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BETA
Fransson, Jens H. M.ORCID iD iconorcid.org/0000-0002-3251-8328
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Publications (10 of 133) Show all publications
Fransson, J. H. M., Mamidala, S. B., Fallenius, B. E. G., Mårtensson, H. & Wallin, F. (2018). An experimental setup for idealised studies on transition to turbulence on a generic compressor outlet guide vane. In: Proceedings of the ASME Turbo Expo: . Paper presented at Volume 2A-2018, 2018ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, GT 2018, Oslo, Norway, 11 June 2018 through 15 June 2018;. ASME Press, Volume 2A-2018, 2018
Open this publication in new window or tab >>An experimental setup for idealised studies on transition to turbulence on a generic compressor outlet guide vane
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2018 (English)In: Proceedings of the ASME Turbo Expo, ASME Press, 2018, Vol. Volume 2A-2018, 2018Conference paper, Published paper (Refereed)
Abstract [en]

The understanding of flow phenomena in turbomachinery has come far with respect to three-dimensional flow patterns and pressure distributions. Much is due to improved measurements and a continuously evolving fidelity in computational fluid dynamics (CFD). Turbulence and transition in boundary layers are two classical areas where improvements in modeling are desired and where experimental validation is required. Apart from this, fundamental improvements in efficiency can be obtained by developing experimental resources where technologies affecting transition can be studied. The reduction in friction drag can be considerable if the transition to turbulence can be delayed. An experimental setup in an idealized configuration has been designed and built with the objective to study transition on a very large-scale guide vane profile at low speed. The purpose of the rig is to enable high quality fundamental studies of technologies to delay transition, but also to see how effects of manufacturing or other constraints may affect the boundary layer. In the present paper we report the first validation of the experimental setup, by comparing the first test results to CFD calculations performed during the rig design, i.e. no post-calculations with experimental data as input to the simulations have been done yet. The pressure distribution is in line with the design intent, which is a good indicator that the tunnel design is suitable for the intended purpose. At last we report some velocity measurements performed in the wake and we calculate the total drag based on the wake velocity deficit for various Reynolds numbers and with and without turbulence tripping tape. We illustrate that a two dimensional tripping around 7% of the chord from the leading edge can increase the total drag by 50% with respect to the reference case without tripping tape

Place, publisher, year, edition, pages
ASME Press, 2018
Series
Proceedings of the ASME Turbo Expo
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-238428 (URN)10.1115/GT201876507 (DOI)2-s2.0-85054023604 (Scopus ID)9780791850992 (ISBN)
Conference
Volume 2A-2018, 2018ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, GT 2018, Oslo, Norway, 11 June 2018 through 15 June 2018;
Note

QC 20181105

Available from: 2018-11-05 Created: 2018-11-05 Last updated: 2018-11-05Bibliographically approved
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 ()2-s2.0-85049774326 (Scopus ID)
Note

QC 20171024

Available from: 2017-10-24 Created: 2017-10-24 Last updated: 2018-10-16Bibliographically 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
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ORCID iD: ORCID iD iconorcid.org/0000-0002-3251-8328

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