillations in a radial supersonuc overexpanded jet

Reporter: Kiselev S.P.

    The paper presents the results of experimental and theoretical studies of oscillations in a supersonic jet overexpanded arising from the radial nozzle. Optical imaging was performed expiration of a supersonic jet from a flat radial nozzle submerged space (air) with an exposure of 1 ms. It has been shown that the jet expands sharply at a certain distance from the nozzle. Videography expiration process with an exposure of about 4 ms showed that the dramatic expansion of the jet associated with the development of instability in the jet. The developing the jet bending oscillations of the jet lead to the collapse of the jet. As a result of the collapse of large-scale jet pulsations occur, which further due to nonlinear effects are transformed into small-scale turbulent fluctuations.
    Numerical calculations performed in the SST k-omega turbulence model using the package FLUENT, showed that at a certain distance from the nozzle flowing jet becomes unstable. Spectral analysis showed the presence of pulsations calculated discrete tone at a frequency of 5 kHz for the experimental conditions. This testifies to the development of self-oscillations in flowing radial jet. Feedback is supported by acoustic oscillations propagating from the jet to the nozzle exit gas at rest surrounding the jet. Perturbation jets penetrate and cause periodic displacements of the separation point of the boundary layer in the nozzle and adjust the angle of oblique shock waves generated in the vicinity of the boundary layer separation. As a result, oblique shock waves having large perturbation of the flow, the supersonic jet are transported downstream. The calculation results are in good agreement with the experimental data.
    The authors thank I.N. Kavun and S.G. Kundasevu for its assistance with the experiments.
    This work was partially supported by the RFBR (№ 14-01-00352).

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