| 1. |
- Bailey, S. C. C., et al.
(författare)
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Obtaining accurate mean velocity measurements in high Reynolds number turbulent boundary layers using Pitot tubes
- 2013
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Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 715, s. 642-670
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Tidskriftsartikel (refereegranskat)abstract
- This article reports on one component of a larger study on measurement of the zero-pressure-gradient turbulent flat plate boundary layer, in which a detailed investigation was conducted of the suite of corrections required for mean velocity measurements performed using Pitot tubes. In particular, the corrections for velocity shear across the tube and for blockage effects which occur when the tube is in close proximity to the wall were investigated using measurements from Pitot tubes of five different diameters, in two different facilities, and at five different Reynolds numbers ranging from Reθ = 11 100 to 67 000. Only small differences were found amongst commonly used corrections for velocity shear, but improvements were found for existing near-wall proximity corrections. Corrections for the nonlinear averaging of the velocity fluctuations were also investigated, and the results compared to hot-wire data taken as part of the same measurement campaign. The streamwise turbulence-intensity correction was found to be of comparable magnitude to that of the shear correction, and found to bring the hot-wire and Pitot results into closer agreement when applied to the data, along with the other corrections discussed and refined here.
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| 2. |
- Borodulin, V. I., et al.
(författare)
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Characteristics of 3D instability of a 35-degree swept wing to CF and TS modes. Experiment and theory
- 2016
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Ingår i: AIP Conference Proceedings. - : American Institute of Physics (AIP). - 0094-243X. - 9780735414280
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Konferensbidrag (refereegranskat)abstract
- An extensive experimental investigation of linear evolution of Cross-Flow (CF) and Tollmien-Schlichting (TS) modes of 3D boundary layer oscillations on a swept wing has been carried out. TS-instability characteristics have been studied experimentally for the first time. The characteristics of development of the two kinds of instability modes are compared with calculations and display a very good agreement. The whole dataset may be used for promotion of theoretical methods of investigation of laminar-turbulent transition in swept wing boundary layers.
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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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
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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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| 7. |
- 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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| 8. |
- Bourgoin, M., et al.
(författare)
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Investigation of the small-scale statistics of turbulence in the Modane S1MA wind tunnel
- 2018
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Ingår i: CEAS Aeronautical Journal. - : Springer. - 1869-5582 .- 1869-5590. ; 9:2, s. 269-281
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Tidskriftsartikel (refereegranskat)abstract
- This article describes the planning, set-up, turbulence characterization and analysis of measurements of a passive grid turbulence experiment that was carried out in the S1MA wind-tunnel from ONERA in Modane, in the context of the ESWIRP European project. This experiment aims at a detailed investigation of the statistical properties of turbulent flows at large Reynolds numbers. The primary goal is to take advantage of the unequaled large-scale dimensions of the ONERA S1MA wind-tunnel facility, to make available to the broad turbulence community high-quality experimental turbulence data with unprecendented resolution (both spatial and temporal) and accuracy (in terms of statistical convergence). With this goal, we designed the largest grid-generated turbulence experiment planned and performed to date. Grid turbulence is a canonical flow known to produce almost perfectly homogeneous and isotropic turbulence (HIT) which remains a unique framework to investigate fundamental physics of turbulent flows. Here, we present a brief description of the measurements, in particular those based on hot-wire diagnosis. By comparing results from classical hot-wires and from a nano-fabricated wire (developed at Princeton University), we show that our goal of resolving down to the smallest dissipative scales of the flow has been achieved. We also present the full characterization of the turbulence here, in terms of turbulent energy dissipation rate, injection and dissipation scales (both spatial and temporal) and Reynolds number.
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| 9. |
- Chan, C. , I, et al.
(författare)
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Large-scale and small-scale contribution to the skin friction reduction in a modified turbulent boundary layer by a large-eddy break-up device
- 2022
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Ingår i: Physical Review Fluids. - : American Physical Society (APS). - 2469-990X. ; 7:3
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Tidskriftsartikel (refereegranskat)abstract
- The role of streamwise length scales (lambda x) in turbulent skin friction generation is investigated using a direct numerical simulation data set of an incompressible zero pressure gradient turbulent boundary layer and the spectral analysis based on the FukagataL73 (2002)]. The total skin friction generation associated with motions scaled with local boundary layer thickness delta of lambda x 3 delta and lambda x 3 delta) contribute to a significant portion of turbulent skin friction. However, it is found that the large-scale ejection and sweep events with streamwise length scales at lambda x 3 delta are equally important. The turbulent skin friction reduction associated with the modification of largeand small-scale quadrant events is studied, using well-resolved simulation data sets of a large-eddy break-up (LEBU) device in a turbulent boundary layer. The results reveal that LEBUs modify both the large- and small-scale ejection and sweep events, yielding a substantial turbulent skin friction reduction.
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| 10. |
- Chan, I. C., et al.
(författare)
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The skin-friction coefficient of a turbulent boundary layer modified by a large-eddy break-up device
- 2021
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Ingår i: Physics of fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 33:3
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Tidskriftsartikel (refereegranskat)abstract
- A computational study based on well-resolved large-eddy simulations is performed to study the skin friction modification by a large-eddy breakup device (LEBU) in a zero-pressure-gradient turbulent boundary layer. The LEBU was modeled using an immersed boundary method. It is observed that the presence of the device leads to the generation of wake vortices, which propagate downstream from the LEBU and toward the wall. A skin friction decomposition procedure is utilized to study different physical mechanisms of the observed skin friction reduction. From the skin friction decomposition, it is found that the skin friction reduction can be characterized by three universal regions of different changes for the skin friction contributions. The first region is predominantly associated with the formation of the wake vortices and the reduction of Reynolds shear stress. In the second region, the mean streamwise velocity fields show that a region of velocity deficit formed downstream of the LEBU propagates toward the wall and leads to turbulence reduction due to wake wall interactions, which also induces a local maximum skin friction reduction. In the third region, the dissipation of wake vortices leads to the regeneration of Reynolds shear stress. A quadrant analysis of the Reynolds shear stress contribution reveals that the LEBU increases the Q2 and Q4 contributions and attenuates the Q1 and Q3 contributions in the first region, followed by an onset of Reynolds shear stress further downstream.
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