--- _id: '5943' abstract: - lang: eng text: The hairpin instability of a jet in a crossflow (JICF) for a low jet-to-crossflow velocity ratio is investigated experimentally for a velocity ratio range of R ∈ (0.14, 0.75) and crossflow Reynolds numbers ReD ∈ (260, 640). From spectral analysis we characterize the Strouhal number and amplitude of the hairpin instability as a function of R and ReD. We demonstrate that the dynamics of the hairpins is well described by the Landau model, and, hence, that the instability occurs through Hopf bifurcation, similarly to other hydrodynamical oscillators such as wake behind different bluff bodies. Using the Landau model, we determine the precise threshold values of hairpin shedding. We also study the spatial dependence of this hydrodynamical instability, which shows a global behaviour. article_processing_charge: No article_type: original author: - first_name: Lukasz full_name: Klotz, Lukasz id: 2C9AF1C2-F248-11E8-B48F-1D18A9856A87 last_name: Klotz orcid: 0000-0003-1740-7635 - first_name: Konrad full_name: Gumowski, Konrad last_name: Gumowski - first_name: José Eduardo full_name: Wesfreid, José Eduardo last_name: Wesfreid citation: ama: Klotz L, Gumowski K, Wesfreid JE. Experiments on a jet in a crossflow in the low-velocity-ratio regime. Journal of Fluid Mechanics. 2019;863:386-406. doi:10.1017/jfm.2018.974 apa: Klotz, L., Gumowski, K., & Wesfreid, J. E. (2019). Experiments on a jet in a crossflow in the low-velocity-ratio regime. Journal of Fluid Mechanics. Cambridge University Press. https://doi.org/10.1017/jfm.2018.974 chicago: Klotz, Lukasz, Konrad Gumowski, and José Eduardo Wesfreid. “Experiments on a Jet in a Crossflow in the Low-Velocity-Ratio Regime.” Journal of Fluid Mechanics. Cambridge University Press, 2019. https://doi.org/10.1017/jfm.2018.974. ieee: L. Klotz, K. Gumowski, and J. E. Wesfreid, “Experiments on a jet in a crossflow in the low-velocity-ratio regime,” Journal of Fluid Mechanics, vol. 863. Cambridge University Press, pp. 386–406, 2019. ista: Klotz L, Gumowski K, Wesfreid JE. 2019. Experiments on a jet in a crossflow in the low-velocity-ratio regime. Journal of Fluid Mechanics. 863, 386–406. mla: Klotz, Lukasz, et al. “Experiments on a Jet in a Crossflow in the Low-Velocity-Ratio Regime.” Journal of Fluid Mechanics, vol. 863, Cambridge University Press, 2019, pp. 386–406, doi:10.1017/jfm.2018.974. short: L. Klotz, K. Gumowski, J.E. Wesfreid, Journal of Fluid Mechanics 863 (2019) 386–406. date_created: 2019-02-10T22:59:15Z date_published: 2019-03-25T00:00:00Z date_updated: 2023-08-24T14:43:13Z day: '25' department: - _id: BjHo doi: 10.1017/jfm.2018.974 ec_funded: 1 external_id: arxiv: - '1902.07931' isi: - '000526029100016' intvolume: ' 863' isi: 1 language: - iso: eng main_file_link: - open_access: '1' url: https://arxiv.org/abs/1902.07931 month: '03' oa: 1 oa_version: Preprint page: 386-406 project: - _id: 260C2330-B435-11E9-9278-68D0E5697425 call_identifier: H2020 grant_number: '754411' name: ISTplus - Postdoctoral Fellowships publication: Journal of Fluid Mechanics publication_status: published publisher: Cambridge University Press quality_controlled: '1' scopus_import: '1' status: public title: Experiments on a jet in a crossflow in the low-velocity-ratio regime type: journal_article user_id: 4359f0d1-fa6c-11eb-b949-802e58b17ae8 volume: 863 year: '2019' ... --- _id: '5878' abstract: - lang: eng text: We consider the motion of a droplet bouncing on a vibrating bath of the same fluid in the presence of a central potential. We formulate a rotation symmetry-reduced description of this system, which allows for the straightforward application of dynamical systems theory tools. As an illustration of the utility of the symmetry reduction, we apply it to a model of the pilot-wave system with a central harmonic force. We begin our analysis by identifying local bifurcations and the onset of chaos. We then describe the emergence of chaotic regions and their merging bifurcations, which lead to the formation of a global attractor. In this final regime, the droplet’s angular momentum spontaneously changes its sign as observed in the experiments of Perrard et al. article_number: '013122' article_processing_charge: No article_type: original 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: Marc full_name: Fleury, Marc last_name: Fleury citation: ama: 'Budanur NB, Fleury M. State space geometry of the chaotic pilot-wave hydrodynamics. Chaos: An Interdisciplinary Journal of Nonlinear Science. 2019;29(1). doi:10.1063/1.5058279' apa: 'Budanur, N. B., & Fleury, M. (2019). State space geometry of the chaotic pilot-wave hydrodynamics. Chaos: An Interdisciplinary Journal of Nonlinear Science. AIP Publishing. https://doi.org/10.1063/1.5058279' chicago: 'Budanur, Nazmi B, and Marc Fleury. “State Space Geometry of the Chaotic Pilot-Wave Hydrodynamics.” Chaos: An Interdisciplinary Journal of Nonlinear Science. AIP Publishing, 2019. https://doi.org/10.1063/1.5058279.' ieee: 'N. B. Budanur and M. Fleury, “State space geometry of the chaotic pilot-wave hydrodynamics,” Chaos: An Interdisciplinary Journal of Nonlinear Science, vol. 29, no. 1. AIP Publishing, 2019.' ista: 'Budanur NB, Fleury M. 2019. State space geometry of the chaotic pilot-wave hydrodynamics. Chaos: An Interdisciplinary Journal of Nonlinear Science. 29(1), 013122.' mla: 'Budanur, Nazmi B., and Marc Fleury. “State Space Geometry of the Chaotic Pilot-Wave Hydrodynamics.” Chaos: An Interdisciplinary Journal of Nonlinear Science, vol. 29, no. 1, 013122, AIP Publishing, 2019, doi:10.1063/1.5058279.' short: 'N.B. Budanur, M. Fleury, Chaos: An Interdisciplinary Journal of Nonlinear Science 29 (2019).' date_created: 2019-01-23T08:35:09Z date_published: 2019-01-22T00:00:00Z date_updated: 2023-08-25T10:16:11Z day: '22' department: - _id: BjHo doi: 10.1063/1.5058279 external_id: arxiv: - '1812.09011' isi: - '000457409100028' intvolume: ' 29' isi: 1 issue: '1' language: - iso: eng main_file_link: - open_access: '1' url: https://arxiv.org/abs/1812.09011 month: '01' oa: 1 oa_version: Preprint publication: 'Chaos: An Interdisciplinary Journal of Nonlinear Science' publication_identifier: eissn: - 1089-7682 issn: - 1054-1500 publication_status: published publisher: AIP Publishing quality_controlled: '1' related_material: link: - relation: erratum url: https://aip.scitation.org/doi/abs/10.1063/1.5097157 scopus_import: '1' status: public title: State space geometry of the chaotic pilot-wave hydrodynamics type: journal_article user_id: 4359f0d1-fa6c-11eb-b949-802e58b17ae8 volume: 29 year: '2019' ... --- _id: '6413' abstract: - lang: eng text: Phase-field methods have long been used to model the flow of immiscible fluids. Their ability to naturally capture interface topological changes is widely recognized, but their accuracy in simulating flows of real fluids in practical geometries is not established. We here quantitatively investigate the convergence of the phase-field method to the sharp-interface limit with simulations of two-phase pipe flow. We focus on core-annular flows, in which a highly viscous fluid is lubricated by a less viscous fluid, and validate our simulations with an analytic laminar solution, a formal linear stability analysis and also in the fully nonlinear regime. We demonstrate the ability of the phase-field method to accurately deal with non-rectangular geometry, strong advection, unsteady fluctuations and large viscosity contrast. We argue that phase-field methods are very promising for quantitatively studying moderately turbulent flows, especially at high concentrations of the disperse phase. article_processing_charge: No article_type: original author: - first_name: Baofang full_name: Song, Baofang last_name: Song - first_name: Carlos full_name: Plana, Carlos last_name: Plana - 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: Marc full_name: Avila, Marc last_name: Avila citation: ama: Song B, Plana C, Lopez Alonso JM, Avila M. Phase-field simulation of core-annular pipe flow. International Journal of Multiphase Flow. 2019;117:14-24. doi:10.1016/j.ijmultiphaseflow.2019.04.027 apa: Song, B., Plana, C., Lopez Alonso, J. M., & Avila, M. (2019). Phase-field simulation of core-annular pipe flow. International Journal of Multiphase Flow. Elsevier. https://doi.org/10.1016/j.ijmultiphaseflow.2019.04.027 chicago: Song, Baofang, Carlos Plana, Jose M Lopez Alonso, and Marc Avila. “Phase-Field Simulation of Core-Annular Pipe Flow.” International Journal of Multiphase Flow. Elsevier, 2019. https://doi.org/10.1016/j.ijmultiphaseflow.2019.04.027. ieee: B. Song, C. Plana, J. M. Lopez Alonso, and M. Avila, “Phase-field simulation of core-annular pipe flow,” International Journal of Multiphase Flow, vol. 117. Elsevier, pp. 14–24, 2019. ista: Song B, Plana C, Lopez Alonso JM, Avila M. 2019. Phase-field simulation of core-annular pipe flow. International Journal of Multiphase Flow. 117, 14–24. mla: Song, Baofang, et al. “Phase-Field Simulation of Core-Annular Pipe Flow.” International Journal of Multiphase Flow, vol. 117, Elsevier, 2019, pp. 14–24, doi:10.1016/j.ijmultiphaseflow.2019.04.027. short: B. Song, C. Plana, J.M. Lopez Alonso, M. Avila, International Journal of Multiphase Flow 117 (2019) 14–24. date_created: 2019-05-13T07:58:35Z date_published: 2019-08-01T00:00:00Z date_updated: 2023-08-25T10:19:55Z day: '01' department: - _id: BjHo doi: 10.1016/j.ijmultiphaseflow.2019.04.027 external_id: arxiv: - '1902.07351' isi: - '000474496000002' intvolume: ' 117' isi: 1 language: - iso: eng main_file_link: - open_access: '1' url: https://arxiv.org/abs/1902.07351 month: '08' oa: 1 oa_version: Preprint page: 14-24 publication: International Journal of Multiphase Flow publication_identifier: issn: - '03019322' publication_status: published publisher: Elsevier quality_controlled: '1' scopus_import: '1' status: public title: Phase-field simulation of core-annular pipe flow type: journal_article user_id: 4359f0d1-fa6c-11eb-b949-802e58b17ae8 volume: 117 year: '2019' ... --- _id: '6978' abstract: - lang: eng text: In pipes and channels, the onset of turbulence is initially dominated by localizedtransients, which lead to sustained turbulence through their collective dynamics. In thepresent work, we study numerically the localized turbulence in pipe flow and elucidate astate space structure that gives rise to transient chaos. Starting from the basin boundaryseparating laminar and turbulent flow, we identify transverse homoclinic orbits, thepresence of which necessitates a homoclinic tangle and chaos. A direct consequence ofthe homoclinic tangle is the fractal nature of the laminar-turbulent boundary, which wasconjectured in various earlier studies. By mapping the transverse intersections between thestable and unstable manifold of a periodic orbit, we identify the gateways that promote anescape from turbulence. acknowledged_ssus: - _id: ScienComp article_processing_charge: No article_type: original 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: Akshunna full_name: Dogra, Akshunna last_name: Dogra - 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, Dogra A, Hof B. Geometry of transient chaos in streamwise-localized pipe flow turbulence. Physical Review Fluids. 2019;4(10):102401. doi:10.1103/PhysRevFluids.4.102401 apa: Budanur, N. B., Dogra, A., & Hof, B. (2019). Geometry of transient chaos in streamwise-localized pipe flow turbulence. Physical Review Fluids. American Physical Society. https://doi.org/10.1103/PhysRevFluids.4.102401 chicago: Budanur, Nazmi B, Akshunna Dogra, and Björn Hof. “Geometry of Transient Chaos in Streamwise-Localized Pipe Flow Turbulence.” Physical Review Fluids. American Physical Society, 2019. https://doi.org/10.1103/PhysRevFluids.4.102401. ieee: N. B. Budanur, A. Dogra, and B. Hof, “Geometry of transient chaos in streamwise-localized pipe flow turbulence,” Physical Review Fluids, vol. 4, no. 10. American Physical Society, p. 102401, 2019. ista: Budanur NB, Dogra A, Hof B. 2019. Geometry of transient chaos in streamwise-localized pipe flow turbulence. Physical Review Fluids. 4(10), 102401. mla: Budanur, Nazmi B., et al. “Geometry of Transient Chaos in Streamwise-Localized Pipe Flow Turbulence.” Physical Review Fluids, vol. 4, no. 10, American Physical Society, 2019, p. 102401, doi:10.1103/PhysRevFluids.4.102401. short: N.B. Budanur, A. Dogra, B. Hof, Physical Review Fluids 4 (2019) 102401. date_created: 2019-11-04T10:04:01Z date_published: 2019-10-01T00:00:00Z date_updated: 2023-08-30T07:20:03Z day: '01' department: - _id: BjHo doi: 10.1103/PhysRevFluids.4.102401 external_id: arxiv: - '1810.02211' isi: - '000493510400001' intvolume: ' 4' isi: 1 issue: '10' language: - iso: eng main_file_link: - open_access: '1' url: https://arxiv.org/abs/1810.02211 month: '10' oa: 1 oa_version: Preprint page: '102401' publication: Physical Review Fluids publication_status: published publisher: American Physical Society quality_controlled: '1' scopus_import: '1' status: public title: Geometry of transient chaos in streamwise-localized pipe flow turbulence type: journal_article user_id: 4359f0d1-fa6c-11eb-b949-802e58b17ae8 volume: 4 year: '2019' ... --- _id: '7397' abstract: - lang: eng text: Polymer additives can substantially reduce the drag of turbulent flows and the upperlimit, the so called “maximum drag reduction” (MDR) asymptote is universal, i.e. inde-pendent of the type of polymer and solvent used. Until recently, the consensus was that,in this limit, flows are in a marginal state where only a minimal level of turbulence activ-ity persists. Observations in direct numerical simulations using minimal sized channelsappeared to support this view and reported long “hibernation” periods where turbu-lence is marginalized. In simulations of pipe flow we find that, indeed, with increasingWeissenberg number (Wi), turbulence expresses long periods of hibernation if the domainsize is small. However, with increasing pipe length, the temporal hibernation continuouslyalters to spatio-temporal intermittency and here the flow consists of turbulent puffs sur-rounded by laminar flow. Moreover, upon an increase in Wi, the flow fully relaminarises,in agreement with recent experiments. At even larger Wi, a different instability is en-countered causing a drag increase towards MDR. Our findings hence link earlier minimalflow unit simulations with recent experiments and confirm that the addition of polymersinitially suppresses Newtonian turbulence and leads to a reverse transition. The MDRstate on the other hand results from a separate instability and the underlying dynamicscorresponds to the recently proposed state of elasto-inertial-turbulence (EIT). article_processing_charge: No article_type: original author: - 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: George H full_name: Choueiri, George H id: 448BD5BC-F248-11E8-B48F-1D18A9856A87 last_name: Choueiri - first_name: Björn full_name: Hof, Björn id: 3A374330-F248-11E8-B48F-1D18A9856A87 last_name: Hof orcid: 0000-0003-2057-2754 citation: ama: Lopez Alonso JM, Choueiri GH, Hof B. Dynamics of viscoelastic pipe flow at low Reynolds numbers in the maximum drag reduction limit. Journal of Fluid Mechanics. 2019;874:699-719. doi:10.1017/jfm.2019.486 apa: Lopez Alonso, J. M., Choueiri, G. H., & Hof, B. (2019). Dynamics of viscoelastic pipe flow at low Reynolds numbers in the maximum drag reduction limit. Journal of Fluid Mechanics. CUP. https://doi.org/10.1017/jfm.2019.486 chicago: Lopez Alonso, Jose M, George H Choueiri, and Björn Hof. “Dynamics of Viscoelastic Pipe Flow at Low Reynolds Numbers in the Maximum Drag Reduction Limit.” Journal of Fluid Mechanics. CUP, 2019. https://doi.org/10.1017/jfm.2019.486. ieee: J. M. Lopez Alonso, G. H. Choueiri, and B. Hof, “Dynamics of viscoelastic pipe flow at low Reynolds numbers in the maximum drag reduction limit,” Journal of Fluid Mechanics, vol. 874. CUP, pp. 699–719, 2019. ista: Lopez Alonso JM, Choueiri GH, Hof B. 2019. Dynamics of viscoelastic pipe flow at low Reynolds numbers in the maximum drag reduction limit. Journal of Fluid Mechanics. 874, 699–719. mla: Lopez Alonso, Jose M., et al. “Dynamics of Viscoelastic Pipe Flow at Low Reynolds Numbers in the Maximum Drag Reduction Limit.” Journal of Fluid Mechanics, vol. 874, CUP, 2019, pp. 699–719, doi:10.1017/jfm.2019.486. short: J.M. Lopez Alonso, G.H. Choueiri, B. Hof, Journal of Fluid Mechanics 874 (2019) 699–719. date_created: 2020-01-29T16:05:19Z date_published: 2019-09-10T00:00:00Z date_updated: 2023-09-06T15:36:36Z day: '10' department: - _id: BjHo doi: 10.1017/jfm.2019.486 external_id: arxiv: - '1808.04080' isi: - '000475349900001' intvolume: ' 874' isi: 1 language: - iso: eng main_file_link: - open_access: '1' url: https://arxiv.org/abs/1808.04080 month: '09' oa: 1 oa_version: Preprint page: 699-719 publication: Journal of Fluid Mechanics publication_identifier: eissn: - 1469-7645 issn: - 0022-1120 publication_status: published publisher: CUP quality_controlled: '1' scopus_import: '1' status: public title: Dynamics of viscoelastic pipe flow at low Reynolds numbers in the maximum drag reduction limit type: journal_article user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1 volume: 874 year: '2019' ...