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Fransson, Jens H. M.ORCID iD iconorcid.org/0000-0002-3251-8328
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Publications (10 of 132) Show all publications
Trip, R. & Fransson, J. H. M. (2017). Bluff body boundary-layer modification and its effect on the near-wake topology. Physics of fluids, 29(9), Article ID 095105.
Open this publication in new window or tab >>Bluff body boundary-layer modification and its effect on the near-wake topology
2017 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 29, no 9, article id 095105Article in journal (Refereed) Published
Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-216638 (URN)10.1063/1.5003383 (DOI)000412105100043 ()2-s2.0-85030183126 (Scopus ID)
Note

QC 20171101

Available from: 2017-11-01 Created: 2017-11-01 Last updated: 2017-11-01Bibliographically approved
Fransson, J. H. M. (2017). Free-stream turbulence and its influence on boundary-layer transition. In: 10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017: . Paper presented at 10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017, Swissotel ChicagoChicago, United States, 6 July 2017 through 9 July 2017. International Symposium on Turbulence and Shear Flow Phenomena, TSFP10, 2
Open this publication in new window or tab >>Free-stream turbulence and its influence on boundary-layer transition
2017 (English)In: 10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017, International Symposium on Turbulence and Shear Flow Phenomena, TSFP10 , 2017, Vol. 2Conference paper (Refereed)
Abstract [en]

Free-stream turbulence (FST) gives, undoubtedly, rise to the most complicated boundary-layer transition-toturbulence scenario. The reason for the complexity is that the boundary layer thickness grows with the downstream distance at the same time as the turbulence intensity (Tu) of the FST decays and the FST characteristic length scales grow. The FST is present everywhere in the free stream, but changes characteristics with the downstream distance. This implies that the actual forcing by the FST on the boundary layer changes gradually, which makes it an intricate receptivity problem. Today, we cannot honestly say that we are capable to accurately predict the transition location subject to FST in the simplest boundary layer flow, namely the one developing over a flat plat under zero-pressure gradient condition. Based on a set of original experimental data, consisting of 42 unique FST conditions, we here report on a semiempirical transition prediction model, which takes into account both the integral length scale and the turbulence velocity fluctuation at the leading edge. We show that the Tu, used in all existing models, is not the leading variable. Instead, our data show that the necessary ingredients in a successful transition prediction model includes, firstly, a FST Reynolds number (Refst) as leading variable, secondly, an FST parameter being the integral length scale Reynolds number (ReL) which further accounts for the effect of different length scales and, thirdly, a scale-matching model between the FST and the boundary layer. However, the importance of Tu can still be realized, since it constitutes the quotient of the two Reynolds numbers, namely Tu = Refst=ReL, even though Tu does not explicitly appear in the model.

Place, publisher, year, edition, pages
International Symposium on Turbulence and Shear Flow Phenomena, TSFP10, 2017
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-217847 (URN)2-s2.0-85033241121 (Scopus ID)
Conference
10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017, Swissotel ChicagoChicago, United States, 6 July 2017 through 9 July 2017
Note

QC 20171124

Available from: 2017-11-24 Created: 2017-11-24 Last updated: 2017-11-24Bibliographically approved
Camarri, S., Trip, R. & Fransson, J. H. M. (2017). Investigation of passive control of the wake past a thick plate by stability and sensitivity analysis of experimental data. Journal of Fluid Mechanics, 828, 753-778
Open this publication in new window or tab >>Investigation of passive control of the wake past a thick plate by stability and sensitivity analysis of experimental data
2017 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 828, p. 753-778Article in journal (Refereed) Published
Abstract [en]

In this paper we propose a strategy, entirely relying on available experimental data, to estimate the effect of a small control rod on the frequency of vortex shedding in the wake past a thick perforated plate. The considered values of the flow Reynolds number range between Re similar or equal to 6.6 x 10(3) and Re = 5.3 x 10(4). By means of particle image velocimetry, an experimental database consisting of instantaneous flow fields is collected for different values of suction through the body surface. The strategy proposed here is based on classical stability and sensitivity analysis applied to mean flow fields and on the formulation of an original ad hoc model for the mean flow. The mean flow model is obtained by calibrating the closure of the Reynolds averaged Navier-Stokes equations on the basis of the available experimental data through an optimisation algorithm. As a result, it is shown that the predicted control map agrees reasonably well with the equivalent one measured experimentally. Moreover, it is shown that even when turbulence effects are neglected, the stability analysis applied to the mean flow fields provides a reasonable estimation of the vortex shedding frequency, confirming what is known in the literature and extending it up to Re = 5.3 x 10(4). It is also shown that, when turbulence is taken into account in the stability analysis using the same closure that is calibrated for the corresponding mean flow model, the prediction of the vortex shedding frequency is systematically improved.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS, 2017
Keywords
instability, instability control, wakes
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-214866 (URN)10.1017/jfm.2017.531 (DOI)000410524800005 ()
Note

QC 20171024

Available from: 2017-10-24 Created: 2017-10-24 Last updated: 2017-10-24Bibliographically approved
Downs, R. S., Fallenius, B. E. G., Fransson, J. H. M. & Martensson, H. (2017). Miniature vortex generators for flow control in falkner-skan boundary layers. AIAA Journal, 55(2), 352-364
Open this publication in new window or tab >>Miniature vortex generators for flow control in falkner-skan boundary layers
2017 (English)In: AIAA Journal, ISSN 0001-1452, E-ISSN 1533-385X, Vol. 55, no 2, p. 352-364Article in journal (Refereed) Published
Abstract [en]

Vortex generators with heights comparable to displacement thickness are an effective means of producing persistent mean-flow streaks in laminar boundary layers. Inducing streaky base flows can suppress the growth of unsteady disturbances that would otherwise incite laminar-to-turbulent transition. Previous experimental and numerical works demonstrated the versatility of these miniature vortex generators in zero-pressure-gradient boundary layers. In this work, mean-flow disturbances developing from miniature vortex generators in adverse and favorable pressure-gradient boundary layers are measured systemically to assess the possibility of extending miniature vortex generator-based flow control to these scenarios. Boundary-layer streak amplitudes are measured across a range of Falkner-Skan m values, and an empirical scaling is found based on existing results. The effect of streaks on transition in an adverse pressure-gradient boundary layer is also tested, and moderate increases to laminar flow extents are observed.

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics Inc., 2017
Keywords
Boundary layer flow, Boundary layers, Flow control, Laminar flow, Pressure gradient, Turbulent flow, Vortex flow, Adverse pressure gradient, Boundary layer streaks, Displacement thickness, Favorable pressure gradients, Laminar to turbulent transitions, Streaky base flow, Unsteady disturbance, Zero-pressure-gradient boundary layers, Laminar boundary layer
National Category
Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-207422 (URN)10.2514/1.J055332 (DOI)000395555300002 ()2-s2.0-85012866259 (Scopus ID)
Note

QC 20170524

Available from: 2017-05-24 Created: 2017-05-24 Last updated: 2017-05-24Bibliographically approved
Sattarzadeh, S. S. & Fransson, J. H. M. (2017). Spanwise boundary layer modulations using finite discrete suction for transition delay. Experiments in Fluids, 58(3), Article ID 14.
Open this publication in new window or tab >>Spanwise boundary layer modulations using finite discrete suction for transition delay
2017 (English)In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 58, no 3, article id 14Article in journal (Refereed) Published
Abstract [en]

Discrete suction is deployed in a flat plate boundary layer to create spanwise mean velocity gradients (SVG) with the goal of delaying the onset of laminar-to-turbulent transition. It is shown that finite boundary layer suction through a set of holes in a spanwise oriented array in the flat plate is successful in setting up steady and robust streamwise streaks in the boundary layer. Today, the SVG method for transition control is known to attenuate the growth of Tollmien-Schlichting (TS) waves and delay the transition to turbulence. In this investigation, low-amplitude forced TS waves are attenuated with the implication of extending the laminar flow by at least 120% for a discrete suction of 0.8% of the free-stream velocity. The control technique is also tested successfully for natural transition, with a resulting transition delay of 30%.

Place, publisher, year, edition, pages
SPRINGER, 2017
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-205506 (URN)10.1007/s00348-017-2301-6 (DOI)000397980600003 ()2-s2.0-85012026192 (Scopus ID)
Note

QC 20170510

Available from: 2017-05-10 Created: 2017-05-10 Last updated: 2017-05-10Bibliographically approved
Trip, R. & Fransson, J. (2016). An experimental study on the relation between the wake inlet conditions and the near wake topology. In: Springer Proceedings in Physics: . Paper presented at 5th International Conference on Jets, Wakes and Separated Flows, ICJWSF2015, 15 June 2015 through 18 June 2015 (pp. 133-138). Springer Science+Business Media B.V.
Open this publication in new window or tab >>An experimental study on the relation between the wake inlet conditions and the near wake topology
2016 (English)In: Springer Proceedings in Physics, Springer Science+Business Media B.V., 2016, p. 133-138Conference paper, Published paper (Refereed)
Abstract [en]

A study on the relation between the wake inlet conditions and the wake characteristics of a bluff body by means of Particle Image Velocimetry is presented. The wake inlet condition, being a laminar boundary layer at the trailing edge of the body, are varied by means of wall-suction. Measurements are carried out at Reh = 6.7 × 103 based on the body thickness h. The induced radius of curvature of the streamlines is shown to be a promising parameter in explaining the increase in base drag and decrease in vortex shedding frequency associated with a thinner boundary layer.

Place, publisher, year, edition, pages
Springer Science+Business Media B.V., 2016
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-183541 (URN)10.1007/978-3-319-30602-5_17 (DOI)000387431400017 ()2-s2.0-84979031674 (Scopus ID)9783319306001 (ISBN)
Conference
5th International Conference on Jets, Wakes and Separated Flows, ICJWSF2015, 15 June 2015 through 18 June 2015
Note

QC 20160316

Available from: 2016-03-16 Created: 2016-03-16 Last updated: 2017-02-23Bibliographically approved
Downs, R. S. ,., Fallenius, B. E. G., Fransson, J. H. M. & Mårtensson, H. (2016). Evaluation of miniature vortex generators for flow control in Falkner-Skan boundary layers. In: 54th AIAA Aerospace Sciences Meeting: . Paper presented at 54th AIAA Aerospace Sciences Meeting, 2016, 4 January 2016 through 8 January 2016. American Institute of Aeronautics and Astronautics
Open this publication in new window or tab >>Evaluation of miniature vortex generators for flow control in Falkner-Skan boundary layers
2016 (English)In: 54th AIAA Aerospace Sciences Meeting, American Institute of Aeronautics and Astronautics, 2016Conference paper, Published paper (Refereed)
Abstract [en]

Vortex generators with heights comparable to displacement thickness are an effective means of producing persistent mean-flow streaks in laminar boundary layers. Inducing streaky base flows can suppress growth of unsteady disturbances which would otherwise incite laminar-to-turbulent transition. Previous experimental and numerical works have demonstrated the versatility of these miniature vortex generators (MVGs) in zero pressure gradient boundary layers. In this work, mean-flow disturbances developing from MVGs in adverse and favorable pressure gradient boundary layers are measured systemically to assess the possibility of extending MVG-based flow control to these scenarios. Boundary-layer streak amplitudes are measured across a range of Falkner-Skan m values and an empirical scaling is found in congruence with existing results. The effect of streaks on transition in an adverse pressure gradient boundary layer is also tested and moderate increases to laminar flow extents are observed.

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics, 2016
Keywords
Aerospace engineering, Aviation, Boundary layer flow, Boundary layers, Flow control, Laminar flow, Pressure gradient, Turbulent flow, Vortex flow, Adverse pressure gradient, Boundary layer streaks, Displacement thickness, Empirical scaling, Favorable pressure gradients, Laminar to turbulent transitions, Unsteady disturbance, Zero-pressure-gradient boundary layers, Laminar boundary layer
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-201981 (URN)2-s2.0-85007439486 (Scopus ID)9781624103933 (ISBN)
Conference
54th AIAA Aerospace Sciences Meeting, 2016, 4 January 2016 through 8 January 2016
Note

Funding text: This work is part of the MOTSTRÖM project and is funded by VINNOVA through Nationella ygtekniska forskningsprogrammet (NFFP).

QC 20170303

Available from: 2017-03-03 Created: 2017-03-03 Last updated: 2017-03-03Bibliographically approved
Sattarzadeh, S. S. & Fransson, J. H. M. (2016). Mastering nonlinear flow dynamics for laminar flow control. Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 94(2), Article ID 021103.
Open this publication in new window or tab >>Mastering nonlinear flow dynamics for laminar flow control
2016 (English)In: Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, ISSN 2470-0045, Vol. 94, no 2, article id 021103Article in journal (Refereed) Published
Abstract [en]

A laminar flow control technique based on spanwise mean velocity gradients (SVGs) has recently proven successful in delaying transition in boundary layers. Here we take advantage of a well-known nonlinear effect, namely, the interaction of two oblique waves at high amplitude, to produce spanwise mean velocity variations. Against common belief we are able to fully master the first stage of this nonlinear interaction to generate steady and stable streamwise streaks, which in turn trigger the SVG method. Our experimental results show that the region of laminar flow can be extended by up to 230%.

Place, publisher, year, edition, pages
American Physical Society, 2016
Keywords
Boundary-Layer-Transition, Waves, Stabilization, Stability, Streaks
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-192392 (URN)10.1103/PhysRevE.94.021103 (DOI)000381607300001 ()2-s2.0-84983544085 (Scopus ID)
Funder
EU, European Research Council, ERC-StG-2010-258339
Note

QC 20160912

Available from: 2016-09-12 Created: 2016-09-12 Last updated: 2016-12-02Bibliographically approved
Siconolfi, L., Camarri, S. & Fransson, J. H. M. (2015). Boundary layer stabilization using free-stream vortice. Journal of Fluid Mechanics, 764, R2
Open this publication in new window or tab >>Boundary layer stabilization using free-stream vortice
2015 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 764, p. R2-Article in journal (Refereed) Published
Abstract [en]

In this numerical investigation we explore the possibility of applying free-stream vortices as a passive flow control method for delaying the transition to turbulence. The work is motivated by previous experimental studies demonstrating that stable streamwise boundary layer (BL) streaks can attenuate both two-and three-dimensional disturbances inside the BL, leading to transition delay, with the implication of reducing skin-friction drag. To date, successful control has been obtained using physical BL modulators mounted on the surface in order to generate stable streaks. However, surface mounted BL modulators are doomed to failure when the BL is subject to free-stream turbulence (FST), since a destructive interaction between the two is inevitable. In order to tackle free-stream disturbances, such as FST, a smooth surface is desired, which has motivated us to seek new methods to induce streamwise streaks inside the BL. A first step, in a systematic order, is taken in the present paper to prove the control idea of generating free-stream vortices for the attenuation of ordinary Tollmien-Schlichting waves inside the BL. In this proof-of-concept study we show that, by applying a spanwise array of counter-rotating free-stream vortices, inducing streamwise BL streaks further downstream, it is possible to alter the BL stability characteristics to such a degree that transition delay may be accomplished. For the demonstration we use direct numerical simulations along with stability analysis.

Keywords
boundary layer control, drag reduction, transition to turbulence
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-160373 (URN)10.1017/jfm.2014.731 (DOI)000348128700002 ()2-s2.0-84927138962 (Scopus ID)
Funder
EU, European Research Council
Note

QC 20150227

Available from: 2015-02-27 Created: 2015-02-19 Last updated: 2017-12-04Bibliographically approved
Sattarzadeh, S. S. & Fransson, J. H. M. (2015). On the scaling of streamwise streaks and their efficiency to attenuate Tollmien-Schlichting waves. Experiments in Fluids, 56(3), Article ID 58.
Open this publication in new window or tab >>On the scaling of streamwise streaks and their efficiency to attenuate Tollmien-Schlichting waves
2015 (English)In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 56, no 3, article id 58Article in journal (Refereed) Published
Abstract [en]

Streaky boundary layers generated by an array of miniature vortex generators (MVGs) mounted on a flat plate have recently shown to have a stabilizing effect on both two-and three-dimensional disturbances. An experimental study on the effect of the geometrical parameters of MVGs on the generated streamwise streaks in the flat plate boundary layer is carried out, and the corresponding stabilizing effect on Tollmien-Schlichting (TS) wave disturbances is quantified. The new experimental configurations have led to an improved empirical scaling law, which includes additional geometrical parameters of the MVGs compared to the previously reported relation. It is found that the MVG configuration can be optimized with respect to the attenuation of disturbances. In addition, the streamwise location of branch I of the neutral stability curve, with regard to the location of the MVG array, is found to be correlated with the initial receptivity of TS waves on the MVG array and the attenuation of the TS wave amplitude in the unstable region.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-139048 (URN)10.1007/s00348-015-1930-x (DOI)000350688000011 ()2-s2.0-84928666620 (Scopus ID)
Funder
EU, European Research Council
Note

QC 20150423. Updated from manuscript to article in journal.

Available from: 2013-12-30 Created: 2013-12-30 Last updated: 2017-12-06Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-3251-8328

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