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Alfredsson, P. HenrikORCID iD iconorcid.org/0000-0002-1146-3241
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Publications (10 of 194) Show all publications
Alfredsson, P. H., Kato, K. & Lingwood, R. (2024). Flows Over Rotating Disks and Cones. Annual Review of Fluid Mechanics, 56, 45-68
Open this publication in new window or tab >>Flows Over Rotating Disks and Cones
2024 (English)In: Annual Review of Fluid Mechanics, ISSN 0066-4189, E-ISSN 1545-4479, Vol. 56, p. 45-68Article, review/survey (Refereed) Published
Abstract [en]

Rotating-disk flows were first considered by von Karman in a seminal paper in 1921, where boundary layers in general were discussed and, in two of the nine sections, results for the laminar and turbulent boundary layers over a rotating disk were presented. It was not until in 1955 that flow visualization discovered the existence of stationary cross-flow vortices on the disk prior to the transition to turbulence. The rotating disk can be seen as a special case of rotating cones, and recent research has shown that broad cones behave similarly to disks, whereas sharp cones are susceptible to a different type of instability. Here, we provide a review of the major developments since von Karman's work from 100 years ago, regarding instability, transition, and turbulence in the boundary layers, and we include some analysis not previously published.

Place, publisher, year, edition, pages
Annual Reviews, 2024
Keywords
boundary layer stability, cross-flow vortices, absolute instability, roughness, transition, turbulence
National Category
Rheumatology and Autoimmunity
Identifiers
urn:nbn:se:kth:diva-343787 (URN)10.1146/annurev-fluid-121021-043651 (DOI)001153182300004 ()2-s2.0-85180410696 (Scopus ID)
Note

QC 20240222

Available from: 2024-02-22 Created: 2024-02-22 Last updated: 2024-03-05Bibliographically approved
Yimprasert, S., Kato, K., Alfredsson, P. H. & Matsubara, M. (2023). Effects of polymer addition on transition and length scales of flow structures in transitional channel flow. JOURNAL OF FLUID SCIENCE AND TECHNOLOGY, 18(1)
Open this publication in new window or tab >>Effects of polymer addition on transition and length scales of flow structures in transitional channel flow
2023 (English)In: JOURNAL OF FLUID SCIENCE AND TECHNOLOGY, ISSN 1880-5558, Vol. 18, no 1Article in journal (Refereed) Published
Abstract [en]

The effect of polymer addition on transition to turbulence in a two-dimensional water-flow channel was experimen-tally investigated by flow visualization using reflective flakes. The flow entering the channel test section maintains a high disturbance level by expanding laterally after reaching a high Reynolds number upstream the test section. In order to obtain the intermittency factor (turbulence fraction), the visualized images were classified into non-turbulent and turbulent regions, and the streamwise scale of the streaks appearing in the non-turbulent region was estimated from the autocorrelation coefficient computed by shifting the images in the streamwise direction. The visualization results show that similar to the pure water case, intermittent flow with a patch-like distribution of turbulent and non-turbulent areas clustered by streamwise streaks is observed. The Reynolds number at which the intermittency increases shifts toward higher Reynolds numbers with increasing polymer concentration, indicating a delay of transition. The streaks appearing in the non-turbulent region elongate with increasing polymer con-centration. At high concentrations, straight elongated streaks penetrate through the turbulent regions, suggesting that the polymer addition affects the stability of the streaks. These changes of the streak behavior indicate that the polymer affects not only the transition Reynolds number but also the flow structure during the transition process.

Place, publisher, year, edition, pages
Japan Society of Mechanical Engineers, 2023
Keywords
Flow visualization, Intermittency, Streamwise streak, Turbulent patch
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-328774 (URN)10.1299/jfst.2023jfst0021 (DOI)000984578000016 ()2-s2.0-85160346028 (Scopus ID)
Note

QC 20230613

Available from: 2023-06-13 Created: 2023-06-13 Last updated: 2023-06-13Bibliographically approved
Kato, K., Lingwood, R. J. & Alfredsson, P. H. (2023). Rotating disks and cones- a centennial of von Kármán’s 1921 paper. JOURNAL OF FLUID SCIENCE AND TECHNOLOGY, 18(1), JFST0003-JFST0003
Open this publication in new window or tab >>Rotating disks and cones- a centennial of von Kármán’s 1921 paper
2023 (English)In: JOURNAL OF FLUID SCIENCE AND TECHNOLOGY, ISSN 1880-5558, Vol. 18, no 1, p. JFST0003-JFST0003Article in journal (Refereed) Published
Abstract [en]

It is now more than 100 years since the work of von Karman (1921) on the boundary-layer flow over a rotating disk was published in the first volume of Zeitschrift fufr Angewandte Mathematik und Mechanik (ZAMM, Vol. 1(4), pp 233-252). Recently, there has been a large amount of work undertaken addressing the instability and transition of the boundary-layer flows over rotating disks and cones using theoretical, numerical and experimental techniques. Here we will discuss some different methods to analyze experimental data that can give insight into the instability and transition to turbulence of boundary-layer flows over rotating slender and broad cones (including the disk). At first, we discuss the pdf-method (probability density function) that allows a simple way to determine regions of instability growth, transition and fully developed turbulence. Secondly, we look at various ways to use spectral information to investigate the boundary layers giving a deeper understanding of the transition process. Finally, a method to determine the most probable flow structure leading up to fully developed turbulence is discussed. We envisage that some of these methods can be useful in analyzing instability and transition also in other flow cases.

Place, publisher, year, edition, pages
Japan Society of Mechanical Engineers, 2023
Keywords
Slender cones, Broad cones, Cross-flow instability, Centrifugal instability, Pdf-plot, Spectral plot, Flow-structure reconstruction
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-328430 (URN)10.1299/jfst.2023jfst0003 (DOI)000984578000020 ()2-s2.0-85160325500 (Scopus ID)
Note

QC 20230612

Available from: 2023-06-12 Created: 2023-06-12 Last updated: 2023-06-12Bibliographically approved
Kato, K., Segalini, A., Alfredsson, P. H. & Lingwood, R. (2022). Instabilities and Transition on a Rotating Cone-Old Problems and New Challenges. In: Sherwin, S Schmid, P Wu, X (Ed.), Laminar-Turbulent Transition: . Paper presented at 9th IUTAM Symposium on Laminar-Turbulent Transition, SEP 02-06, 2019, Imperial Coll London, London, ENGLAND (pp. 203-213). Springer Nature, 38
Open this publication in new window or tab >>Instabilities and Transition on a Rotating Cone-Old Problems and New Challenges
2022 (English)In: Laminar-Turbulent Transition / [ed] Sherwin, S Schmid, P Wu, X, Springer Nature , 2022, Vol. 38, p. 203-213Conference paper, Published paper (Refereed)
Abstract [en]

An experimental investigation of instabilities and transition in the boundary layer on a rotating broad (120 degrees apex angle) cone through hot-wire measurements combined with local linear stability analysis (LLSA) has been undertaken. The rotating-cone flow is susceptible to both cross-flow and centrifugal instabilities. For broad cones, the cross-flow instability dominates over the centrifugal instability, and vice versa for slender cones. Although stationary vortical disturbances from the cross-flow instability are dominant on the broad cone (in this case 24-26 vortices develop), we have identified an initially slowly growing nonstationary mode with a much smaller wavenumber, which close to transition increases its growth rate dramatically. We report on a detailed process to identify the wavenumber of the measured nonstationary disturbance, as well as quantitative comparisons between experimental results and LLSA.

Place, publisher, year, edition, pages
Springer Nature, 2022
Series
IUTAM Bookseries, ISSN 1875-3507
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-304788 (URN)10.1007/978-3-030-67902-6_17 (DOI)000709087600017 ()2-s2.0-85112659629 (Scopus ID)
Conference
9th IUTAM Symposium on Laminar-Turbulent Transition, SEP 02-06, 2019, Imperial Coll London, London, ENGLAND
Note

QC 20211123

Part of proceedings: ISBN 978-3-030-67902-6; 978-3-030-67901-9

Available from: 2021-11-23 Created: 2021-11-23 Last updated: 2024-03-18Bibliographically approved
Yimprasert, S., Kvick, M., Alfredsson, P. H. & Matsubara, M. (2021). Flow visualization and skin friction determination in transitional channel flow. Experiments in Fluids, 62(2), Article ID 31.
Open this publication in new window or tab >>Flow visualization and skin friction determination in transitional channel flow
2021 (English)In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 62, no 2, article id 31Article in journal (Refereed) Published
Abstract [en]

The present study experimentally determines the transitional Reynolds number range for plane channel flow and characterizes its transitional state. The pressure along the channel is measured to determine the skin friction coefficient as function of Reynolds number from the laminar state, through the transitional region into the fully turbulent state. The flow structure was studied through flow visualisation which shows that as the Reynolds number increases from the laminar state the transitional region starts showing randomly occurring turbulent spots. With increasing Reynolds number the spots shift into oblique patches and bands of small scale turbulence that form across the channel width, together with large-scale streaky structures found in areas between the turbulent regions. An image analysing technique was used to determine the intermittency factor, i.e. the turbulence fraction in the flow, as function of Reynolds number. It is found that the skin friction coefficient reaches its turbulent value before the flow is fully turbulent (the intermittency factor is still below one). This suggests that the observed streaky structures in non-turbulent regions contribute to the enhancement of the wall-normal transfer of momentum. Also above the Reynolds numbers where the turbulent skin friction coefficient has been established large-scale features consisting of irregular streaky structures are found. They have an oblique shape similar to the non-turbulent and turbulent patches in the transitional flow indicating that the transition process is not fully complete even above the Reynolds number where the skin friction reaches its turbulent level.

Place, publisher, year, edition, pages
SPRINGER, 2021
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-291919 (URN)10.1007/s00348-020-03102-6 (DOI)000616526800007 ()2-s2.0-85100298475 (Scopus ID)
Note

QC 20210323

Available from: 2021-03-23 Created: 2021-03-23 Last updated: 2022-06-25Bibliographically approved
Kato, K., Segalini, A., Alfredsson, P. H. & Lingwood, R. (2021). Instability and transition in the boundary layer driven by a rotating slender cone. Journal of Fluid Mechanics, 915, Article ID R4.
Open this publication in new window or tab >>Instability and transition in the boundary layer driven by a rotating slender cone
2021 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 915, article id R4Article in journal (Refereed) Published
Abstract [en]

Instability and transition in the boundary layer on a slender cone (600 apex angle) rotating in still fluid are investigated using hot-wire anemometry as well as through linear stability analysis. In contrast to broad cones (including the disk), where a cross-flow instability dominates the transition and different studies report similar transition Reynolds numbers, the reported transition Reynolds numbers on slender cones are scattered. The present experiments provide quantitative experimental datasets and the stability and transition are evaluated based on both the Reynolds number and a Girder number. The results consistently show that the instability development depends on the Gortler number rather than the Reynolds number and that transition starts at a well-defined Gortler number, whereas the transition Reynolds number depends on the rotational rate. The measured disturbance that first grows in the laminar region has a frequency approximately the same as or twice the rotational rate of the cone, which according to the stability analysis corresponds to the critical frequency of a slightly inclined vortex structure with respect to the cone axis or an axisymmetric vortex structure. These structures are similar to those observed in the flow visualisations of Kobayashi & Izumi (J. Fluid Mech., vol. 127, 1983, pp. 353-364) and considered as being due to a centrifugal instability.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS, 2021
Keywords
transition to turbulence
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-293382 (URN)10.1017/jfm.2021.216 (DOI)000635224600001 ()2-s2.0-85103581759 (Scopus ID)
Note

QC 20210427

Available from: 2021-04-27 Created: 2021-04-27 Last updated: 2022-10-24Bibliographically approved
Kato, K., Alfredsson, H. & Lingwood, R. (2021). Instability on Rotating Sharp Cones—Revisited. In: Progress in Turbulence IX: Proceedings of the iTi Conference in Turbulence 2021. Paper presented at 9th iTi Conference on Turbulence, iTi 2021, 25 February 2021 through 26 February 2021, Virtual, Online (pp. 259-265). Springer Nature, 267
Open this publication in new window or tab >>Instability on Rotating Sharp Cones—Revisited
2021 (English)In: Progress in Turbulence IX: Proceedings of the iTi Conference in Turbulence 2021, Springer Nature , 2021, Vol. 267, p. 259-265Conference paper, Published paper (Refereed)
Abstract [en]

We analyse the azimuthal velocity fluctuation in the boundary layer driven by a rotating slender cone with a half-cone apex angle of 30 ∘. The flow is dominated by a centrifugal instability, which develops into randomly occurring spiralling vortices travelling on the cone surface. Such non-stationary vortices are observed as an irregular wave packet-like fluctuation signal by a hot wire fixed in the lab frame of reference and the spectral map at different radial positions forms a smooth ridge, which is in contrast to the periodic time signal due to stationary crossflow vortices on broad cones, which gives rise to sharp spectral ridges. The present analysis decomposes the wave packet-like fluctuation using a short-time Fourier transform (STFT), revealing that the smooth spectral peak at a given radial position consists of waves with different frequencies. The most probable fundamental frequency follows the most unstable frequency according to linear stability theory. Also, we evaluate the amplitude of the harmonics of the most energetic mode around transition; quadratic nonlinear growth is observed until the amplitude of the fundamental mode saturates at transition. This behaviour is similar to that on broad cones although the primary instability and vortex structures are different.

Place, publisher, year, edition, pages
Springer Nature, 2021
Series
Springer Proceedings in Physics, ISSN 0930-8989 ; 267
Keywords
Boundary layers, Building wiring, Cones, Stability, Vortex flow, Azimuthal velocity, Centrifugal instability, Cone apex angles, Cone surfaces, Hot wires, Irregular waves, Nonstationary, Radial position, Stationary vortex, Velocity fluctuations, Wave packets
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-313232 (URN)10.1007/978-3-030-80716-0_35 (DOI)2-s2.0-85119000055 (Scopus ID)
Conference
9th iTi Conference on Turbulence, iTi 2021, 25 February 2021 through 26 February 2021, Virtual, Online
Note

QC 20220601

Part of proceedings: ISBN 978-303080715-3

Available from: 2022-06-01 Created: 2022-06-01 Last updated: 2022-06-25Bibliographically approved
Örlü, R., Tillmark, N. & Alfredsson, P. H. (2021). Measured critical size of roughness elements. Internal Publication
Open this publication in new window or tab >>Measured critical size of roughness elements
2021 (English)Report (Other academic)
Abstract [en]

This report describes wind-tunnel measurements within the RECEPT project to

determine transition behind a single roughness element placed near the leading

edge of a 35 degree swept airfoil at negative (-5 degrees) angle of attack with the

rotation axis parallel to the leading edge. A negative angle of attack decreases the

sensitivity to Tollmien-Schlichting wave-type instabilities and instead makes the

boundary layer flow mainly sensitive to cross-flow instability disturbances.

The airfoil was heated by blowing air through its hollow structure and transition

was detected through infrared (IR) temperature measurements of the airfoil

surface. The physical background behind the detection method is that if transition

occurs, the flow at the wall inside the turbulent wedge behind the roughness element

will have a larger friction than the laminar flow outside and hence a larger

heat transfer, making the wall temperature lower in this region. To confirm the

interpretation of the IR temperature images as well as provide measured boundary

layer parameters additional hot-wire measurements within the boundary layer

were performed at few of the parameters covered by the IR measurements. These

parameters are both related to the roughness elements themselves such as their

diameters and heights as well as free-stream velocities and turbulence levels of

the approaching flow.

Place, publisher, year, edition, pages
Internal Publication: , 2021. p. 71
Series
FP7–AAT-2010-RTD-1 265094 RECEPT
National Category
Engineering and Technology Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-291874 (URN)
Note

QC 20210710

Available from: 2021-03-22 Created: 2021-03-22 Last updated: 2022-06-25Bibliographically approved
Ito, T., Alfredsson, P. H., Segalini, A. & Matsubara, M. (2021). On Similarity of Turbulence Statistics of a Turbulent Planar Jet Taking the Static Pressure into Account. In: Progress in Turbulence IX: Proceedings of the iTi Conference in Turbulence 2021. Paper presented at 9th iTi Conference on Turbulence, iTi 2021, 25 February 2021 through 26 February 2021, Virtual, Online (pp. 43-49). Springer Science and Business Media Deutschland GmbH, 267
Open this publication in new window or tab >>On Similarity of Turbulence Statistics of a Turbulent Planar Jet Taking the Static Pressure into Account
2021 (English)In: Progress in Turbulence IX: Proceedings of the iTi Conference in Turbulence 2021, Springer Science and Business Media Deutschland GmbH , 2021, Vol. 267, p. 43-49Conference paper, Published paper (Refereed)
Abstract [en]

The pressure gradient in a jet is usually regarded as negligibly small when deriving the streamwise velocity profile from the momentum equations. In addition one assumes that the bulk streamwise momentum is conserved in the streamwise direction. On the other hand, it is known that the pressure distribution in the jet is well balanced with the square of the lateral velocity fluctuation, indicating that pressure is not negligible in the lateral momentum equation. The purpose of this study is to determine the importance of the pressure in the jet by evaluating balances in the streamwise and lateral momentum equations from experimental data measured by a static pressure tube and an X-probe. The turbulence fluctuations and the static pressure indicate similarities in their lateral distributions and are well balanced in the streamwise and lateral momentum equations. Although the contribution of the static pressure to the streamwise momentum is small, it is of the same order as that of the turbulent statistics in the lateral momentum equation.

Place, publisher, year, edition, pages
Springer Science and Business Media Deutschland GmbH, 2021
Series
Springer Proceedings in Physics, ISSN 0930-8989 ; 267
Keywords
Turbulence, Lateral momentum, Lateral velocities, Momentum equation, Planar jets, Static pressure, Streamwise directions, Streamwise velocity, Turbulence statistics, Velocity profiles, Well balanced, Momentum
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-313235 (URN)10.1007/978-3-030-80716-0_6 (DOI)2-s2.0-85118967363 (Scopus ID)
Conference
9th iTi Conference on Turbulence, iTi 2021, 25 February 2021 through 26 February 2021, Virtual, Online
Note

QC 20220602

Available from: 2022-06-02 Created: 2022-06-02 Last updated: 2022-06-25Bibliographically approved
Alfredsson, H., Segalini, A. & Örlü, R. (2021). The Diagnostic Plot—A Tutorial with a Ten Year Perspective. In: Progress in Turbulence IX: Proceedings of the iTi Conference in Turbulence 2021. Paper presented at 9th iTi Conference on Turbulence, iTi 2021, 25 February 2021 through 26 February 2021, Virtual, Online (pp. 125-135). Springer Nature, 267
Open this publication in new window or tab >>The Diagnostic Plot—A Tutorial with a Ten Year Perspective
2021 (English)In: Progress in Turbulence IX: Proceedings of the iTi Conference in Turbulence 2021, Springer Nature , 2021, Vol. 267, p. 125-135Conference paper, Published paper (Refereed)
Abstract [en]

The diagnostic plot was introduced in 2010 (Eur. J. Mech. B/Fluids 29: 403–406) but was used already in 2008 during a large measurement campaign as a litmus test to determine if tripped zero-pressure gradient turbulent boundary layers fulfilled basic criteria of being canonical. It used the rms-level of streamwise velocity (urms ) in the outer part of the boundary layer, a region where urms can give clear indications if insufficient or too tough tripping has been used. In standard plots one needs both the friction velocity and measurement of the full velocity and turbulence profiles. By instead plotting urms/ U∞ as a function of U/ U∞, it was found that this gives rise to a well-defined distribution that could be used as a canonical measure. It was later discovered that it is possible to extend the description to the near wall region. It has also been extended to boundary layers over rough surfaces and with pressure gradients, and some further uses. This paper aims to be both a review of the development of the method during the last 10+ years and a tutorial for those who want to employ it in their research and maybe also find new uses of the methodology.

Place, publisher, year, edition, pages
Springer Nature, 2021
Series
Springer Proceedings in Physics, ISSN 0930-8989 ; 267
Keywords
Atmospheric thermodynamics, Boundary layer flow, Pressure gradient, Turbulence, Turbulent flow
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-313231 (URN)10.1007/978-3-030-80716-0_17 (DOI)2-s2.0-85119016980 (Scopus ID)
Conference
9th iTi Conference on Turbulence, iTi 2021, 25 February 2021 through 26 February 2021, Virtual, Online
Note

QC 20220601

Part of proceedings: ISBN 978-303080715-3

Available from: 2022-06-01 Created: 2022-06-01 Last updated: 2022-06-25Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-1146-3241

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