--- _id: '10299' abstract: - lang: eng text: Turbulence generally arises in shear flows if velocities and hence, inertial forces are sufficiently large. In striking contrast, viscoelastic fluids can exhibit disordered motion even at vanishing inertia. Intermediate between these cases, a state of chaotic motion, “elastoinertial turbulence” (EIT), has been observed in a narrow Reynolds number interval. We here determine the origin of EIT in experiments and show that characteristic EIT structures can be detected across an unexpectedly wide range of parameters. Close to onset, a pattern of chevron-shaped streaks emerges in qualitative agreement with linear and weakly nonlinear theory. However, in experiments, the dynamics remain weakly chaotic, and the instability can be traced to far lower Reynolds numbers than permitted by theory. For increasing inertia, the flow undergoes a transformation to a wall mode composed of inclined near-wall streaks and shear layers. This mode persists to what is known as the “maximum drag reduction limit,” and overall EIT is found to dominate viscoelastic flows across more than three orders of magnitude in Reynolds number. acknowledgement: We thank Y. Dubief, R. Kerswell, E. Marensi, V. Shankar, V. Steinberg, and V. Terrapon for discussions and helpful comments. A.V. and B.H. acknowledge funding from the Austrian Science Fund, grant I4188-N30, within the Deutsche Forschungsgemeinschaft research unit FOR 2688. article_number: e2102350118 article_processing_charge: No article_type: original 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: Atul full_name: Varshney, Atul id: 2A2006B2-F248-11E8-B48F-1D18A9856A87 last_name: Varshney orcid: 0000-0002-3072-5999 - first_name: Sarath full_name: Sankar, Sarath last_name: Sankar - 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, Varshney A, Sankar S, Hof B. Experimental observation of the origin and structure of elastoinertial turbulence. Proceedings of the National Academy of Sciences. 2021;118(45). doi:10.1073/pnas.2102350118 apa: Choueiri, G. H., Lopez Alonso, J. M., Varshney, A., Sankar, S., & Hof, B. (2021). Experimental observation of the origin and structure of elastoinertial turbulence. Proceedings of the National Academy of Sciences. National Academy of Sciences. https://doi.org/10.1073/pnas.2102350118 chicago: Choueiri, George H, Jose M Lopez Alonso, Atul Varshney, Sarath Sankar, and Björn Hof. “Experimental Observation of the Origin and Structure of Elastoinertial Turbulence.” Proceedings of the National Academy of Sciences. National Academy of Sciences, 2021. https://doi.org/10.1073/pnas.2102350118. ieee: G. H. Choueiri, J. M. Lopez Alonso, A. Varshney, S. Sankar, and B. Hof, “Experimental observation of the origin and structure of elastoinertial turbulence,” Proceedings of the National Academy of Sciences, vol. 118, no. 45. National Academy of Sciences, 2021. ista: Choueiri GH, Lopez Alonso JM, Varshney A, Sankar S, Hof B. 2021. Experimental observation of the origin and structure of elastoinertial turbulence. Proceedings of the National Academy of Sciences. 118(45), e2102350118. mla: Choueiri, George H., et al. “Experimental Observation of the Origin and Structure of Elastoinertial Turbulence.” Proceedings of the National Academy of Sciences, vol. 118, no. 45, e2102350118, National Academy of Sciences, 2021, doi:10.1073/pnas.2102350118. short: G.H. Choueiri, J.M. Lopez Alonso, A. Varshney, S. Sankar, B. Hof, Proceedings of the National Academy of Sciences 118 (2021). date_created: 2021-11-17T13:24:24Z date_published: 2021-11-03T00:00:00Z date_updated: 2023-08-14T11:50:10Z day: '03' department: - _id: BjHo doi: 10.1073/pnas.2102350118 external_id: arxiv: - '2103.00023' isi: - '000720926900019' pmid: - ' 34732570' intvolume: ' 118' isi: 1 issue: '45' keyword: - multidisciplinary - elastoinertial turbulence - viscoelastic flows - elastic instability - drag reduction language: - iso: eng main_file_link: - open_access: '1' url: https://arxiv.org/abs/2103.00023 month: '11' oa: 1 oa_version: Preprint pmid: 1 project: - _id: 238B8092-32DE-11EA-91FC-C7463DDC885E call_identifier: FWF grant_number: I04188 name: Instabilities in pulsating pipe flow of Newtonian and complex fluids publication: Proceedings of the National Academy of Sciences publication_identifier: eissn: - 1091-6490 issn: - 0027-8424 publication_status: published publisher: National Academy of Sciences quality_controlled: '1' scopus_import: '1' status: public title: Experimental observation of the origin and structure of elastoinertial turbulence type: journal_article user_id: 4359f0d1-fa6c-11eb-b949-802e58b17ae8 volume: 118 year: '2021' ... --- _id: '9728' abstract: - lang: eng text: "Most real-world flows are multiphase, yet we know little about them compared to their single-phase counterparts. Multiphase flows are more difficult to investigate as their dynamics occur in large parameter space and involve complex phenomena such as preferential concentration, turbulence modulation, non-Newtonian rheology, etc. Over the last few decades, experiments in particle-laden flows have taken a back seat in favour of ever-improving computational resources. However, computers are still not powerful enough to simulate a real-world fluid with millions of finite-size particles. Experiments are essential not only because they offer a reliable way to investigate real-world multiphase flows but also because they serve to validate numerical studies and steer the research in a relevant direction. In this work, we have experimentally investigated particle-laden flows in pipes, and in particular, examined the effect of particles on the laminar-turbulent transition and the drag scaling in turbulent flows.\r\n\r\nFor particle-laden pipe flows, an earlier study [Matas et al., 2003] reported how the sub-critical (i.e., hysteretic) transition that occurs via localised turbulent structures called puffs is affected by the addition of particles. In this study, in addition to this known transition, we found a super-critical transition to a globally fluctuating state with increasing particle concentration. At the same time, the Newtonian-type transition via puffs is delayed to larger Reynolds numbers. At an even higher concentration, only the globally fluctuating state is found. The dynamics of particle-laden flows are hence determined by two competing instabilities that give rise to three flow regimes: Newtonian-type turbulence at low, a particle-induced globally fluctuating state at high, and a coexistence state at intermediate concentrations.\r\n\r\nThe effect of particles on turbulent drag is ambiguous, with studies reporting drag reduction, no net change, and even drag increase. The ambiguity arises because, in addition to particle concentration, particle shape, size, and density also affect the net drag. Even similar particles might affect the flow dissimilarly in different Reynolds number and concentration ranges. In the present study, we explored a wide range of both Reynolds number and concentration, using spherical as well as cylindrical particles. We found that the spherical particles do not reduce drag while the cylindrical particles are drag-reducing within a specific Reynolds number interval. The interval strongly depends on the particle concentration and the relative size of the pipe and particles. Within this interval, the magnitude of drag reduction reaches a maximum. These drag reduction maxima appear to fall onto a distinct power-law curve irrespective of the pipe diameter and particle concentration, and this curve can be considered as the maximum drag reduction asymptote for a given fibre shape. Such an asymptote is well known for polymeric flows but had not been identified for particle-laden flows prior to this work." acknowledged_ssus: - _id: M-Shop alternative_title: - ISTA Thesis article_processing_charge: No author: - first_name: Nishchal full_name: Agrawal, Nishchal id: 469E6004-F248-11E8-B48F-1D18A9856A87 last_name: Agrawal citation: ama: Agrawal N. Transition to turbulence and drag reduction in particle-laden pipe flows. 2021. doi:10.15479/at:ista:9728 apa: Agrawal, N. (2021). Transition to turbulence and drag reduction in particle-laden pipe flows. Institute of Science and Technology Austria. https://doi.org/10.15479/at:ista:9728 chicago: Agrawal, Nishchal. “Transition to Turbulence and Drag Reduction in Particle-Laden Pipe Flows.” Institute of Science and Technology Austria, 2021. https://doi.org/10.15479/at:ista:9728. ieee: N. Agrawal, “Transition to turbulence and drag reduction in particle-laden pipe flows,” Institute of Science and Technology Austria, 2021. ista: Agrawal N. 2021. Transition to turbulence and drag reduction in particle-laden pipe flows. Institute of Science and Technology Austria. mla: Agrawal, Nishchal. Transition to Turbulence and Drag Reduction in Particle-Laden Pipe Flows. Institute of Science and Technology Austria, 2021, doi:10.15479/at:ista:9728. short: N. Agrawal, Transition to Turbulence and Drag Reduction in Particle-Laden Pipe Flows, Institute of Science and Technology Austria, 2021. date_created: 2021-07-27T13:40:30Z date_published: 2021-07-29T00:00:00Z date_updated: 2024-02-28T13:14:39Z day: '29' ddc: - '532' degree_awarded: PhD department: - _id: GradSch - _id: BjHo doi: 10.15479/at:ista:9728 file: - access_level: closed checksum: 77436be3563a90435024307b1b5ee7e8 content_type: application/x-zip-compressed creator: nagrawal date_created: 2021-07-28T13:32:02Z date_updated: 2022-07-29T22:30:05Z embargo_to: open_access file_id: '9744' file_name: Transition to Turbulence and Drag Reduction in Particle-Laden Pipe Flows.zip file_size: 22859658 relation: source_file - access_level: open_access checksum: 72a891d7daba85445c29b868c22575ed content_type: application/pdf creator: nagrawal date_created: 2021-07-28T13:32:05Z date_updated: 2022-07-29T22:30:05Z embargo: 2022-07-28 file_id: '9745' file_name: Transition to Turbulence and Drag Reduction in Particle-Laden Pipe Flows.pdf file_size: 18658048 relation: main_file file_date_updated: 2022-07-29T22:30:05Z has_accepted_license: '1' keyword: - Drag Reduction - Transition to Turbulence - Multiphase Flows - particle Laden Flows - Complex Flows - Experiments - Fluid Dynamics language: - iso: eng license: https://creativecommons.org/licenses/by/4.0/ month: '07' oa: 1 oa_version: Published Version page: '118' publication_identifier: issn: - 2663-337X publication_status: published publisher: Institute of Science and Technology Austria related_material: record: - id: '6189' relation: part_of_dissertation status: public status: public supervisor: - first_name: Björn full_name: Hof, Björn id: 3A374330-F248-11E8-B48F-1D18A9856A87 last_name: Hof orcid: 0000-0003-2057-2754 title: Transition to turbulence and drag reduction in particle-laden pipe flows 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: dissertation user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1 year: '2021' ... --- _id: '7364' abstract: - lang: eng text: We present nsCouette, a highly scalable software tool to solve the Navier–Stokes equations for incompressible fluid flow between differentially heated and independently rotating, concentric cylinders. It is based on a pseudospectral spatial discretization and dynamic time-stepping. It is implemented in modern Fortran with a hybrid MPI-OpenMP parallelization scheme and thus designed to compute turbulent flows at high Reynolds and Rayleigh numbers. An additional GPU implementation (C-CUDA) for intermediate problem sizes and a version for pipe flow (nsPipe) are also provided. article_number: '100395' 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: Daniel full_name: Feldmann, Daniel last_name: Feldmann - first_name: Markus full_name: Rampp, Markus last_name: Rampp - first_name: Alberto full_name: Vela-Martín, Alberto last_name: Vela-Martín - first_name: Liang full_name: Shi, Liang id: 374A3F1A-F248-11E8-B48F-1D18A9856A87 last_name: Shi - first_name: Marc full_name: Avila, Marc last_name: Avila citation: ama: Lopez Alonso JM, Feldmann D, Rampp M, Vela-Martín A, Shi L, Avila M. nsCouette – A high-performance code for direct numerical simulations of turbulent Taylor–Couette flow. SoftwareX. 2020;11. doi:10.1016/j.softx.2019.100395 apa: Lopez Alonso, J. M., Feldmann, D., Rampp, M., Vela-Martín, A., Shi, L., & Avila, M. (2020). nsCouette – A high-performance code for direct numerical simulations of turbulent Taylor–Couette flow. SoftwareX. Elsevier. https://doi.org/10.1016/j.softx.2019.100395 chicago: Lopez Alonso, Jose M, Daniel Feldmann, Markus Rampp, Alberto Vela-Martín, Liang Shi, and Marc Avila. “NsCouette – A High-Performance Code for Direct Numerical Simulations of Turbulent Taylor–Couette Flow.” SoftwareX. Elsevier, 2020. https://doi.org/10.1016/j.softx.2019.100395. ieee: J. M. Lopez Alonso, D. Feldmann, M. Rampp, A. Vela-Martín, L. Shi, and M. Avila, “nsCouette – A high-performance code for direct numerical simulations of turbulent Taylor–Couette flow,” SoftwareX, vol. 11. Elsevier, 2020. ista: Lopez Alonso JM, Feldmann D, Rampp M, Vela-Martín A, Shi L, Avila M. 2020. nsCouette – A high-performance code for direct numerical simulations of turbulent Taylor–Couette flow. SoftwareX. 11, 100395. mla: Lopez Alonso, Jose M., et al. “NsCouette – A High-Performance Code for Direct Numerical Simulations of Turbulent Taylor–Couette Flow.” SoftwareX, vol. 11, 100395, Elsevier, 2020, doi:10.1016/j.softx.2019.100395. short: J.M. Lopez Alonso, D. Feldmann, M. Rampp, A. Vela-Martín, L. Shi, M. Avila, SoftwareX 11 (2020). date_created: 2020-01-26T23:00:35Z date_published: 2020-01-17T00:00:00Z date_updated: 2023-08-17T14:29:59Z day: '17' ddc: - '000' department: - _id: BjHo doi: 10.1016/j.softx.2019.100395 external_id: arxiv: - '1908.00587' isi: - '000552271200011' file: - access_level: open_access checksum: 2af1a1a3cc33557b345145276f221668 content_type: application/pdf creator: dernst date_created: 2020-01-27T07:32:46Z date_updated: 2020-07-14T12:47:56Z file_id: '7365' file_name: 2020_SoftwareX_Lopez.pdf file_size: 679707 relation: main_file file_date_updated: 2020-07-14T12:47:56Z has_accepted_license: '1' intvolume: ' 11' isi: 1 language: - iso: eng license: https://creativecommons.org/licenses/by-nc-nd/4.0/ month: '01' oa: 1 oa_version: Published Version publication: SoftwareX publication_identifier: eissn: - '23527110' publication_status: published publisher: Elsevier quality_controlled: '1' scopus_import: '1' status: public title: nsCouette – A high-performance code for direct numerical simulations of turbulent Taylor–Couette flow tmp: image: /images/cc_by_nc_nd.png legal_code_url: https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode name: Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) short: CC BY-NC-ND (4.0) type: journal_article user_id: 4359f0d1-fa6c-11eb-b949-802e58b17ae8 volume: 11 year: '2020' ... --- _id: '7534' abstract: - lang: eng text: 'In the past two decades, our understanding of the transition to turbulence in shear flows with linearly stable laminar solutions has greatly improved. Regarding the susceptibility of the laminar flow, two concepts have been particularly useful: the edge states and the minimal seeds. In this nonlinear picture of the transition, the basin boundary of turbulence is set by the edge state''s stable manifold and this manifold comes closest in energy to the laminar equilibrium at the minimal seed. We begin this paper by presenting numerical experiments in which three-dimensional perturbations are too energetic to trigger turbulence in pipe flow but they do lead to turbulence when their amplitude is reduced. We show that this seemingly counterintuitive observation is in fact consistent with the fully nonlinear description of the transition mediated by the edge state. In order to understand the physical mechanisms behind this process, we measure the turbulent kinetic energy production and dissipation rates as a function of the radial coordinate. Our main observation is that the transition to turbulence relies on the energy amplification away from the wall, as opposed to the turbulence itself, whose energy is predominantly produced near the wall. This observation is further supported by the similar analyses on the minimal seeds and the edge states. Furthermore, we show that the time evolution of production-over-dissipation curves provides a clear distinction between the different initial amplification stages of the transition to turbulence from the minimal seed.' article_number: '023903' 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: Elena full_name: Marensi, Elena last_name: Marensi - first_name: Ashley P. full_name: Willis, Ashley P. last_name: Willis - 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, Marensi E, Willis AP, Hof B. Upper edge of chaos and the energetics of transition in pipe flow. Physical Review Fluids. 2020;5(2). doi:10.1103/physrevfluids.5.023903 apa: Budanur, N. B., Marensi, E., Willis, A. P., & Hof, B. (2020). Upper edge of chaos and the energetics of transition in pipe flow. Physical Review Fluids. American Physical Society. https://doi.org/10.1103/physrevfluids.5.023903 chicago: Budanur, Nazmi B, Elena Marensi, Ashley P. Willis, and Björn Hof. “Upper Edge of Chaos and the Energetics of Transition in Pipe Flow.” Physical Review Fluids. American Physical Society, 2020. https://doi.org/10.1103/physrevfluids.5.023903. ieee: N. B. Budanur, E. Marensi, A. P. Willis, and B. Hof, “Upper edge of chaos and the energetics of transition in pipe flow,” Physical Review Fluids, vol. 5, no. 2. American Physical Society, 2020. ista: Budanur NB, Marensi E, Willis AP, Hof B. 2020. Upper edge of chaos and the energetics of transition in pipe flow. Physical Review Fluids. 5(2), 023903. mla: Budanur, Nazmi B., et al. “Upper Edge of Chaos and the Energetics of Transition in Pipe Flow.” Physical Review Fluids, vol. 5, no. 2, 023903, American Physical Society, 2020, doi:10.1103/physrevfluids.5.023903. short: N.B. Budanur, E. Marensi, A.P. Willis, B. Hof, Physical Review Fluids 5 (2020). date_created: 2020-02-27T10:26:57Z date_published: 2020-02-21T00:00:00Z date_updated: 2023-08-18T06:44:46Z day: '21' department: - _id: BjHo doi: 10.1103/physrevfluids.5.023903 external_id: arxiv: - '1912.09270' isi: - '000515065100001' intvolume: ' 5' isi: 1 issue: '2' language: - iso: eng main_file_link: - open_access: '1' url: https://arxiv.org/abs/1912.09270 month: '02' oa: 1 oa_version: Preprint publication: Physical Review Fluids publication_identifier: issn: - 2469-990X publication_status: published publisher: American Physical Society quality_controlled: '1' scopus_import: '1' status: public title: Upper edge of chaos and the energetics of transition in pipe flow type: journal_article user_id: 4359f0d1-fa6c-11eb-b949-802e58b17ae8 volume: 5 year: '2020' ... --- _id: '7563' abstract: - lang: eng text: "We introduce “state space persistence analysis” for deducing the symbolic dynamics of time series data obtained from high-dimensional chaotic attractors. To this end, we adapt a topological data analysis technique known as persistent homology for the characterization of state space projections of chaotic trajectories and periodic orbits. By comparing the shapes along a chaotic trajectory to those of the periodic orbits, state space persistence analysis quantifies the shape similarity of chaotic trajectory segments and periodic orbits. We demonstrate the method by applying it to the three-dimensional Rössler system and a 30-dimensional discretization of the Kuramoto–Sivashinsky partial differential equation in (1+1) dimensions.\r\nOne way of studying chaotic attractors systematically is through their symbolic dynamics, in which one partitions the state space into qualitatively different regions and assigns a symbol to each such region.1–3 This yields a “coarse-grained” state space of the system, which can then be reduced to a Markov chain encoding all possible transitions between the states of the system. While it is possible to obtain the symbolic dynamics of low-dimensional chaotic systems with standard tools such as Poincaré maps, when applied to high-dimensional systems such as turbulent flows, these tools alone are not sufficient to determine symbolic dynamics.4,5 In this paper, we develop “state space persistence analysis” and demonstrate that it can be utilized to infer the symbolic dynamics in very high-dimensional settings." article_number: '033109' article_processing_charge: No article_type: original author: - first_name: Gökhan full_name: Yalniz, Gökhan id: 66E74FA2-D8BF-11E9-8249-8DE2E5697425 last_name: Yalniz orcid: 0000-0002-8490-9312 - first_name: Nazmi B full_name: Budanur, Nazmi B id: 3EA1010E-F248-11E8-B48F-1D18A9856A87 last_name: Budanur orcid: 0000-0003-0423-5010 citation: ama: Yalniz G, Budanur NB. Inferring symbolic dynamics of chaotic flows from persistence. Chaos. 2020;30(3). doi:10.1063/1.5122969 apa: Yalniz, G., & Budanur, N. B. (2020). Inferring symbolic dynamics of chaotic flows from persistence. Chaos. AIP Publishing. https://doi.org/10.1063/1.5122969 chicago: Yalniz, Gökhan, and Nazmi B Budanur. “Inferring Symbolic Dynamics of Chaotic Flows from Persistence.” Chaos. AIP Publishing, 2020. https://doi.org/10.1063/1.5122969. ieee: G. Yalniz and N. B. Budanur, “Inferring symbolic dynamics of chaotic flows from persistence,” Chaos, vol. 30, no. 3. AIP Publishing, 2020. ista: Yalniz G, Budanur NB. 2020. Inferring symbolic dynamics of chaotic flows from persistence. Chaos. 30(3), 033109. mla: Yalniz, Gökhan, and Nazmi B. Budanur. “Inferring Symbolic Dynamics of Chaotic Flows from Persistence.” Chaos, vol. 30, no. 3, 033109, AIP Publishing, 2020, doi:10.1063/1.5122969. short: G. Yalniz, N.B. Budanur, Chaos 30 (2020). date_created: 2020-03-04T08:06:25Z date_published: 2020-03-03T00:00:00Z date_updated: 2023-08-18T06:47:16Z day: '03' department: - _id: BjHo doi: 10.1063/1.5122969 external_id: arxiv: - '1910.04584' isi: - '000519254800002' intvolume: ' 30' isi: 1 issue: '3' language: - iso: eng main_file_link: - open_access: '1' url: https://doi.org/10.1063/1.5122969 month: '03' oa: 1 oa_version: Published Version publication: Chaos publication_identifier: eissn: - 1089-7682 issn: - 1054-1500 publication_status: published publisher: AIP Publishing quality_controlled: '1' scopus_import: '1' status: public title: Inferring symbolic dynamics of chaotic flows from persistence type: journal_article user_id: 4359f0d1-fa6c-11eb-b949-802e58b17ae8 volume: 30 year: '2020' ... --- _id: '8043' abstract: - lang: eng text: With decreasing Reynolds number, Re, turbulence in channel flow becomes spatio-temporally intermittent and self-organises into solitary stripes oblique to the mean flow direction. We report here the existence of localised nonlinear travelling wave solutions of the Navier–Stokes equations possessing this obliqueness property. Such solutions are identified numerically using edge tracking coupled with arclength continuation. All solutions emerge in saddle-node bifurcations at values of Re lower than the non-localised solutions. Relative periodic orbit solutions bifurcating from branches of travelling waves have also been computed. A complete parametric study is performed, including their stability, the investigation of their large-scale flow, and the robustness to changes of the numerical domain. acknowledgement: The authors thank S. Zammert and B. Budanur for useful discussions. J. F. Gibson is gratefully acknowledged for the development and the maintenance of the code Channelflow. Y.D. would like to thank P. Schlatter and D. S. Henningson for an early collaboration on a similar topic in the case of plane Couette flow during the years 2008–2013. article_number: A7 article_processing_charge: Yes (via OA deal) article_type: original author: - first_name: Chaitanya S full_name: Paranjape, Chaitanya S id: 3D85B7C4-F248-11E8-B48F-1D18A9856A87 last_name: Paranjape - first_name: Yohann full_name: Duguet, Yohann last_name: Duguet - first_name: Björn full_name: Hof, Björn id: 3A374330-F248-11E8-B48F-1D18A9856A87 last_name: Hof orcid: 0000-0003-2057-2754 citation: ama: Paranjape CS, Duguet Y, Hof B. Oblique stripe solutions of channel flow. Journal of Fluid Mechanics. 2020;897. doi:10.1017/jfm.2020.322 apa: Paranjape, C. S., Duguet, Y., & Hof, B. (2020). Oblique stripe solutions of channel flow. Journal of Fluid Mechanics. Cambridge University Press. https://doi.org/10.1017/jfm.2020.322 chicago: Paranjape, Chaitanya S, Yohann Duguet, and Björn Hof. “Oblique Stripe Solutions of Channel Flow.” Journal of Fluid Mechanics. Cambridge University Press, 2020. https://doi.org/10.1017/jfm.2020.322. ieee: C. S. Paranjape, Y. Duguet, and B. Hof, “Oblique stripe solutions of channel flow,” Journal of Fluid Mechanics, vol. 897. Cambridge University Press, 2020. ista: Paranjape CS, Duguet Y, Hof B. 2020. Oblique stripe solutions of channel flow. Journal of Fluid Mechanics. 897, A7. mla: Paranjape, Chaitanya S., et al. “Oblique Stripe Solutions of Channel Flow.” Journal of Fluid Mechanics, vol. 897, A7, Cambridge University Press, 2020, doi:10.1017/jfm.2020.322. short: C.S. Paranjape, Y. Duguet, B. Hof, Journal of Fluid Mechanics 897 (2020). date_created: 2020-06-29T07:59:35Z date_published: 2020-08-25T00:00:00Z date_updated: 2023-08-22T07:48:02Z day: '25' ddc: - '530' department: - _id: BjHo doi: 10.1017/jfm.2020.322 external_id: isi: - '000539132300001' file: - access_level: open_access checksum: 3f487bf6d9286787096306eaa18702e8 content_type: application/pdf creator: cziletti date_created: 2020-06-30T08:37:37Z date_updated: 2020-07-14T12:48:08Z file_id: '8070' file_name: 2020_JournalOfFluidMech_Paranjape.pdf file_size: 767873 relation: main_file file_date_updated: 2020-07-14T12:48:08Z has_accepted_license: '1' intvolume: ' 897' isi: 1 language: - iso: eng license: https://creativecommons.org/licenses/by-nc-sa/4.0/ month: '08' oa: 1 oa_version: Published Version publication: Journal of Fluid Mechanics publication_identifier: eissn: - '14697645' issn: - '00221120' publication_status: published publisher: Cambridge University Press quality_controlled: '1' scopus_import: '1' status: public title: Oblique stripe solutions of channel flow tmp: image: /images/cc_by_nc_sa.png legal_code_url: https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode name: Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) short: CC BY-NC-SA (4.0) type: journal_article user_id: 4359f0d1-fa6c-11eb-b949-802e58b17ae8 volume: 897 year: '2020' ... --- _id: '8634' abstract: - lang: eng text: In laboratory studies and numerical simulations, we observe clear signatures of unstable time-periodic solutions in a moderately turbulent quasi-two-dimensional flow. We validate the dynamical relevance of such solutions by demonstrating that turbulent flows in both experiment and numerics transiently display time-periodic dynamics when they shadow unstable periodic orbits (UPOs). We show that UPOs we computed are also statistically significant, with turbulent flows spending a sizable fraction of the total time near these solutions. As a result, the average rates of energy input and dissipation for the turbulent flow and frequently visited UPOs differ only by a few percent. acknowledgement: M. F. S. and R. O. G. acknowledge funding from the National Science Foundation (CMMI-1234436, DMS1125302, CMMI-1725587) and Defense Advanced Research Projects Agency (HR0011-16-2-0033). B. S.has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7/2007–2013/ under REA Grant Agreement No. 291734. article_number: '064501' article_processing_charge: No article_type: original author: - first_name: Balachandra full_name: Suri, Balachandra id: 47A5E706-F248-11E8-B48F-1D18A9856A87 last_name: Suri - first_name: Logan full_name: Kageorge, Logan last_name: Kageorge - first_name: Roman O. full_name: Grigoriev, Roman O. last_name: Grigoriev - first_name: Michael F. full_name: Schatz, Michael F. last_name: Schatz citation: ama: Suri B, Kageorge L, Grigoriev RO, Schatz MF. Capturing turbulent dynamics and statistics in experiments with unstable periodic orbits. Physical Review Letters. 2020;125(6). doi:10.1103/physrevlett.125.064501 apa: Suri, B., Kageorge, L., Grigoriev, R. O., & Schatz, M. F. (2020). Capturing turbulent dynamics and statistics in experiments with unstable periodic orbits. Physical Review Letters. American Physical Society. https://doi.org/10.1103/physrevlett.125.064501 chicago: Suri, Balachandra, Logan Kageorge, Roman O. Grigoriev, and Michael F. Schatz. “Capturing Turbulent Dynamics and Statistics in Experiments with Unstable Periodic Orbits.” Physical Review Letters. American Physical Society, 2020. https://doi.org/10.1103/physrevlett.125.064501. ieee: B. Suri, L. Kageorge, R. O. Grigoriev, and M. F. Schatz, “Capturing turbulent dynamics and statistics in experiments with unstable periodic orbits,” Physical Review Letters, vol. 125, no. 6. American Physical Society, 2020. ista: Suri B, Kageorge L, Grigoriev RO, Schatz MF. 2020. Capturing turbulent dynamics and statistics in experiments with unstable periodic orbits. Physical Review Letters. 125(6), 064501. mla: Suri, Balachandra, et al. “Capturing Turbulent Dynamics and Statistics in Experiments with Unstable Periodic Orbits.” Physical Review Letters, vol. 125, no. 6, 064501, American Physical Society, 2020, doi:10.1103/physrevlett.125.064501. short: B. Suri, L. Kageorge, R.O. Grigoriev, M.F. Schatz, Physical Review Letters 125 (2020). date_created: 2020-10-08T17:27:32Z date_published: 2020-08-05T00:00:00Z date_updated: 2023-09-05T12:08:29Z day: '05' department: - _id: BjHo doi: 10.1103/physrevlett.125.064501 ec_funded: 1 external_id: arxiv: - '2008.02367' isi: - '000555785600005' intvolume: ' 125' isi: 1 issue: '6' keyword: - General Physics and Astronomy language: - iso: eng main_file_link: - open_access: '1' url: https://arxiv.org/abs/2008.02367 month: '08' oa: 1 oa_version: Preprint project: - _id: 25681D80-B435-11E9-9278-68D0E5697425 call_identifier: FP7 grant_number: '291734' name: International IST Postdoc Fellowship Programme publication: Physical Review Letters publication_identifier: eissn: - 1079-7114 issn: - 0031-9007 publication_status: published publisher: American Physical Society quality_controlled: '1' status: public title: Capturing turbulent dynamics and statistics in experiments with unstable periodic orbits type: journal_article user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1 volume: 125 year: '2020' ... --- _id: '7932' abstract: - lang: eng text: Pulsating flows through tubular geometries are laminar provided that velocities are moderate. This in particular is also believed to apply to cardiovascular flows where inertial forces are typically too low to sustain turbulence. On the other hand, flow instabilities and fluctuating shear stresses are held responsible for a variety of cardiovascular diseases. Here we report a nonlinear instability mechanism for pulsating pipe flow that gives rise to bursts of turbulence at low flow rates. Geometrical distortions of small, yet finite, amplitude are found to excite a state consisting of helical vortices during flow deceleration. The resulting flow pattern grows rapidly in magnitude, breaks down into turbulence, and eventually returns to laminar when the flow accelerates. This scenario causes shear stress fluctuations and flow reversal during each pulsation cycle. Such unsteady conditions can adversely affect blood vessels and have been shown to promote inflammation and dysfunction of the shear stress-sensitive endothelial cell layer. article_processing_charge: No article_type: original author: - first_name: Duo full_name: Xu, Duo id: 3454D55E-F248-11E8-B48F-1D18A9856A87 last_name: Xu - first_name: Atul full_name: Varshney, Atul id: 2A2006B2-F248-11E8-B48F-1D18A9856A87 last_name: Varshney orcid: 0000-0002-3072-5999 - first_name: Xingyu full_name: Ma, Xingyu id: 34BADBA6-F248-11E8-B48F-1D18A9856A87 last_name: Ma orcid: 0000-0002-0179-9737 - first_name: Baofang full_name: Song, Baofang last_name: Song - first_name: Michael full_name: Riedl, Michael id: 3BE60946-F248-11E8-B48F-1D18A9856A87 last_name: Riedl orcid: 0000-0003-4844-6311 - 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: Xu D, Varshney A, Ma X, et al. Nonlinear hydrodynamic instability and turbulence in pulsatile flow. Proceedings of the National Academy of Sciences of the United States of America. 2020;117(21):11233-11239. doi:10.1073/pnas.1913716117 apa: Xu, D., Varshney, A., Ma, X., Song, B., Riedl, M., Avila, M., & Hof, B. (2020). Nonlinear hydrodynamic instability and turbulence in pulsatile flow. Proceedings of the National Academy of Sciences of the United States of America. National Academy of Sciences. https://doi.org/10.1073/pnas.1913716117 chicago: Xu, Duo, Atul Varshney, Xingyu Ma, Baofang Song, Michael Riedl, Marc Avila, and Björn Hof. “Nonlinear Hydrodynamic Instability and Turbulence in Pulsatile Flow.” Proceedings of the National Academy of Sciences of the United States of America. National Academy of Sciences, 2020. https://doi.org/10.1073/pnas.1913716117. ieee: D. Xu et al., “Nonlinear hydrodynamic instability and turbulence in pulsatile flow,” Proceedings of the National Academy of Sciences of the United States of America, vol. 117, no. 21. National Academy of Sciences, pp. 11233–11239, 2020. ista: Xu D, Varshney A, Ma X, Song B, Riedl M, Avila M, Hof B. 2020. Nonlinear hydrodynamic instability and turbulence in pulsatile flow. Proceedings of the National Academy of Sciences of the United States of America. 117(21), 11233–11239. mla: Xu, Duo, et al. “Nonlinear Hydrodynamic Instability and Turbulence in Pulsatile Flow.” Proceedings of the National Academy of Sciences of the United States of America, vol. 117, no. 21, National Academy of Sciences, 2020, pp. 11233–39, doi:10.1073/pnas.1913716117. short: D. Xu, A. Varshney, X. Ma, B. Song, M. Riedl, M. Avila, B. Hof, Proceedings of the National Academy of Sciences of the United States of America 117 (2020) 11233–11239. date_created: 2020-06-07T22:00:51Z date_published: 2020-05-26T00:00:00Z date_updated: 2023-11-30T10:55:13Z day: '26' department: - _id: BjHo doi: 10.1073/pnas.1913716117 ec_funded: 1 external_id: arxiv: - '2005.11190' isi: - '000536797100014' intvolume: ' 117' isi: 1 issue: '21' language: - iso: eng main_file_link: - open_access: '1' url: https://arxiv.org/abs/2005.11190 month: '05' oa: 1 oa_version: Preprint page: 11233-11239 project: - _id: 238B8092-32DE-11EA-91FC-C7463DDC885E call_identifier: FWF grant_number: I04188 name: Instabilities in pulsating pipe flow of Newtonian and complex fluids - _id: 260C2330-B435-11E9-9278-68D0E5697425 call_identifier: H2020 grant_number: '754411' name: ISTplus - Postdoctoral Fellowships publication: Proceedings of the National Academy of Sciences of the United States of America publication_identifier: eissn: - '10916490' issn: - '00278424' publication_status: published publisher: National Academy of Sciences quality_controlled: '1' related_material: link: - description: News on IST Homepage relation: press_release url: https://ist.ac.at/en/news/blood-flows-more-turbulent-than-previously-expected/ record: - id: '12726' relation: dissertation_contains status: public - id: '14530' relation: dissertation_contains status: public scopus_import: '1' status: public title: Nonlinear hydrodynamic instability and turbulence in pulsatile flow type: journal_article user_id: 4359f0d1-fa6c-11eb-b949-802e58b17ae8 volume: 117 year: '2020' ... --- _id: '7258' abstract: - lang: eng text: Many flows encountered in nature and applications are characterized by a chaotic motion known as turbulence. Turbulent flows generate intense friction with pipe walls and are responsible for considerable amounts of energy losses at world scale. The nature of turbulent friction and techniques aimed at reducing it have been subject of extensive research over the last century, but no definite answer has been found yet. In this thesis we show that in pipes at moderate turbulent Reynolds numbers friction is better described by the power law first introduced by Blasius and not by the Prandtl–von Kármán formula. At higher Reynolds numbers, large scale motions gradually become more important in the flow and can be related to the change in scaling of friction. Next, we present a series of new techniques that can relaminarize turbulence by suppressing a key mechanism that regenerates it at walls, the lift–up effect. In addition, we investigate the process of turbulence decay in several experiments and discuss the drag reduction potential. Finally, we examine the behavior of friction under pulsating conditions inspired by the human heart cycle and we show that under such circumstances turbulent friction can be reduced to produce energy savings. alternative_title: - ISTA Thesis article_processing_charge: No author: - first_name: Davide full_name: Scarselli, Davide id: 40315C30-F248-11E8-B48F-1D18A9856A87 last_name: Scarselli orcid: 0000-0001-5227-4271 citation: ama: Scarselli D. New approaches to reduce friction in turbulent pipe flow. 2020. doi:10.15479/AT:ISTA:7258 apa: Scarselli, D. (2020). New approaches to reduce friction in turbulent pipe flow. Institute of Science and Technology Austria. https://doi.org/10.15479/AT:ISTA:7258 chicago: Scarselli, Davide. “New Approaches to Reduce Friction in Turbulent Pipe Flow.” Institute of Science and Technology Austria, 2020. https://doi.org/10.15479/AT:ISTA:7258. ieee: D. Scarselli, “New approaches to reduce friction in turbulent pipe flow,” Institute of Science and Technology Austria, 2020. ista: Scarselli D. 2020. New approaches to reduce friction in turbulent pipe flow. Institute of Science and Technology Austria. mla: Scarselli, Davide. New Approaches to Reduce Friction in Turbulent Pipe Flow. Institute of Science and Technology Austria, 2020, doi:10.15479/AT:ISTA:7258. short: D. Scarselli, New Approaches to Reduce Friction in Turbulent Pipe Flow, Institute of Science and Technology Austria, 2020. date_created: 2020-01-12T16:07:26Z date_published: 2020-01-13T00:00:00Z date_updated: 2023-09-15T12:20:08Z day: '13' ddc: - '532' degree_awarded: PhD department: - _id: BjHo doi: 10.15479/AT:ISTA:7258 ec_funded: 1 file: - access_level: closed checksum: 4df1ab24e9896635106adde5a54615bf content_type: application/zip creator: dscarsel date_created: 2020-01-12T15:57:14Z date_updated: 2021-01-13T23:30:05Z embargo_to: open_access file_id: '7259' file_name: 2020_Scarselli_Thesis.zip file_size: 26640830 relation: source_file - access_level: open_access checksum: 48659ab98e3414293c7a721385c2fd1c content_type: application/pdf creator: dscarsel date_created: 2020-01-12T15:56:14Z date_updated: 2021-01-13T23:30:05Z embargo: 2021-01-12 file_id: '7260' file_name: 2020_Scarselli_Thesis.pdf file_size: 8515844 relation: main_file file_date_updated: 2021-01-13T23:30:05Z has_accepted_license: '1' language: - iso: eng month: '01' oa: 1 oa_version: None page: '174' 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 - _id: 25136C54-B435-11E9-9278-68D0E5697425 grant_number: HO 4393/1-2 name: Experimental studies of the turbulence transition and transport processes in turbulent Taylor-Couette currents publication_identifier: issn: - 2663-337X publication_status: published publisher: Institute of Science and Technology Austria related_material: record: - id: '6228' relation: part_of_dissertation status: public - id: '6486' relation: part_of_dissertation status: public - id: '461' relation: part_of_dissertation status: public - id: '422' relation: part_of_dissertation status: public status: public supervisor: - first_name: Björn full_name: Hof, Björn id: 3A374330-F248-11E8-B48F-1D18A9856A87 last_name: Hof orcid: 0000-0003-2057-2754 title: New approaches to reduce friction in turbulent pipe flow type: dissertation user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1 year: '2020' ... --- _id: '8350' abstract: - lang: eng text: "Cytoplasm is a gel-like crowded environment composed of tens of thousands of macromolecules, organelles, cytoskeletal networks and cytosol. The structure of the cytoplasm is thought to be highly organized and heterogeneous due to the crowding of its constituents and their effective compartmentalization. In such an environment, the diffusive dynamics of the molecules is very restricted, an effect that is further amplified by clustering and anchoring of molecules. Despite the jammed nature of the cytoplasm at the microscopic scale, large-scale reorganization of cytoplasm is essential for important cellular functions, such as nuclear positioning and cell division. How such mesoscale reorganization of the cytoplasm is achieved, especially for very large cells such as oocytes or syncytial tissues that can span hundreds of micrometers in size, has only begun to be understood.\r\nIn this thesis, I focus on the recent advances in elucidating the molecular, cellular and biophysical principles underlying cytoplasmic organization across different scales, structures and species. First, I outline which of these principles have been identified by reductionist approaches, such as in vitro reconstitution assays, where boundary conditions and components can be modulated at ease. I then describe how the theoretical and experimental framework established in these reduced systems have been applied to their more complex in vivo counterparts, in particular oocytes and embryonic syncytial structures, and discuss how such complex biological systems can initiate symmetry breaking and establish patterning.\r\nSpecifically, I examine an example of large-scale reorganizations taking place in zebrafish embryos, where extensive cytoplasmic streaming leads to the segregation of cytoplasm from yolk granules along the animal-vegetal axis of the embryo. Using biophysical experimentation and theory, I investigate the forces underlying this process, to show that this process does not rely on cortical actin reorganization, as previously thought, but instead on a cell-cycle-dependent bulk actin polymerization wave traveling from the animal to the vegetal pole of the embryo. This wave functions in segregation by both pulling cytoplasm animally and pushing yolk granules vegetally. Cytoplasm pulling is mediated by bulk actin network flows exerting friction forces on the cytoplasm, while yolk granule pushing is achieved by a mechanism closely resembling actin comet formation on yolk granules. This study defines a novel role of bulk actin polymerization waves in embryo polarization via cytoplasmic segregation. Lastly, I describe the cytoplasmic reorganizations taking place during zebrafish oocyte maturation, where the initial segregation of the cytoplasm and yolk granules occurs. Here, I demonstrate a previously uncharacterized wave of microtubule aster formation, traveling the oocyte along the animal-vegetal axis. Further research is required to determine the role of such microtubule structures in cytoplasmic reorganizations therein.\r\nCollectively, these studies provide further evidence for the coupling between cell cytoskeleton and cell cycle machinery, which can underlie a core self-organizing mechanism for orchestrating large-scale reorganizations in a cell-cycle-tunable manner, where the modulations of the force-generating machinery and cytoplasmic mechanics can be harbored to fulfill cellular functions." acknowledged_ssus: - _id: PreCl - _id: Bio - _id: EM-Fac acknowledgement: "I would have had no fish and hence no results without our wonderful fish facility crew, Verena Mayer, Eva Schlegl, Andreas Mlak and Matthias Nowak. Special thanks to Verena for being always happy to help and dealing with our chaotic schedules in the lab. Danke auch, Verena, für deine Geduld, mit mir auf Deutsch zu sprechen. Das hat mir sehr geholfen.\r\nSpecial thanks to the Bioimaging and EM facilities at IST Austria for supporting us every day. Very special thanks would go to Robert Hauschild for his continuous support on data analysis and also to Jack Merrin for designing and building microfabricated chambers for the project and for the various discussions on making zebrafish extracts." alternative_title: - ISTA Thesis article_processing_charge: No author: - first_name: Shayan full_name: Shamipour, Shayan id: 40B34FE2-F248-11E8-B48F-1D18A9856A87 last_name: Shamipour citation: ama: Shamipour S. Bulk actin dynamics drive phase segregation in zebrafish oocytes . 2020. doi:10.15479/AT:ISTA:8350 apa: Shamipour, S. (2020). Bulk actin dynamics drive phase segregation in zebrafish oocytes . Institute of Science and Technology Austria. https://doi.org/10.15479/AT:ISTA:8350 chicago: Shamipour, Shayan. “Bulk Actin Dynamics Drive Phase Segregation in Zebrafish Oocytes .” Institute of Science and Technology Austria, 2020. https://doi.org/10.15479/AT:ISTA:8350. ieee: S. Shamipour, “Bulk actin dynamics drive phase segregation in zebrafish oocytes ,” Institute of Science and Technology Austria, 2020. ista: Shamipour S. 2020. Bulk actin dynamics drive phase segregation in zebrafish oocytes . Institute of Science and Technology Austria. mla: Shamipour, Shayan. Bulk Actin Dynamics Drive Phase Segregation in Zebrafish Oocytes . Institute of Science and Technology Austria, 2020, doi:10.15479/AT:ISTA:8350. short: S. Shamipour, Bulk Actin Dynamics Drive Phase Segregation in Zebrafish Oocytes , Institute of Science and Technology Austria, 2020. date_created: 2020-09-09T11:12:10Z date_published: 2020-09-09T00:00:00Z date_updated: 2023-09-27T14:16:45Z day: '09' ddc: - '570' degree_awarded: PhD department: - _id: BjHo - _id: CaHe doi: 10.15479/AT:ISTA:8350 file: - access_level: closed checksum: 6e47871c74f85008b9876112eb3fcfa1 content_type: application/vnd.openxmlformats-officedocument.wordprocessingml.document creator: sshamip date_created: 2020-09-09T11:06:27Z date_updated: 2021-09-11T22:30:05Z embargo_to: open_access file_id: '8351' file_name: Shayan-Thesis-Final.docx file_size: 65194814 relation: source_file - access_level: open_access checksum: 1b44c57f04d7e8a6fe41b1c9c55a52a3 content_type: application/pdf creator: sshamip date_created: 2020-09-09T11:06:13Z date_updated: 2021-09-11T22:30:05Z embargo: 2021-09-10 file_id: '8352' file_name: Shayan-Thesis-Final.pdf file_size: 23729605 relation: main_file file_date_updated: 2021-09-11T22:30:05Z has_accepted_license: '1' language: - iso: eng month: '09' oa: 1 oa_version: None page: '107' publication_identifier: issn: - 2663-337X publication_status: published publisher: Institute of Science and Technology Austria related_material: record: - id: '661' relation: part_of_dissertation status: public - id: '6508' relation: part_of_dissertation status: public - id: '7001' relation: part_of_dissertation status: public - id: '735' relation: part_of_dissertation status: public status: public supervisor: - first_name: Carl-Philipp J full_name: Heisenberg, Carl-Philipp J id: 39427864-F248-11E8-B48F-1D18A9856A87 last_name: Heisenberg orcid: 0000-0002-0912-4566 - first_name: Björn full_name: Hof, Björn id: 3A374330-F248-11E8-B48F-1D18A9856A87 last_name: Hof orcid: 0000-0003-2057-2754 title: 'Bulk actin dynamics drive phase segregation in zebrafish oocytes ' type: dissertation user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1 year: '2020' ...