| 1. |
- Alfredsson, P. Henrik, et al.
(författare)
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Flows Over Rotating Disks and Cones
- 2024
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Ingår i: Annual Review of Fluid Mechanics. - : Annual Reviews. - 0066-4189 .- 1545-4479. ; 56, s. 45-68
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Forskningsöversikt (refereegranskat)abstract
- 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.
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| 2. |
- Kato, Kentaro, et al.
(författare)
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Boundary-layer transition over a rotating broad cone
- 2019
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Ingår i: Physical Review Fluids. - : American Physical Society. - 2469-990X. ; 4:7
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Tidskriftsartikel (refereegranskat)abstract
- The route to turbulence in the boundary layer on a rotating broad cone is investigated using hot-wire anemometry measuring the azimuthal velocity. The stationary fundamental mode is triggered by 24 deterministic small roughness elements distributed evenly at a specific distance from the cone apex. The stationary vortices, having a wave number of 24, correspond to the fundamental mode and these are initially the dominant disturbance-energy carrying structures. This mode is found to saturate and is followed by rapid growth of the nonstationary primary mode as well as the stationary and nonstationary first harmonics, leading to transition to turbulence. The amplitudes of these are plotted in a way to highlight the continued growth after saturation of the fundamental stationary mode.
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| 3. |
- Kato, Kentaro, et al.
(författare)
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Instabilities and Transition on a Rotating Cone-Old Problems and New Challenges
- 2022
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Ingår i: Laminar-Turbulent Transition. - Cham : Springer Nature. ; , s. 203-213
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 4. |
- Kato, Kentaro, Dr, 1987-, et al.
(författare)
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Instability and transition in the boundary layer driven by a rotating slender cone
- 2021
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Ingår i: Journal of Fluid Mechanics. - : CAMBRIDGE UNIV PRESS. - 0022-1120 .- 1469-7645. ; 915
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Kato, Kentaro, Dr, 1987-, et al.
(författare)
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Instability on Rotating Sharp Cones—Revisited
- 2021
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Ingår i: Progress in Turbulence IX. - Cham : Springer Nature. ; , s. 259-265
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 6. |
- Kato, Kentaro, et al.
(författare)
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Investigation of the structures in the unstable rotating-cone boundary layer
- 2019
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Ingår i: Physical Review Fluids. - : AMER PHYSICAL SOC. - 2469-990X. ; 4:5
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Tidskriftsartikel (refereegranskat)abstract
- This work reports on the unstable region and the transition process of the boundary-layer flow induced by a rotating cone with a half apex angle of 60 degrees using the probability density function (PDF) contour map of the azimuthal velocity fluctuation, which was first used by Imayama et al. [Phys. Fluids 24, 031701 (2012)] for the similar boundary-layer flow induced by a rotating disk. The PDF shows that the transition behavior of the rotating-cone flow is similar to that on the rotating disk. The effects of roughness elements on the cone surface have been examined. For the cone with roughnesses, we reconstructed the most probable vortex structure within the boundary layer from the hot-wire anemometry time signals. The results show that the PDF clearly describes the overturning process of the high-momentum upwelling of the spiral vortices, which due to vortex meandering cannot be detected in the phase-averaged velocity field reconstructed from the point measurements. At a late stage of the overturning process, our hot-wire measurements captured high-frequency oscillations, which may be related to secondary instability.
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| 7. |
- Kato, Kentaro, et al.
(författare)
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Rotating disks and cones- a centennial of von Kármán’s 1921 paper
- 2023
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Ingår i: JOURNAL OF FLUID SCIENCE AND TECHNOLOGY. - : Japan Society of Mechanical Engineers. - 1880-5558. ; 18:1, s. JFST0003-JFST0003
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Kato, Shuri, et al.
(författare)
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Clone identification in Japanese flowering cherry (Prunus subgenus Cerasus) cultivars using nuclear SSR markers
- 2012
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Ingår i: Breeding Science. - : Japanese Society of Breeding. - 1344-7610 .- 1347-3735. ; 62:3, s. 248-255
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Tidskriftsartikel (refereegranskat)abstract
- Numerous cultivars of Japanese flowering cherry (Prunus subgenus Cerasus) are recognized, but in many cases they are difficult to distinguish morphologically. Therefore, we evaluated the clonal status of 215 designated cultivars using 17 SSR markers. More than half the cultivars were morphologically distinct and had unique genotypes. However, 22 cultivars were found to consist of multiple clones, which probably originate from the chance seedlings, suggesting that their unique characteristics have not been maintained through propagation by grafting alone. We also identified 23 groups consisting of two or more cultivars with identical genotypes. Most members of these groups were putatively synonymously related and morphologically identical. However, some of them were probably derived from bud sport mutants and had distinct morphologies. SSR marker analysis provided useful insights into the clonal status of the examined Japanese flowering cherry cultivars and proved to be a useful tool for cultivar characterization.
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| 9. |
- Kato, Shuri, et al.
(författare)
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Origins of Japanese flowering cherry (Prunus subgenus Cerasus) cultivars revealed using nuclear SSR markers
- 2014
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Ingår i: Tree Genetics & Genomes. - : Springer Science and Business Media LLC. - 1614-2942 .- 1614-2950. ; 10:3, s. 477-487
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Tidskriftsartikel (refereegranskat)abstract
- Japanese flowering cherry (Prunus subgenus Cerasus) cultivars, which are characterized by beautiful flowers, have been developed through hybridization among wild Prunus taxa. The long history of cultivation has caused significant confusion over the origins of these cultivars. We conducted molecular analysis using nuclear simple sequence repeat (SSR) polymorphisms to trace cultivar origins. Bayesian clustering based on the STRUCTURE analysis using SSR genotypes revealed that many cultivars originated from hybridization between two or more wild species. This suggests that morphological variations among flowering cherry cultivars probably arose through a complex sequence of hybridizations. Our findings generally supported estimates of the origins of cultivars based on morphological study, although there were some exceptions.
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| 10. |
- Okita, Yukari, et al.
(författare)
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The transcription factor MAFK induces EMT and malignant progression of triple-negative breast cancer cells through its target GPNMB
- 2017
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Ingår i: Science Signaling. - : AMER ASSOC ADVANCEMENT SCIENCE. - 1945-0877 .- 1937-9145. ; 10:474
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Tidskriftsartikel (refereegranskat)abstract
- Triple-negative breast cancer (TNBC) is particularly aggressive and difficult to treat. For example, the transforming growth factor-beta (TGF-beta) pathway is implicated in TNBC progression and metastasis, but its opposing role in tumor suppression in healthy tissues and early-stage lesions makes it a challenging target. Therefore, additional molecular characterization of TNBC may lead to improved patient prognosis by informing the development and optimum use of targeted therapies. We found that musculoaponeurotic fibrosarcoma (MAF) oncogene family protein K (MAFK), a member of the small MAF family of transcription factors that are induced by the TGF-beta pathway, was abundant in human TNBC and aggressive mouse mammary tumor cell lines. MAFK promoted tumorigenic growth and metastasis by 4T1 cells when implanted subcutaneously in mice. Overexpression of MAFK in mouse breast epithelial NMuMG cells induced epithelial-mesenchymal transition (EMT) phenotypes and promoted tumor formation and invasion in mice. MAFK induced the expression of the gene encoding the transmembrane glycoprotein nmb(GPNMB). Similar to MAFK, GPNMB overexpression in NMuMG cells induced EMT, tumor formation, and invasion, in mice, whereas knockdown of MAFK in tumor cells before implantation suppressed tumor growth and progression. MAFK and GPNMB expression correlated with poor prognosis in TNBC patients. These findings suggest that MAFK and its target gene GPNMB play important roles in the malignant progression of TNBC cells, offering potentially new therapeutic targets for TNBC patients.
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