| 1. |
- Borodulin, V. I., et al.
(författare)
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Receptivity coefficients of vortex-vibrational type at excitation of 3D Tollmien-Schlichting waves in a boundary layer on a swept wing
- 2019
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Ingår i: HIGH-ENERGY PROCESSES IN CONDENSED MATTER (HEPCM 2019): Proceedings of the XXVI Conference on High-Energy Processes in Condensed Matter, dedicated to the 150th anniversary of the birth of S.A. Chaplygin. - : American Institute of Physics (AIP). - 9780735418653
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Konferensbidrag (refereegranskat)abstract
- The paper is devoted to the first results of an experimental quantitative study of the receptivity mechanism of a swept-wing laminar boundary layer related to scattering of 2D freestream vortices (with frequency fv) at 3D local surface vibrations (with frequency fs) resulting in an excitation of Tollmien-Schlichting (TS) waves (having combination frequencies f+ = fs+fv and f- = fs - fv). The experiments were carried out in a low-turbulence level wind tunnel on a high-precision experimental model of long-laminar-run swept airfoil (sweep angle of 35°) at a freestream speed of about 10 m/s. Controlled localized 3D surface vibrations and 2D freestream vortices were generated by special disturbance sources. Quantitative characteristics of the studied receptivity mechanism (receptivity coefficients) were estimated.
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| 2. |
- 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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| 3. |
- Borodulin, V. I., et al.
(författare)
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Experimental and theoretical study of swept-wing boundary-layer instabilities. Three-dimensional Tollmien-Schlichting instability
- 2019
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Ingår i: Physics of fluids. - : AMER INST PHYSICS. - 1070-6631 .- 1089-7666. ; 31:11
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Tidskriftsartikel (refereegranskat)abstract
- Extensive combined experimental and theoretical investigations of the linear evolution of three-dimensional (3D) Tollmien-Schlichting (TS) instability modes of 3D boundary layers developing on a swept airfoil section have been carried out. The flow under consideration is the boundary layer over an airfoil at 350 sweep and an angle of attack of +1.5 degrees. At these conditions, TS instability is found to be the predominant one. Perturbations with different frequencies and spanwise wavenumbers are generated in a controlled way using a row of elastic membranes. All experimental results are deeply processed and compared with results of calculations based on theoretical approaches. Very good quantitative agreement of all measured and calculated stability characteristics of swept-wing boundary layers is achieved.
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| 4. |
- Borodulin, V. I., et al.
(författare)
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Experimental and theoretical study of swept-wing boundary-layer instabilities. Unsteady crossflow instability
- 2019
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Ingår i: Physics of fluids. - : AMER INST PHYSICS. - 1070-6631 .- 1089-7666. ; 31:6
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Tidskriftsartikel (refereegranskat)abstract
- Extensive combined experimental and theoretical investigations of the linear evolution of unsteady (in general) Cross-Flow (CF) and three-dimensional (3D) Tollmien-Schlichting (TS) instability modes of 3D boundary layers developing on a swept airfoil section have been carried out. CF-instability characteristics are investigated in detail at an angle of attack of -5 degrees when this kind of instability dominates in the laminar-turbulent transition process, while the 3D TS-instability characteristics are studied at an angle of attack of +1.5 degrees when this kind of instability is predominant in the transition process. All experimental results are deeply processed and compared with results of calculations based on several theoretical approaches. For the first time, very good quantitative agreement of all measured and calculated stability characteristics of swept-wing boundary layers is achieved both for unsteady CF- and 3D TS-instability modes for the case of a boundary layer developing on a real swept airfoil. The first part of the present study (this paper) is devoted to the description of the case of CF-dominated transition, while the TS-dominated case will be described in detail in a subsequent second part of this investigation.
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| 5. |
- 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
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Ingår i: AIP Conference Proceedings. - : American Institute of Physics Inc.. - 0094-243X. - 9780735417472
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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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| 6. |
- Armengaud, E., et al.
(författare)
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Model-based toolchain for the efficient development of safety-relevant automotive embedded systems
- 2011
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Ingår i: SAE technical paper series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Tidskriftsartikel (refereegranskat)abstract
- Advanced functionalities unthinkable a few decades ago are now being introduced into automotive vehicles through embedded systems for reasons like emission control, vehicle connectivity, safety and cooperative behaviors. As the development often involves stakeholders from different engineering disciplines and organizations, the complexity due to shared requirements, interdependencies of data, functions, and resources, as well as tight constraints in regards to timing, safety, and resource efficiency makes the system integration, quality control and assurance, reuse and change management increasingly more difficult. This calls for a more rigorous approach to the development of automotive embedded systems and components. This paper describes the CESAR reference technology platform (RTP) that supports the formalization of various engineering concerns in the development of safety-relevant embedded systems and thereby a model-based integration of various tools and methods to form seamless environments or toolchains for the development of such systems.
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| 7. |
- Tocci, F., et al.
(författare)
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The Effect of 2-D Surface Irregularities on Laminar-Turbulent Transition : A Comparison of Numerical Methodologies
- 2021
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Ingår i: Notes on Numerical Fluid Mechanics and Multidisciplinary Design. - Cham : Springer Nature. ; , s. 246-256
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Konferensbidrag (refereegranskat)abstract
- The applicability of Local Stability Theory (LST), Parabolized Stability Equations (PSE) and the Adaptive Harmonic Linearized Navier-Stokes (AHLNS) approach is investigated in the presence of 2-D surface irregularities through comparison with Direct Numerical Simulations (DNS). Remarkably good agreement between DNS and AHLNS is obtained for the amplification curves of Tollmien-Schlichting (TS) waves in all the cases studied. The LST and PSE results exhibit differences which are discussed in relation to the local distortion of the boundary layer induced by the irregularities.
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