| 1. |
- Borodulin, V. I., et al.
(författare)
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Excitation of 3D TS-waves in a swept-wing boundary layer by surface vibrations and freestream vortices
- 2018
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Ingår i: AIP Conference Proceedings. - : American Institute of Physics Inc.. - 0094-243X. - 9780735417472
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Konferensbidrag (refereegranskat)abstract
- There are several kinds of velocity disturbances, which may affect the transition to turbulence in a swept wing boundary layer. Tollmien-Schlichting (TS) waves are among most important of them. The properties of TS waves and their potential competition with cross-flow waves on a swept wing are poorly studied in theoretical works and were not studied experimentally at all. This paper presents the method of excitation of fully controlled 3D TS waves via interaction of free-stream vortices and surface vibrations. The experimental approach developed here will be used for investigation of the corresponding receptivity problem.
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| 2. |
- Borodulin, V. I., et al.
(författare)
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Quantitative study of localized mechanisms of excitation of cross-flow instability modes in a swept-wing boundary layer
- 2018
-
Ingår i: CONFERENCE OF YOUNG SCIENTISTS IN MECHANICS. - : IOP PUBLISHING LTD.
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Konferensbidrag (refereegranskat)abstract
- An experimental study of two efficient receptivity mechanisms of excitation of cross-flow (CF) instability modes is carried out in a boundary layer of a real airfoil section of a swept wing due to: (i) action of localized surface vibrations, and (ii) scattering of 2D freestream vortices on them. It is found that the two mechanisms lead to rather efficient excitation of CF-modes both at surface vibration frequency and at combination 'vortexvibration' frequencies. First estimations of the corresponding localized receptivity coefficients are obtained. Direct comparison of the experimental amplification curves of the excited CF-modes with those calculated based on the linear stability theory (LST) has shown that the experimental data obtained at vibration frequency are in excellent agreement with the LST. At the same time, growth rates of the CF-modes excited at combination frequencies are found to be completely inconsistent with the LST. A possible explanation of this phenomenon via action of a new efficient distributed receptivity mechanism is suggested. This mechanism is associated with scattering of freestream vortices on rather high-amplitude CF-modes excited by surface vibrations.
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| 3. |
- Kachanov, Y. S., et al.
(författare)
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Generation of unsteady CF-instability modes by vibrational and vibration-vortex localized receptivity mechanisms
- 2018
-
Ingår i: AIP Conference Proceedings. - : American Institute of Physics Inc.. - 0094-243X. - 9780735417472
-
Konferensbidrag (refereegranskat)abstract
- The paper is based on results obtained within an international project 'RECEPT' of the European Framework Program FP7. The experiments were carried out in a three-dimensional boundary layer developing on an experimental model of a long-laminar-run swept airfoil (sweep angle of 35°). The model was mounted in a test section of the low-turbulence wind-tunnel MTL (KTH, Stockholm) at an angle of attack of -5°and equipped with sidewalls provided satisfaction of infinite-span conditions. The cross-flow (CF) instability modes were predominant in this case, while the Tollmien-Schlichting (TS) waves were suppressed by a favorable pressure gradient. The main measurements were carried out by means of hot-wire anemometry at conditions of excitation of fully controlled, unsteady surface and flow perturbations. These perturbations were excited by special sources: (1) a row of oscillating membranes and (2) a vibrating cwire, at frequencies of f s and f v , respectively. A very good, quantitative agreement between the measured and calculated (by linear stability theory based on PSE approach) amplification curves was found at surface frequency f s . However, the evolution of the CF-modes excited at difference combination frequency f sv- = f s - f v turned out to be very much different from the theoretical one. Thorough analysis of the obtained results has shown that the only explanation of these discrepancies can be associated with presence of a distributed receptivity mechanism due to scattering of freestream vortices on the CF-instability waves excited by surface vibrations. Another unusual and unexpected phenomenon found in the present experiments is associated with anomalous amplification of difference combination modes with the zero spanwise wavenumbers β′. This phenomenon was observed in the flow, which is stable with respect to both CF- and TS-waves having β′ = 0 for all frequencies. There is no explanation of this finding at present.
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