--- _id: '291' abstract: - lang: eng text: Over the past decade, the edge of chaos has proven to be a fruitful starting point for investigations of shear flows when the laminar base flow is linearly stable. Numerous computational studies of shear flows demonstrated the existence of states that separate laminar and turbulent regions of the state space. In addition, some studies determined invariant solutions that reside on this edge. In this paper, we study the unstable manifold of one such solution with the aid of continuous symmetry reduction, which we formulate here for the simultaneous quotiening of axial and azimuthal symmetries. Upon our investigation of the unstable manifold, we discover a previously unknown traveling-wave solution on the laminar-turbulent boundary with a relatively complex structure. By means of low-dimensional projections, we visualize different dynamical paths that connect these solutions to the turbulence. Our numerical experiments demonstrate that the laminar-turbulent boundary exhibits qualitatively different regions whose properties are influenced by the nearby invariant solutions. article_number: '054401' article_processing_charge: No author: - first_name: Nazmi B full_name: Budanur, Nazmi B id: 3EA1010E-F248-11E8-B48F-1D18A9856A87 last_name: Budanur orcid: 0000-0003-0423-5010 - first_name: Björn full_name: Hof, Björn id: 3A374330-F248-11E8-B48F-1D18A9856A87 last_name: Hof orcid: 0000-0003-2057-2754 citation: ama: Budanur NB, Hof B. Complexity of the laminar-turbulent boundary in pipe flow. Physical Review Fluids. 2018;3(5). doi:10.1103/PhysRevFluids.3.054401 apa: Budanur, N. B., & Hof, B. (2018). Complexity of the laminar-turbulent boundary in pipe flow. Physical Review Fluids. American Physical Society. https://doi.org/10.1103/PhysRevFluids.3.054401 chicago: Budanur, Nazmi B, and Björn Hof. “Complexity of the Laminar-Turbulent Boundary in Pipe Flow.” Physical Review Fluids. American Physical Society, 2018. https://doi.org/10.1103/PhysRevFluids.3.054401. ieee: N. B. Budanur and B. Hof, “Complexity of the laminar-turbulent boundary in pipe flow,” Physical Review Fluids, vol. 3, no. 5. American Physical Society, 2018. ista: Budanur NB, Hof B. 2018. Complexity of the laminar-turbulent boundary in pipe flow. Physical Review Fluids. 3(5), 054401. mla: Budanur, Nazmi B., and Björn Hof. “Complexity of the Laminar-Turbulent Boundary in Pipe Flow.” Physical Review Fluids, vol. 3, no. 5, 054401, American Physical Society, 2018, doi:10.1103/PhysRevFluids.3.054401. short: N.B. Budanur, B. Hof, Physical Review Fluids 3 (2018). date_created: 2018-12-11T11:45:39Z date_published: 2018-05-30T00:00:00Z date_updated: 2023-09-11T12:45:44Z day: '30' department: - _id: BjHo doi: 10.1103/PhysRevFluids.3.054401 external_id: arxiv: - '1802.01918' isi: - '000433426200001' intvolume: ' 3' isi: 1 issue: '5' language: - iso: eng main_file_link: - open_access: '1' url: https://arxiv.org/abs/1802.01918 month: '05' oa: 1 oa_version: Preprint publication: Physical Review Fluids publication_status: published publisher: American Physical Society publist_id: '7590' quality_controlled: '1' scopus_import: '1' status: public title: Complexity of the laminar-turbulent boundary in pipe flow type: journal_article user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1 volume: 3 year: '2018' ... --- _id: '17' abstract: - lang: eng text: Creeping flow of polymeric fluid without inertia exhibits elastic instabilities and elastic turbulence accompanied by drag enhancement due to elastic stress produced by flow-stretched polymers. However, in inertia-dominated flow at high Re and low fluid elasticity El, a reduction in turbulent frictional drag is caused by an intricate competition between inertial and elastic stresses. Here we explore the effect of inertia on the stability of viscoelastic flow in a broad range of control parameters El and (Re,Wi). We present the stability diagram of observed flow regimes in Wi-Re coordinates and find that the instabilities' onsets show an unexpectedly nonmonotonic dependence on El. Further, three distinct regions in the diagram are identified based on El. Strikingly, for high-elasticity fluids we discover a complete relaminarization of flow at Reynolds number in the range of 1 to 10, different from a well-known turbulent drag reduction. These counterintuitive effects may be explained by a finite polymer extensibility and a suppression of vorticity at high Wi. Our results call for further theoretical and numerical development to uncover the role of inertial effect on elastic turbulence in a viscoelastic flow. article_number: '103302 ' article_processing_charge: No author: - first_name: Atul full_name: Varshney, Atul id: 2A2006B2-F248-11E8-B48F-1D18A9856A87 last_name: Varshney orcid: 0000-0002-3072-5999 - first_name: Victor full_name: Steinberg, Victor last_name: Steinberg citation: ama: Varshney A, Steinberg V. Drag enhancement and drag reduction in viscoelastic flow. Physical Review Fluids. 2018;3(10). doi:10.1103/PhysRevFluids.3.103302 apa: Varshney, A., & Steinberg, V. (2018). Drag enhancement and drag reduction in viscoelastic flow. Physical Review Fluids. American Physical Society. https://doi.org/10.1103/PhysRevFluids.3.103302 chicago: Varshney, Atul, and Victor Steinberg. “Drag Enhancement and Drag Reduction in Viscoelastic Flow.” Physical Review Fluids. American Physical Society, 2018. https://doi.org/10.1103/PhysRevFluids.3.103302. ieee: A. Varshney and V. Steinberg, “Drag enhancement and drag reduction in viscoelastic flow,” Physical Review Fluids, vol. 3, no. 10. American Physical Society, 2018. ista: Varshney A, Steinberg V. 2018. Drag enhancement and drag reduction in viscoelastic flow. Physical Review Fluids. 3(10), 103302. mla: Varshney, Atul, and Victor Steinberg. “Drag Enhancement and Drag Reduction in Viscoelastic Flow.” Physical Review Fluids, vol. 3, no. 10, 103302, American Physical Society, 2018, doi:10.1103/PhysRevFluids.3.103302. short: A. Varshney, V. Steinberg, Physical Review Fluids 3 (2018). date_created: 2018-12-11T11:44:11Z date_published: 2018-10-15T00:00:00Z date_updated: 2023-09-11T12:59:28Z day: '15' ddc: - '532' department: - _id: BjHo doi: 10.1103/PhysRevFluids.3.103302 ec_funded: 1 external_id: isi: - '000447311500001' file: - access_level: open_access checksum: e1445be33e8165114e96246275600750 content_type: application/pdf creator: system date_created: 2018-12-12T10:10:14Z date_updated: 2020-07-14T12:45:12Z file_id: '4800' file_name: IST-2018-1061-v1+1_PhysRevFluids.3.103302.pdf file_size: 1409040 relation: main_file file_date_updated: 2020-07-14T12:45:12Z has_accepted_license: '1' intvolume: ' 3' isi: 1 issue: '10' language: - iso: eng month: '10' oa: 1 oa_version: Published Version project: - _id: 260C2330-B435-11E9-9278-68D0E5697425 call_identifier: H2020 grant_number: '754411' name: ISTplus - Postdoctoral Fellowships publication: Physical Review Fluids publication_status: published publisher: American Physical Society publist_id: '8038' pubrep_id: '1061' quality_controlled: '1' scopus_import: '1' status: public title: Drag enhancement and drag reduction in viscoelastic flow type: journal_article user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1 volume: 3 year: '2018' ... --- _id: '16' abstract: - lang: eng text: We report quantitative evidence of mixing-layer elastic instability in a viscoelastic fluid flow between two widely spaced obstacles hindering a channel flow at Re 1 and Wi 1. Two mixing layers with nonuniform shear velocity profiles are formed in the region between the obstacles. The mixing-layer instability arises in the vicinity of an inflection point on the shear velocity profile with a steep variation in the elastic stress. The instability results in an intermittent appearance of small vortices in the mixing layers and an amplification of spatiotemporal averaged vorticity in the elastic turbulence regime. The latter is characterized through scaling of friction factor with Wi and both pressure and velocity spectra. Furthermore, the observations reported provide improved understanding of the stability of the mixing layer in a viscoelastic fluid at large elasticity, i.e., Wi 1 and Re 1 and oppose the current view of suppression of vorticity solely by polymer additives. acknowledgement: This work was partially supported by the Israel Science Foundation (ISF; Grant No. 882/15) and the Binational USA-Israel Foundation (BSF; Grant No. 2016145). article_number: '103303' article_processing_charge: No article_type: original author: - first_name: Atul full_name: Varshney, Atul id: 2A2006B2-F248-11E8-B48F-1D18A9856A87 last_name: Varshney orcid: 0000-0002-3072-5999 - first_name: Victor full_name: Steinberg, Victor last_name: Steinberg citation: ama: Varshney A, Steinberg V. Mixing layer instability and vorticity amplification in a creeping viscoelastic flow. Physical Review Fluids. 2018;3(10). doi:10.1103/PhysRevFluids.3.103303 apa: Varshney, A., & Steinberg, V. (2018). Mixing layer instability and vorticity amplification in a creeping viscoelastic flow. Physical Review Fluids. American Physical Society. https://doi.org/10.1103/PhysRevFluids.3.103303 chicago: Varshney, Atul, and Victor Steinberg. “Mixing Layer Instability and Vorticity Amplification in a Creeping Viscoelastic Flow.” Physical Review Fluids. American Physical Society, 2018. https://doi.org/10.1103/PhysRevFluids.3.103303. ieee: A. Varshney and V. Steinberg, “Mixing layer instability and vorticity amplification in a creeping viscoelastic flow,” Physical Review Fluids, vol. 3, no. 10. American Physical Society, 2018. ista: Varshney A, Steinberg V. 2018. Mixing layer instability and vorticity amplification in a creeping viscoelastic flow. Physical Review Fluids. 3(10), 103303. mla: Varshney, Atul, and Victor Steinberg. “Mixing Layer Instability and Vorticity Amplification in a Creeping Viscoelastic Flow.” Physical Review Fluids, vol. 3, no. 10, 103303, American Physical Society, 2018, doi:10.1103/PhysRevFluids.3.103303. short: A. Varshney, V. Steinberg, Physical Review Fluids 3 (2018). date_created: 2018-12-11T11:44:10Z date_published: 2018-10-16T00:00:00Z date_updated: 2023-09-13T08:57:05Z day: '16' ddc: - '532' department: - _id: BjHo doi: 10.1103/PhysRevFluids.3.103303 ec_funded: 1 external_id: isi: - '000447469200001' file: - access_level: open_access checksum: 7fc0a2322214d1c04debef36d5bf2e8a content_type: application/pdf creator: system date_created: 2018-12-12T10:13:56Z date_updated: 2020-07-14T12:45:04Z file_id: '5043' file_name: IST-2018-1062-v1+1_PhysRevFluids.3.103303.pdf file_size: 1838431 relation: main_file file_date_updated: 2020-07-14T12:45:04Z has_accepted_license: '1' intvolume: ' 3' isi: 1 issue: '10' language: - iso: eng month: '10' oa: 1 oa_version: Submitted Version project: - _id: 260C2330-B435-11E9-9278-68D0E5697425 call_identifier: H2020 grant_number: '754411' name: ISTplus - Postdoctoral Fellowships publication: Physical Review Fluids publication_status: published publisher: American Physical Society publist_id: '8039' pubrep_id: '1062' quality_controlled: '1' scopus_import: '1' status: public title: Mixing layer instability and vorticity amplification in a creeping viscoelastic flow type: journal_article user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1 volume: 3 year: '2018' ... --- _id: '519' abstract: - lang: eng text: 'This study treats with the influence of a symmetry-breaking transversal magnetic field on the nonlinear dynamics of ferrofluidic Taylor-Couette flow – flow confined between two concentric independently rotating cylinders. We detected alternating ‘flip’ solutions which are flow states featuring typical characteristics of slow-fast-dynamics in dynamical systems. The flip corresponds to a temporal change in the axial wavenumber and we find them to appear either as pure 2-fold axisymmetric (due to the symmetry-breaking nature of the applied transversal magnetic field) or involving non-axisymmetric, helical modes in its interim solution. The latter ones show features of typical ribbon solutions. In any case the flip solutions have a preferential first axial wavenumber which corresponds to the more stable state (slow dynamics) and second axial wavenumber, corresponding to the short appearing more unstable state (fast dynamics). However, in both cases the flip time grows exponential with increasing the magnetic field strength before the flip solutions, living on 2-tori invariant manifolds, cease to exist, with lifetime going to infinity. Further we show that ferrofluidic flow turbulence differ from the classical, ordinary (usually at high Reynolds number) turbulence. The applied magnetic field hinders the free motion of ferrofluid partials and therefore smoothen typical turbulent quantities and features so that speaking of mildly chaotic dynamics seems to be a more appropriate expression for the observed motion. ' acknowledgement: S.Altmeyer is a Serra Húnter Fellow article_processing_charge: No article_type: original author: - first_name: Sebastian full_name: Altmeyer, Sebastian id: 2EE67FDC-F248-11E8-B48F-1D18A9856A87 last_name: Altmeyer orcid: 0000-0001-5964-0203 citation: ama: Altmeyer S. Non-linear dynamics and alternating ‘flip’ solutions in ferrofluidic Taylor-Couette flow. Journal of Magnetism and Magnetic Materials. 2018;452:427-441. doi:10.1016/j.jmmm.2017.12.073 apa: Altmeyer, S. (2018). Non-linear dynamics and alternating ‘flip’ solutions in ferrofluidic Taylor-Couette flow. Journal of Magnetism and Magnetic Materials. Elsevier. https://doi.org/10.1016/j.jmmm.2017.12.073 chicago: Altmeyer, Sebastian. “Non-Linear Dynamics and Alternating ‘Flip’ Solutions in Ferrofluidic Taylor-Couette Flow.” Journal of Magnetism and Magnetic Materials. Elsevier, 2018. https://doi.org/10.1016/j.jmmm.2017.12.073. ieee: S. Altmeyer, “Non-linear dynamics and alternating ‘flip’ solutions in ferrofluidic Taylor-Couette flow,” Journal of Magnetism and Magnetic Materials, vol. 452. Elsevier, pp. 427–441, 2018. ista: Altmeyer S. 2018. Non-linear dynamics and alternating ‘flip’ solutions in ferrofluidic Taylor-Couette flow. Journal of Magnetism and Magnetic Materials. 452, 427–441. mla: Altmeyer, Sebastian. “Non-Linear Dynamics and Alternating ‘Flip’ Solutions in Ferrofluidic Taylor-Couette Flow.” Journal of Magnetism and Magnetic Materials, vol. 452, Elsevier, 2018, pp. 427–41, doi:10.1016/j.jmmm.2017.12.073. short: S. Altmeyer, Journal of Magnetism and Magnetic Materials 452 (2018) 427–441. date_created: 2018-12-11T11:46:56Z date_published: 2018-04-15T00:00:00Z date_updated: 2023-09-13T09:03:44Z day: '15' ddc: - '530' department: - _id: BjHo doi: 10.1016/j.jmmm.2017.12.073 external_id: isi: - '000425547700061' file: - access_level: open_access checksum: 431f5cd4a628d7ca21161f82b14ccb4f content_type: application/pdf creator: dernst date_created: 2020-05-14T14:41:17Z date_updated: 2020-07-14T12:46:37Z file_id: '7838' file_name: 2018_Magnetism_Altmeyer.pdf file_size: 17309535 relation: main_file file_date_updated: 2020-07-14T12:46:37Z has_accepted_license: '1' intvolume: ' 452' isi: 1 language: - iso: eng month: '04' oa: 1 oa_version: Submitted Version page: 427 - 441 publication: Journal of Magnetism and Magnetic Materials publication_status: published publisher: Elsevier publist_id: '7297' quality_controlled: '1' scopus_import: '1' status: public title: Non-linear dynamics and alternating ‘flip’ solutions in ferrofluidic Taylor-Couette flow type: journal_article user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1 volume: 452 year: '2018' ... --- _id: '5996' abstract: - lang: eng text: 'In pipes, turbulence sets in despite the linear stability of the laminar Hagen–Poiseuille flow. The Reynolds number ( ) for which turbulence first appears in a given experiment – the ‘natural transition point’ – depends on imperfections of the set-up, or, more precisely, on the magnitude of finite amplitude perturbations. At onset, turbulence typically only occupies a certain fraction of the flow, and this fraction equally is found to differ from experiment to experiment. Despite these findings, Reynolds proposed that after sufficiently long times, flows may settle to steady conditions: below a critical velocity, flows should (regardless of initial conditions) always return to laminar, while above this velocity, eddying motion should persist. As will be shown, even in pipes several thousand diameters long, the spatio-temporal intermittent flow patterns observed at the end of the pipe strongly depend on the initial conditions, and there is no indication that different flow patterns would eventually settle to a (statistical) steady state. Exploiting the fact that turbulent puffs do not age (i.e. they are memoryless), we continuously recreate the puff sequence exiting the pipe at the pipe entrance, and in doing so introduce periodic boundary conditions for the puff pattern. This procedure allows us to study the evolution of the flow patterns for arbitrary long times, and we find that after times in excess of advective time units, indeed a statistical steady state is reached. Although the resulting flows remain spatio-temporally intermittent, puff splitting and decay rates eventually reach a balance, so that the turbulent fraction fluctuates around a well-defined level which only depends on . In accordance with Reynolds’ proposition, we find that at lower (here 2020), flows eventually always resume to laminar, while for higher ( ), turbulence persists. The critical point for pipe flow hence falls in the interval of $2020 , which is in very good agreement with the recently proposed value of . The latter estimate was based on single-puff statistics and entirely neglected puff interactions. Unlike in typical contact processes where such interactions strongly affect the percolation threshold, in pipe flow, the critical point is only marginally influenced. Interactions, on the other hand, are responsible for the approach to the statistical steady state. As shown, they strongly affect the resulting flow patterns, where they cause ‘puff clustering’, and these regions of large puff densities are observed to travel across the puff pattern in a wave-like fashion.' acknowledgement: ' We also thank Philipp Maier and the IST Austria workshop for theirdedicated technical support' article_processing_charge: No article_type: original author: - first_name: Mukund full_name: Vasudevan, Mukund id: 3C5A959A-F248-11E8-B48F-1D18A9856A87 last_name: Vasudevan - first_name: Björn full_name: Hof, Björn id: 3A374330-F248-11E8-B48F-1D18A9856A87 last_name: Hof orcid: 0000-0003-2057-2754 citation: ama: Vasudevan M, Hof B. The critical point of the transition to turbulence in pipe flow. Journal of Fluid Mechanics. 2018;839:76-94. doi:10.1017/jfm.2017.923 apa: Vasudevan, M., & Hof, B. (2018). The critical point of the transition to turbulence in pipe flow. Journal of Fluid Mechanics. Cambridge University Press. https://doi.org/10.1017/jfm.2017.923 chicago: Vasudevan, Mukund, and Björn Hof. “The Critical Point of the Transition to Turbulence in Pipe Flow.” Journal of Fluid Mechanics. Cambridge University Press, 2018. https://doi.org/10.1017/jfm.2017.923. ieee: M. Vasudevan and B. Hof, “The critical point of the transition to turbulence in pipe flow,” Journal of Fluid Mechanics, vol. 839. Cambridge University Press, pp. 76–94, 2018. ista: Vasudevan M, Hof B. 2018. The critical point of the transition to turbulence in pipe flow. Journal of Fluid Mechanics. 839, 76–94. mla: Vasudevan, Mukund, and Björn Hof. “The Critical Point of the Transition to Turbulence in Pipe Flow.” Journal of Fluid Mechanics, vol. 839, Cambridge University Press, 2018, pp. 76–94, doi:10.1017/jfm.2017.923. short: M. Vasudevan, B. Hof, Journal of Fluid Mechanics 839 (2018) 76–94. date_created: 2019-02-14T12:50:50Z date_published: 2018-03-25T00:00:00Z date_updated: 2023-09-19T14:37:49Z day: '25' department: - _id: BjHo doi: 10.1017/jfm.2017.923 ec_funded: 1 external_id: arxiv: - '1709.06372' isi: - '000437858300003' intvolume: ' 839' isi: 1 language: - iso: eng main_file_link: - open_access: '1' url: https://arxiv.org/abs/1709.06372 month: '03' oa: 1 oa_version: Preprint page: 76-94 project: - _id: 25152F3A-B435-11E9-9278-68D0E5697425 call_identifier: FP7 grant_number: '306589' name: Decoding the complexity of turbulence at its origin publication: Journal of Fluid Mechanics publication_identifier: eissn: - 1469-7645 issn: - 0022-1120 publication_status: published publisher: Cambridge University Press quality_controlled: '1' scopus_import: '1' status: public title: The critical point of the transition to turbulence in pipe flow type: journal_article user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1 volume: 839 year: '2018' ... --- _id: '328' abstract: - lang: eng text: The drag of turbulent flows can be drastically decreased by adding small amounts of high molecular weight polymers. While drag reduction initially increases with polymer concentration, it eventually saturates to what is known as the maximum drag reduction (MDR) asymptote; this asymptote is generally attributed to the dynamics being reduced to a marginal yet persistent state of subdued turbulent motion. Contrary to this accepted view, we show that, for an appropriate choice of parameters, polymers can reduce the drag beyond the suggested asymptotic limit, eliminating turbulence and giving way to laminar flow. At higher polymer concentrations, however, the laminar state becomes unstable, resulting in a fluctuating flow with the characteristic drag of the MDR asymptote. Our findings indicate that the asymptotic state is hence dynamically disconnected from ordinary turbulence. © 2018 American Physical Society. acknowledged_ssus: - _id: SSU acknowledgement: The authors thank Philipp Maier and the IST Austria workshop for their dedicated technical support. article_number: '124501' article_processing_charge: No author: - first_name: George H full_name: Choueiri, George H id: 448BD5BC-F248-11E8-B48F-1D18A9856A87 last_name: Choueiri - first_name: Jose M full_name: Lopez Alonso, Jose M id: 40770848-F248-11E8-B48F-1D18A9856A87 last_name: Lopez Alonso orcid: 0000-0002-0384-2022 - first_name: Björn full_name: Hof, Björn id: 3A374330-F248-11E8-B48F-1D18A9856A87 last_name: Hof orcid: 0000-0003-2057-2754 citation: ama: Choueiri GH, Lopez Alonso JM, Hof B. Exceeding the asymptotic limit of polymer drag reduction. Physical Review Letters. 2018;120(12). doi:10.1103/PhysRevLett.120.124501 apa: Choueiri, G. H., Lopez Alonso, J. M., & Hof, B. (2018). Exceeding the asymptotic limit of polymer drag reduction. Physical Review Letters. American Physical Society. https://doi.org/10.1103/PhysRevLett.120.124501 chicago: Choueiri, George H, Jose M Lopez Alonso, and Björn Hof. “Exceeding the Asymptotic Limit of Polymer Drag Reduction.” Physical Review Letters. American Physical Society, 2018. https://doi.org/10.1103/PhysRevLett.120.124501. ieee: G. H. Choueiri, J. M. Lopez Alonso, and B. Hof, “Exceeding the asymptotic limit of polymer drag reduction,” Physical Review Letters, vol. 120, no. 12. American Physical Society, 2018. ista: Choueiri GH, Lopez Alonso JM, Hof B. 2018. Exceeding the asymptotic limit of polymer drag reduction. Physical Review Letters. 120(12), 124501. mla: Choueiri, George H., et al. “Exceeding the Asymptotic Limit of Polymer Drag Reduction.” Physical Review Letters, vol. 120, no. 12, 124501, American Physical Society, 2018, doi:10.1103/PhysRevLett.120.124501. short: G.H. Choueiri, J.M. Lopez Alonso, B. Hof, Physical Review Letters 120 (2018). date_created: 2018-12-11T11:45:51Z date_published: 2018-03-19T00:00:00Z date_updated: 2023-10-10T13:27:44Z day: '19' department: - _id: BjHo doi: 10.1103/PhysRevLett.120.124501 ec_funded: 1 external_id: isi: - '000427804000005' intvolume: ' 120' isi: 1 issue: '12' language: - iso: eng main_file_link: - open_access: '1' url: https://arxiv.org/abs/1703.06271 month: '03' oa: 1 oa_version: Preprint project: - _id: 25681D80-B435-11E9-9278-68D0E5697425 call_identifier: FP7 grant_number: '291734' name: International IST Postdoc Fellowship Programme - _id: 25152F3A-B435-11E9-9278-68D0E5697425 call_identifier: FP7 grant_number: '306589' name: Decoding the complexity of turbulence at its origin publication: Physical Review Letters publication_status: published publisher: American Physical Society publist_id: '7537' quality_controlled: '1' scopus_import: '1' status: public title: Exceeding the asymptotic limit of polymer drag reduction type: journal_article user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87 volume: 120 year: '2018' ... --- _id: '136' abstract: - lang: eng text: Recent studies suggest that unstable, nonchaotic solutions of the Navier-Stokes equation may provide deep insights into fluid turbulence. In this article, we present a combined experimental and numerical study exploring the dynamical role of unstable equilibrium solutions and their invariant manifolds in a weakly turbulent, electromagnetically driven, shallow fluid layer. Identifying instants when turbulent evolution slows down, we compute 31 unstable equilibria of a realistic two-dimensional model of the flow. We establish the dynamical relevance of these unstable equilibria by showing that they are closely visited by the turbulent flow. We also establish the dynamical relevance of unstable manifolds by verifying that they are shadowed by turbulent trajectories departing from the neighborhoods of unstable equilibria over large distances in state space. article_processing_charge: No author: - first_name: Balachandra full_name: Suri, Balachandra id: 47A5E706-F248-11E8-B48F-1D18A9856A87 last_name: Suri - first_name: Jeffrey full_name: Tithof, Jeffrey last_name: Tithof - first_name: Roman full_name: Grigoriev, Roman last_name: Grigoriev - first_name: Michael full_name: Schatz, Michael last_name: Schatz citation: ama: Suri B, Tithof J, Grigoriev R, Schatz M. Unstable equilibria and invariant manifolds in quasi-two-dimensional Kolmogorov-like flow. Physical Review E. 2018;98(2). doi:10.1103/PhysRevE.98.023105 apa: Suri, B., Tithof, J., Grigoriev, R., & Schatz, M. (2018). Unstable equilibria and invariant manifolds in quasi-two-dimensional Kolmogorov-like flow. Physical Review E. American Physical Society. https://doi.org/10.1103/PhysRevE.98.023105 chicago: Suri, Balachandra, Jeffrey Tithof, Roman Grigoriev, and Michael Schatz. “Unstable Equilibria and Invariant Manifolds in Quasi-Two-Dimensional Kolmogorov-like Flow.” Physical Review E. American Physical Society, 2018. https://doi.org/10.1103/PhysRevE.98.023105. ieee: B. Suri, J. Tithof, R. Grigoriev, and M. Schatz, “Unstable equilibria and invariant manifolds in quasi-two-dimensional Kolmogorov-like flow,” Physical Review E, vol. 98, no. 2. American Physical Society, 2018. ista: Suri B, Tithof J, Grigoriev R, Schatz M. 2018. Unstable equilibria and invariant manifolds in quasi-two-dimensional Kolmogorov-like flow. Physical Review E. 98(2). mla: Suri, Balachandra, et al. “Unstable Equilibria and Invariant Manifolds in Quasi-Two-Dimensional Kolmogorov-like Flow.” Physical Review E, vol. 98, no. 2, American Physical Society, 2018, doi:10.1103/PhysRevE.98.023105. short: B. Suri, J. Tithof, R. Grigoriev, M. Schatz, Physical Review E 98 (2018). date_created: 2018-12-11T11:44:49Z date_published: 2018-08-13T00:00:00Z date_updated: 2023-10-10T13:29:10Z day: '13' department: - _id: BjHo doi: 10.1103/PhysRevE.98.023105 external_id: arxiv: - '1808.02088' isi: - '000441466800010' intvolume: ' 98' isi: 1 issue: '2' language: - iso: eng main_file_link: - open_access: '1' url: https://arxiv.org/abs/1808.02088 month: '08' oa: 1 oa_version: Submitted Version publication: Physical Review E publication_status: published publisher: American Physical Society quality_controlled: '1' scopus_import: '1' status: public title: Unstable equilibria and invariant manifolds in quasi-two-dimensional Kolmogorov-like flow type: journal_article user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87 volume: 98 year: '2018' ... --- _id: '422' abstract: - lang: eng text: We show that a rather simple, steady modification of the streamwise velocity profile in a pipe can lead to a complete collapse of turbulence and the flow fully relaminarizes. Two different devices, a stationary obstacle (inset) and a device which injects fluid through an annular gap close to the wall, are used to control the flow. Both devices modify the streamwise velocity profile such that the flow in the center of the pipe is decelerated and the flow in the near wall region is accelerated. We present measurements with stereoscopic particle image velocimetry to investigate and capture the development of the relaminarizing flow downstream these devices and the specific circumstances responsible for relaminarization. We find total relaminarization up to Reynolds numbers of 6000, where the skin friction in the far downstream distance is reduced by a factor of 3.4 due to relaminarization. In a smooth straight pipe the flow remains completely laminar downstream of the control. Furthermore, we show that transient (temporary) relaminarization in a spatially confined region right downstream the devices occurs also at much higher Reynolds numbers, accompanied by a significant local skin friction drag reduction. The underlying physical mechanism of relaminarization is attributed to a weakening of the near-wall turbulence production cycle. article_processing_charge: Yes (via OA deal) author: - first_name: Jakob full_name: Kühnen, Jakob id: 3A47AE32-F248-11E8-B48F-1D18A9856A87 last_name: Kühnen orcid: 0000-0003-4312-0179 - first_name: Davide full_name: Scarselli, Davide id: 40315C30-F248-11E8-B48F-1D18A9856A87 last_name: Scarselli orcid: 0000-0001-5227-4271 - first_name: Markus full_name: Schaner, Markus id: 316CE034-F248-11E8-B48F-1D18A9856A87 last_name: Schaner - first_name: Björn full_name: Hof, Björn id: 3A374330-F248-11E8-B48F-1D18A9856A87 last_name: Hof orcid: 0000-0003-2057-2754 citation: ama: Kühnen J, Scarselli D, Schaner M, Hof B. Relaminarization by steady modification of the streamwise velocity profile in a pipe. Flow Turbulence and Combustion. 2018;100(4):919-942. doi:10.1007/s10494-018-9896-4 apa: Kühnen, J., Scarselli, D., Schaner, M., & Hof, B. (2018). Relaminarization by steady modification of the streamwise velocity profile in a pipe. Flow Turbulence and Combustion. Springer. https://doi.org/10.1007/s10494-018-9896-4 chicago: Kühnen, Jakob, Davide Scarselli, Markus Schaner, and Björn Hof. “Relaminarization by Steady Modification of the Streamwise Velocity Profile in a Pipe.” Flow Turbulence and Combustion. Springer, 2018. https://doi.org/10.1007/s10494-018-9896-4. ieee: J. Kühnen, D. Scarselli, M. Schaner, and B. Hof, “Relaminarization by steady modification of the streamwise velocity profile in a pipe,” Flow Turbulence and Combustion, vol. 100, no. 4. Springer, pp. 919–942, 2018. ista: Kühnen J, Scarselli D, Schaner M, Hof B. 2018. Relaminarization by steady modification of the streamwise velocity profile in a pipe. Flow Turbulence and Combustion. 100(4), 919–942. mla: Kühnen, Jakob, et al. “Relaminarization by Steady Modification of the Streamwise Velocity Profile in a Pipe.” Flow Turbulence and Combustion, vol. 100, no. 4, Springer, 2018, pp. 919–42, doi:10.1007/s10494-018-9896-4. short: J. Kühnen, D. Scarselli, M. Schaner, B. Hof, Flow Turbulence and Combustion 100 (2018) 919–942. date_created: 2018-12-11T11:46:23Z date_published: 2018-01-01T00:00:00Z date_updated: 2024-03-27T23:30:36Z day: '01' ddc: - '530' department: - _id: BjHo doi: 10.1007/s10494-018-9896-4 ec_funded: 1 external_id: isi: - '000433113900004' file: - access_level: open_access checksum: d7c0bade150faabca150b0a9986e60ca content_type: application/pdf creator: dernst date_created: 2018-12-17T15:52:37Z date_updated: 2020-07-14T12:46:25Z file_id: '5717' file_name: 2018_FlowTurbulenceCombust_Kuehnen.pdf file_size: 2210020 relation: main_file file_date_updated: 2020-07-14T12:46:25Z has_accepted_license: '1' intvolume: ' 100' isi: 1 issue: '4' language: - iso: eng month: '01' oa: 1 oa_version: Published Version page: 919 - 942 project: - _id: 25152F3A-B435-11E9-9278-68D0E5697425 call_identifier: FP7 grant_number: '306589' name: Decoding the complexity of turbulence at its origin publication: Flow Turbulence and Combustion publication_status: published publisher: Springer publist_id: '7401' quality_controlled: '1' related_material: record: - id: '7258' relation: dissertation_contains status: public scopus_import: '1' status: public title: Relaminarization by steady modification of the streamwise velocity profile in a pipe tmp: image: /images/cc_by.png legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0) short: CC BY (4.0) type: journal_article user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1 volume: 100 year: '2018' ... --- _id: '461' abstract: - lang: eng text: Turbulence is the major cause of friction losses in transport processes and it is responsible for a drastic drag increase in flows over bounding surfaces. While much effort is invested into developing ways to control and reduce turbulence intensities, so far no methods exist to altogether eliminate turbulence if velocities are sufficiently large. We demonstrate for pipe flow that appropriate distortions to the velocity profile lead to a complete collapse of turbulence and subsequently friction losses are reduced by as much as 90%. Counterintuitively, the return to laminar motion is accomplished by initially increasing turbulence intensities or by transiently amplifying wall shear. Since neither the Reynolds number nor the shear stresses decrease (the latter often increase), these measures are not indicative of turbulence collapse. Instead, an amplification mechanism measuring the interaction between eddies and the mean shear is found to set a threshold below which turbulence is suppressed beyond recovery. acknowledgement: We acknowledge the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement 306589, the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 737549) and the Deutsche Forschungsgemeinschaft (Project No. FOR 1182) for financial support. We thank our technician P. Maier for providing highly valuable ideas and greatly supporting us in all technical aspects. We thank M. Schaner for technical drawings, construction and design. We thank M. Schwegel for a Matlab code to post-process experimental data. article_processing_charge: No author: - first_name: Jakob full_name: Kühnen, Jakob id: 3A47AE32-F248-11E8-B48F-1D18A9856A87 last_name: Kühnen orcid: 0000-0003-4312-0179 - first_name: Baofang full_name: Song, Baofang last_name: Song - first_name: Davide full_name: Scarselli, Davide id: 40315C30-F248-11E8-B48F-1D18A9856A87 last_name: Scarselli orcid: 0000-0001-5227-4271 - first_name: Nazmi B full_name: Budanur, Nazmi B id: 3EA1010E-F248-11E8-B48F-1D18A9856A87 last_name: Budanur orcid: 0000-0003-0423-5010 - first_name: Michael full_name: Riedl, Michael id: 3BE60946-F248-11E8-B48F-1D18A9856A87 last_name: Riedl orcid: 0000-0003-4844-6311 - first_name: Ashley full_name: Willis, Ashley last_name: Willis - first_name: Marc full_name: Avila, Marc last_name: Avila - first_name: Björn full_name: Hof, Björn id: 3A374330-F248-11E8-B48F-1D18A9856A87 last_name: Hof orcid: 0000-0003-2057-2754 citation: ama: Kühnen J, Song B, Scarselli D, et al. Destabilizing turbulence in pipe flow. Nature Physics. 2018;14:386-390. doi:10.1038/s41567-017-0018-3 apa: Kühnen, J., Song, B., Scarselli, D., Budanur, N. B., Riedl, M., Willis, A., … Hof, B. (2018). Destabilizing turbulence in pipe flow. Nature Physics. Nature Publishing Group. https://doi.org/10.1038/s41567-017-0018-3 chicago: Kühnen, Jakob, Baofang Song, Davide Scarselli, Nazmi B Budanur, Michael Riedl, Ashley Willis, Marc Avila, and Björn Hof. “Destabilizing Turbulence in Pipe Flow.” Nature Physics. Nature Publishing Group, 2018. https://doi.org/10.1038/s41567-017-0018-3. ieee: J. Kühnen et al., “Destabilizing turbulence in pipe flow,” Nature Physics, vol. 14. Nature Publishing Group, pp. 386–390, 2018. ista: Kühnen J, Song B, Scarselli D, Budanur NB, Riedl M, Willis A, Avila M, Hof B. 2018. Destabilizing turbulence in pipe flow. Nature Physics. 14, 386–390. mla: Kühnen, Jakob, et al. “Destabilizing Turbulence in Pipe Flow.” Nature Physics, vol. 14, Nature Publishing Group, 2018, pp. 386–90, doi:10.1038/s41567-017-0018-3. short: J. Kühnen, B. Song, D. Scarselli, N.B. Budanur, M. Riedl, A. Willis, M. Avila, B. Hof, Nature Physics 14 (2018) 386–390. date_created: 2018-12-11T11:46:36Z date_published: 2018-01-08T00:00:00Z date_updated: 2024-03-27T23:30:36Z day: '08' department: - _id: BjHo doi: 10.1038/s41567-017-0018-3 ec_funded: 1 external_id: isi: - '000429434100020' intvolume: ' 14' isi: 1 language: - iso: eng main_file_link: - open_access: '1' url: https://arxiv.org/abs/1711.06543 month: '01' oa: 1 oa_version: Preprint page: 386-390 project: - _id: 25152F3A-B435-11E9-9278-68D0E5697425 call_identifier: FP7 grant_number: '306589' name: Decoding the complexity of turbulence at its origin - _id: 25104D44-B435-11E9-9278-68D0E5697425 call_identifier: H2020 grant_number: '737549' name: Eliminating turbulence in oil pipelines publication: Nature Physics publication_status: published publisher: Nature Publishing Group publist_id: '7360' quality_controlled: '1' related_material: record: - id: '12726' relation: dissertation_contains status: public - id: '14530' relation: dissertation_contains status: public - id: '7258' relation: dissertation_contains status: public scopus_import: '1' status: public title: Destabilizing turbulence in pipe flow type: journal_article user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1 volume: 14 year: '2018' ... --- _id: '1211' abstract: - lang: eng text: Systems such as fluid flows in channels and pipes or the complex Ginzburg–Landau system, defined over periodic domains, exhibit both continuous symmetries, translational and rotational, as well as discrete symmetries under spatial reflections or complex conjugation. The simplest, and very common symmetry of this type is the equivariance of the defining equations under the orthogonal group O(2). We formulate a novel symmetry reduction scheme for such systems by combining the method of slices with invariant polynomial methods, and show how it works by applying it to the Kuramoto–Sivashinsky system in one spatial dimension. As an example, we track a relative periodic orbit through a sequence of bifurcations to the onset of chaos. Within the symmetry-reduced state space we are able to compute and visualize the unstable manifolds of relative periodic orbits, their torus bifurcations, a transition to chaos via torus breakdown, and heteroclinic connections between various relative periodic orbits. It would be very hard to carry through such analysis in the full state space, without a symmetry reduction such as the one we present here. acknowledgement: 'This work was supported by the family of late G. Robinson, Jr. and NSF Grant DMS-1211827. ' author: - first_name: Nazmi B full_name: Budanur, Nazmi B id: 3EA1010E-F248-11E8-B48F-1D18A9856A87 last_name: Budanur orcid: 0000-0003-0423-5010 - first_name: Predrag full_name: Cvitanović, Predrag last_name: Cvitanović citation: ama: Budanur NB, Cvitanović P. Unstable manifolds of relative periodic orbits in the symmetry reduced state space of the Kuramoto–Sivashinsky system. Journal of Statistical Physics. 2017;167(3-4):636-655. doi:10.1007/s10955-016-1672-z apa: Budanur, N. B., & Cvitanović, P. (2017). Unstable manifolds of relative periodic orbits in the symmetry reduced state space of the Kuramoto–Sivashinsky system. Journal of Statistical Physics. Springer. https://doi.org/10.1007/s10955-016-1672-z chicago: Budanur, Nazmi B, and Predrag Cvitanović. “Unstable Manifolds of Relative Periodic Orbits in the Symmetry Reduced State Space of the Kuramoto–Sivashinsky System.” Journal of Statistical Physics. Springer, 2017. https://doi.org/10.1007/s10955-016-1672-z. ieee: N. B. Budanur and P. Cvitanović, “Unstable manifolds of relative periodic orbits in the symmetry reduced state space of the Kuramoto–Sivashinsky system,” Journal of Statistical Physics, vol. 167, no. 3–4. Springer, pp. 636–655, 2017. ista: Budanur NB, Cvitanović P. 2017. Unstable manifolds of relative periodic orbits in the symmetry reduced state space of the Kuramoto–Sivashinsky system. Journal of Statistical Physics. 167(3–4), 636–655. mla: Budanur, Nazmi B., and Predrag Cvitanović. “Unstable Manifolds of Relative Periodic Orbits in the Symmetry Reduced State Space of the Kuramoto–Sivashinsky System.” Journal of Statistical Physics, vol. 167, no. 3–4, Springer, 2017, pp. 636–55, doi:10.1007/s10955-016-1672-z. short: N.B. Budanur, P. Cvitanović, Journal of Statistical Physics 167 (2017) 636–655. date_created: 2018-12-11T11:50:44Z date_published: 2017-05-01T00:00:00Z date_updated: 2021-01-12T06:49:07Z day: '01' ddc: - '530' department: - _id: BjHo doi: 10.1007/s10955-016-1672-z file: - access_level: open_access checksum: 3e971d09eb167761aa0888ed415b0056 content_type: application/pdf creator: system date_created: 2018-12-12T10:18:01Z date_updated: 2020-07-14T12:44:39Z file_id: '5319' file_name: IST-2017-782-v1+1_BudCvi15.pdf file_size: 2820207 relation: main_file file_date_updated: 2020-07-14T12:44:39Z has_accepted_license: '1' intvolume: ' 167' issue: 3-4 language: - iso: eng month: '05' oa: 1 oa_version: Submitted Version page: 636-655 publication: Journal of Statistical Physics publication_status: published publisher: Springer publist_id: '6136' pubrep_id: '782' quality_controlled: '1' scopus_import: 1 status: public title: Unstable manifolds of relative periodic orbits in the symmetry reduced state space of the Kuramoto–Sivashinsky system type: journal_article user_id: 3E5EF7F0-F248-11E8-B48F-1D18A9856A87 volume: 167 year: '2017' ...