Abstracts

Novosibirsk participants

The laminar-turbulent transition of a boundary layer represents complex process of disturbances excitation of a different type, their development, interaction with each other and mean flow, that lead to a turbulent condition. Usually this process at small intensity of exterior disturbances is conditionally parted on three basic stages: 1) generation of waves of instability in a boundary layer, for example of Tollmien-Schlichting (TS) waves (problem of a receptivity); 2) their amplification according to a linear stability theory; 3) non-linear stage of development and interaction of disturbances with the subsequent destruction of a laminar flow in turbulent. As to researches of excitation of waves of instability in a boundary layer by exterior disturbances, for a case of supersonic velocities it is the least investigated stage of process of origin of turbulence. The creation of a controlled disturbances source in ITAM SB RAS has allowed to initiate with experimental study of a supersonic boundary layer receptivity. The measurements were performed in a supersonic low noise wind tunnel Т-325 of the Institute of Theoretical and Applied Mechanics of the Russian Academy of Sciences with the test section dimensions 600*200*200 mm at Mach number М=2 and 3.5. The model consists of two plates, established under a zero angle of attack. A generator of periodic disturbances, based on electrical discharge, was mounted on the plate 1. As a result of the electric discharge, initiated at frequency f, the disturbances appeared in the boundary layer and propagated downstream. This process was accompanied by the sound radiation into the free stream. Three reference zones of radiation are chosen. More precisely this radiation was used as external controlled disturbances. Disturbances in free stream and in the boundary layer of plate 2 were registered by the hot-wire anemometer. In experiments the fell on the leading edge of the plate 2 from below. In this case generation of disturbances in the boundary layer by the external controlled acoustic field takes place only in a vicinity of leading edge of the plate 2. The leading edge of a plate was irradiated by the controllable disturbances from below in relation to the excited boundary layer. In this case generation of disturbances in the boundary layer by the external controlled acoustic field takes place only in a vicinity of leading edge of the plate 2. In this case it was possible to carry out quantitative comparison of levels of initial acoustic disturbances in the free stream and eigen fluctuations of the supersonic boundary layer caused by them. Factors of transformation of acoustic disturbances into the eigen fluctuations of the supersonic boundary layer were obtained for the first time from the ratio of the amplitude of disturbances generated in the boundary layer to the amplitude of acoustic waves falling onto the sharp or blunted leading edge. Influence of Mach number of flow was considered. It was found, that the excitation of disturbances in the boundary layer by external disturbances at the sharp leading edge grow with Mach number increasing and the transformation coefficients for the oblique waves in the boundary layer are more, than for the plane wave at b"0. Is shown, that the excitation of disturbances in a boundary layer by exterior disturbances happens considerably more intensively for the case of blunted leading edge, than for the case of sharp leading edge. This research has been supported by Russian Fundamental Research Foundation, grant 99-01-00623.

Note. Abstracts are published in author's edition

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