[{"article_processing_charge":"Yes (via OA deal)","date_created":"2023-10-30T09:32:28Z","department":[{"_id":"GradSch"},{"_id":"BjHo"}],"publication_status":"published","intvolume":"       974","title":"Dynamics and proliferation of turbulent stripes in plane-Poiseuille and plane-Couette flows","_id":"14466","author":[{"id":"0BE7553A-1004-11EA-B805-18983DDC885E","first_name":"Elena","last_name":"Marensi","orcid":"0000-0001-7173-4923","full_name":"Marensi, Elena"},{"first_name":"Gökhan","last_name":"Yalniz","orcid":"0000-0002-8490-9312","full_name":"Yalniz, Gökhan","id":"66E74FA2-D8BF-11E9-8249-8DE2E5697425"},{"id":"3A374330-F248-11E8-B48F-1D18A9856A87","last_name":"Hof","first_name":"Björn","full_name":"Hof, Björn","orcid":"0000-0003-2057-2754"}],"publisher":"Cambridge University Press","article_type":"original","quality_controlled":"1","file_date_updated":"2024-02-15T09:05:21Z","day":"10","arxiv":1,"doi":"10.1017/jfm.2023.780","abstract":[{"lang":"eng","text":"The first long-lived turbulent structures observable in planar shear flows take the form of localized stripes, inclined with respect to the mean flow direction. The dynamics of these stripes is central to transition, and recent studies proposed an analogy to directed percolation where the stripes’ proliferation is ultimately responsible for the turbulence becoming sustained. In the present study we focus on the internal stripe dynamics as well as on the eventual stripe expansion, and we compare the underlying mechanisms in pressure- and shear-driven planar flows, respectively, plane-Poiseuille and plane-Couette flow. Despite the similarities of the overall laminar–turbulence patterns, the stripe proliferation processes in the two cases are fundamentally different. Starting from the growth and sustenance of individual stripes, we find that in plane-Couette flow new streaks are created stochastically throughout the stripe whereas in plane-Poiseuille flow streak creation is deterministic and occurs locally at the downstream tip. Because of the up/downstream symmetry, Couette stripes, in contrast to Poiseuille stripes, have two weak and two strong laminar turbulent interfaces. These differences in symmetry as well as in internal growth give rise to two fundamentally different stripe splitting mechanisms. In plane-Poiseuille flow splitting is connected to the elongational growth of the original stripe, and it results from a break-off/shedding of the stripe's tail. In plane-Couette flow splitting follows from a broadening of the original stripe and a division along the stripe into two slimmer stripes."}],"citation":{"ista":"Marensi E, Yalniz G, Hof B. 2023. Dynamics and proliferation of turbulent stripes in plane-Poiseuille and plane-Couette flows. Journal of Fluid Mechanics. 974, A21.","mla":"Marensi, Elena, et al. “Dynamics and Proliferation of Turbulent Stripes in Plane-Poiseuille and Plane-Couette Flows.” <i>Journal of Fluid Mechanics</i>, vol. 974, A21, Cambridge University Press, 2023, doi:<a href=\"https://doi.org/10.1017/jfm.2023.780\">10.1017/jfm.2023.780</a>.","short":"E. Marensi, G. Yalniz, B. Hof, Journal of Fluid Mechanics 974 (2023).","chicago":"Marensi, Elena, Gökhan Yalniz, and Björn Hof. “Dynamics and Proliferation of Turbulent Stripes in Plane-Poiseuille and Plane-Couette Flows.” <i>Journal of Fluid Mechanics</i>. Cambridge University Press, 2023. <a href=\"https://doi.org/10.1017/jfm.2023.780\">https://doi.org/10.1017/jfm.2023.780</a>.","ieee":"E. Marensi, G. Yalniz, and B. Hof, “Dynamics and proliferation of turbulent stripes in plane-Poiseuille and plane-Couette flows,” <i>Journal of Fluid Mechanics</i>, vol. 974. Cambridge University Press, 2023.","apa":"Marensi, E., Yalniz, G., &#38; Hof, B. (2023). Dynamics and proliferation of turbulent stripes in plane-Poiseuille and plane-Couette flows. <i>Journal of Fluid Mechanics</i>. Cambridge University Press. <a href=\"https://doi.org/10.1017/jfm.2023.780\">https://doi.org/10.1017/jfm.2023.780</a>","ama":"Marensi E, Yalniz G, Hof B. Dynamics and proliferation of turbulent stripes in plane-Poiseuille and plane-Couette flows. <i>Journal of Fluid Mechanics</i>. 2023;974. doi:<a href=\"https://doi.org/10.1017/jfm.2023.780\">10.1017/jfm.2023.780</a>"},"year":"2023","date_updated":"2024-02-15T09:06:23Z","external_id":{"isi":["001088363700001"],"arxiv":["2212.12406"]},"isi":1,"volume":974,"acknowledgement":"E.M. acknowledges funding from the ISTplus fellowship programme. G.Y. and B.H. acknowledge a grant from the Simons Foundation (662960, BH).","ddc":["530"],"project":[{"_id":"238598C6-32DE-11EA-91FC-C7463DDC885E","grant_number":"662960","name":"Revisiting the Turbulence Problem Using Statistical Mechanics: Experimental Studies on Transitional and Turbulent Flows"}],"oa_version":"Published Version","article_number":"A21","month":"11","has_accepted_license":"1","publication":"Journal of Fluid Mechanics","keyword":["turbulence","transition to turbulence","patterns"],"language":[{"iso":"eng"}],"publication_identifier":{"eissn":["1469-7645"],"issn":["0022-1120"]},"oa":1,"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","short":"CC BY (4.0)","image":"/images/cc_by.png","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)"},"type":"journal_article","date_published":"2023-11-10T00:00:00Z","file":[{"access_level":"open_access","success":1,"relation":"main_file","creator":"dernst","file_id":"14996","checksum":"17c64c1fb0d5f73252364bf98b0b9e1a","file_size":2804641,"date_created":"2024-02-15T09:05:21Z","file_name":"2023_JourFluidMechanics_Marensi.pdf","content_type":"application/pdf","date_updated":"2024-02-15T09:05:21Z"}],"user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","status":"public"},{"type":"journal_article","date_published":"2021-02-08T00:00:00Z","oa":1,"publication_identifier":{"eissn":["1432-0746"],"issn":["0004-6361"]},"status":"public","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","main_file_link":[{"open_access":"1","url":"https://arxiv.org/abs/2006.10660"}],"publication":"Astronomy & Astrophysics","article_number":"A64","month":"02","oa_version":"Preprint","keyword":["Space and Planetary Science","Astronomy and Astrophysics","hydrodynamics / turbulence / stars","rotation / stars","evolution"],"language":[{"iso":"eng"}],"external_id":{"arxiv":["2006.10660"]},"citation":{"apa":"Park, J., Prat, V., Mathis, S., &#38; Bugnet, L. A. (2021). Horizontal shear instabilities in rotating stellar radiation zones: II. Effects of the full Coriolis acceleration. <i>Astronomy &#38; Astrophysics</i>. EDP Sciences. <a href=\"https://doi.org/10.1051/0004-6361/202038654\">https://doi.org/10.1051/0004-6361/202038654</a>","ama":"Park J, Prat V, Mathis S, Bugnet LA. Horizontal shear instabilities in rotating stellar radiation zones: II. Effects of the full Coriolis acceleration. <i>Astronomy &#38; Astrophysics</i>. 2021;646. doi:<a href=\"https://doi.org/10.1051/0004-6361/202038654\">10.1051/0004-6361/202038654</a>","chicago":"Park, J., V. Prat, S. Mathis, and Lisa Annabelle Bugnet. “Horizontal Shear Instabilities in Rotating Stellar Radiation Zones: II. Effects of the Full Coriolis Acceleration.” <i>Astronomy &#38; Astrophysics</i>. EDP Sciences, 2021. <a href=\"https://doi.org/10.1051/0004-6361/202038654\">https://doi.org/10.1051/0004-6361/202038654</a>.","ieee":"J. Park, V. Prat, S. Mathis, and L. A. Bugnet, “Horizontal shear instabilities in rotating stellar radiation zones: II. Effects of the full Coriolis acceleration,” <i>Astronomy &#38; Astrophysics</i>, vol. 646. EDP Sciences, 2021.","short":"J. Park, V. Prat, S. Mathis, L.A. Bugnet, Astronomy &#38; Astrophysics 646 (2021).","mla":"Park, J., et al. “Horizontal Shear Instabilities in Rotating Stellar Radiation Zones: II. Effects of the Full Coriolis Acceleration.” <i>Astronomy &#38; Astrophysics</i>, vol. 646, A64, EDP Sciences, 2021, doi:<a href=\"https://doi.org/10.1051/0004-6361/202038654\">10.1051/0004-6361/202038654</a>.","ista":"Park J, Prat V, Mathis S, Bugnet LA. 2021. Horizontal shear instabilities in rotating stellar radiation zones: II. Effects of the full Coriolis acceleration. Astronomy &#38; Astrophysics. 646, A64."},"year":"2021","date_updated":"2022-08-19T10:18:03Z","abstract":[{"text":"Context. Stellar interiors are the seat of efficient transport of angular momentum all along their evolution. In this context, understanding the dependence of the turbulent transport triggered by the instabilities of the vertical and horizontal shears of the differential rotation in stellar radiation zones as a function of their rotation, stratification, and thermal diffusivity is mandatory. Indeed, it constitutes one of the cornerstones of the rotational transport and mixing theory, which is implemented in stellar evolution codes to predict the rotational and chemical evolutions of stars.\r\n\r\nAims. We investigate horizontal shear instabilities in rotating stellar radiation zones by considering the full Coriolis acceleration with both the dimensionless horizontal Coriolis component f̃ and the vertical component f.\r\n\r\nMethods. We performed a linear stability analysis using linearized equations derived from the Navier-Stokes and heat transport equations in the rotating nontraditional f-plane. We considered a horizontal shear flow with a hyperbolic tangent profile as the base flow. The linear stability was analyzed numerically in wide ranges of parameters, and we performed an asymptotic analysis for large vertical wavenumbers using the Wentzel-Kramers-Brillouin-Jeffreys (WKBJ) approximation for nondiffusive and highly-diffusive fluids.\r\n\r\nResults. As in the traditional f-plane approximation, we identify two types of instabilities: the inflectional and inertial instabilities. The inflectional instability is destabilized as f̃ increases and its maximum growth rate increases significantly, while the thermal diffusivity stabilizes the inflectional instability similarly to the traditional case. The inertial instability is also strongly affected; for instance, the inertially unstable regime is also extended in the nondiffusive limit as 0 < f < 1 + f̃ 2/N2, where N is the dimensionless Brunt-Väisälä frequency. More strikingly, in the high thermal diffusivity limit, it is always inertially unstable at any colatitude θ except at the poles (i.e., 0° < θ <  180°). We also derived the critical Reynolds numbers for the inertial instability using the asymptotic dispersion relations obtained from the WKBJ analysis. Using the asymptotic and numerical results, we propose a prescription for the effective turbulent viscosities induced by the inertial and inflectional instabilities that can be possibly used in stellar evolution models. The characteristic time of this turbulence is short enough so that it is efficient to redistribute angular momentum and to mix chemicals in stellar radiation zones.","lang":"eng"}],"day":"08","arxiv":1,"doi":"10.1051/0004-6361/202038654","extern":"1","acknowledgement":"The authors acknowledge support from the European Research Council through ERC grant SPIRE 647383 and from GOLF and PLATO CNES grants at the Department of Astrophysics at CEA Paris-Saclay. We thank the referee, Prof. A. J. Barker, for his constructive comments that allow us to improve the article.","volume":646,"author":[{"first_name":"J.","last_name":"Park","full_name":"Park, J."},{"full_name":"Prat, V.","first_name":"V.","last_name":"Prat"},{"full_name":"Mathis, S.","last_name":"Mathis","first_name":"S."},{"first_name":"Lisa Annabelle","last_name":"Bugnet","orcid":"0000-0003-0142-4000","full_name":"Bugnet, Lisa Annabelle","id":"d9edb345-f866-11ec-9b37-d119b5234501"}],"scopus_import":"1","_id":"11609","intvolume":"       646","title":"Horizontal shear instabilities in rotating stellar radiation zones: II. Effects of the full Coriolis acceleration","article_processing_charge":"No","date_created":"2022-07-18T13:24:32Z","publication_status":"published","quality_controlled":"1","article_type":"original","publisher":"EDP Sciences"},{"type":"journal_article","date_published":"2021-11-03T00:00:00Z","publication_identifier":{"issn":["0027-8424"],"eissn":["1091-6490"]},"oa":1,"main_file_link":[{"url":"https://arxiv.org/abs/2103.00023","open_access":"1"}],"user_id":"4359f0d1-fa6c-11eb-b949-802e58b17ae8","status":"public","publication":"Proceedings of the National Academy of Sciences","project":[{"call_identifier":"FWF","_id":"238B8092-32DE-11EA-91FC-C7463DDC885E","name":"Instabilities in pulsating pipe flow of Newtonian and complex fluids","grant_number":"I04188"}],"oa_version":"Preprint","article_number":"e2102350118","month":"11","keyword":["multidisciplinary","elastoinertial turbulence","viscoelastic flows","elastic instability","drag reduction"],"language":[{"iso":"eng"}],"citation":{"mla":"Choueiri, George H., et al. “Experimental Observation of the Origin and Structure of Elastoinertial Turbulence.” <i>Proceedings of the National Academy of Sciences</i>, vol. 118, no. 45, e2102350118, National Academy of Sciences, 2021, doi:<a href=\"https://doi.org/10.1073/pnas.2102350118\">10.1073/pnas.2102350118</a>.","short":"G.H. Choueiri, J.M. Lopez Alonso, A. Varshney, S. Sankar, B. Hof, Proceedings of the National Academy of Sciences 118 (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.","ama":"Choueiri GH, Lopez Alonso JM, Varshney A, Sankar S, Hof B. Experimental observation of the origin and structure of elastoinertial turbulence. <i>Proceedings of the National Academy of Sciences</i>. 2021;118(45). doi:<a href=\"https://doi.org/10.1073/pnas.2102350118\">10.1073/pnas.2102350118</a>","apa":"Choueiri, G. H., Lopez Alonso, J. M., Varshney, A., Sankar, S., &#38; Hof, B. (2021). Experimental observation of the origin and structure of elastoinertial turbulence. <i>Proceedings of the National Academy of Sciences</i>. National Academy of Sciences. <a href=\"https://doi.org/10.1073/pnas.2102350118\">https://doi.org/10.1073/pnas.2102350118</a>","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,” <i>Proceedings of the National Academy of Sciences</i>, vol. 118, no. 45. National Academy of Sciences, 2021.","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.” <i>Proceedings of the National Academy of Sciences</i>. National Academy of Sciences, 2021. <a href=\"https://doi.org/10.1073/pnas.2102350118\">https://doi.org/10.1073/pnas.2102350118</a>."},"year":"2021","date_updated":"2023-08-14T11:50:10Z","external_id":{"arxiv":["2103.00023"],"isi":["000720926900019"],"pmid":[" 34732570"]},"isi":1,"day":"03","doi":"10.1073/pnas.2102350118","arxiv":1,"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."}],"volume":118,"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.","scopus_import":"1","_id":"10299","pmid":1,"issue":"45","author":[{"id":"448BD5BC-F248-11E8-B48F-1D18A9856A87","full_name":"Choueiri, George H","first_name":"George H","last_name":"Choueiri"},{"last_name":"Lopez Alonso","first_name":"Jose M","full_name":"Lopez Alonso, Jose M","orcid":"0000-0002-0384-2022","id":"40770848-F248-11E8-B48F-1D18A9856A87"},{"orcid":"0000-0002-3072-5999","full_name":"Varshney, Atul","first_name":"Atul","last_name":"Varshney","id":"2A2006B2-F248-11E8-B48F-1D18A9856A87"},{"full_name":"Sankar, Sarath","last_name":"Sankar","first_name":"Sarath"},{"orcid":"0000-0003-2057-2754","full_name":"Hof, Björn","first_name":"Björn","last_name":"Hof","id":"3A374330-F248-11E8-B48F-1D18A9856A87"}],"date_created":"2021-11-17T13:24:24Z","department":[{"_id":"BjHo"}],"article_processing_charge":"No","publication_status":"published","intvolume":"       118","title":"Experimental observation of the origin and structure of elastoinertial turbulence","quality_controlled":"1","publisher":"National Academy of Sciences","article_type":"original"},{"date_updated":"2024-02-28T13:14:39Z","year":"2021","citation":{"chicago":"Agrawal, Nishchal. “Transition to Turbulence and Drag Reduction in Particle-Laden Pipe Flows.” Institute of Science and Technology Austria, 2021. <a href=\"https://doi.org/10.15479/at:ista:9728\">https://doi.org/10.15479/at:ista:9728</a>.","ieee":"N. Agrawal, “Transition to turbulence and drag reduction in particle-laden pipe flows,” Institute of Science and Technology Austria, 2021.","ama":"Agrawal N. Transition to turbulence and drag reduction in particle-laden pipe flows. 2021. doi:<a href=\"https://doi.org/10.15479/at:ista:9728\">10.15479/at:ista:9728</a>","apa":"Agrawal, N. (2021). <i>Transition to turbulence and drag reduction in particle-laden pipe flows</i>. Institute of Science and Technology Austria. <a href=\"https://doi.org/10.15479/at:ista:9728\">https://doi.org/10.15479/at:ista:9728</a>","ista":"Agrawal N. 2021. Transition to turbulence and drag reduction in particle-laden pipe flows. Institute of Science and Technology Austria.","short":"N. Agrawal, Transition to Turbulence and Drag Reduction in Particle-Laden Pipe Flows, Institute of Science and Technology Austria, 2021.","mla":"Agrawal, Nishchal. <i>Transition to Turbulence and Drag Reduction in Particle-Laden Pipe Flows</i>. Institute of Science and Technology Austria, 2021, doi:<a href=\"https://doi.org/10.15479/at:ista:9728\">10.15479/at:ista:9728</a>."},"abstract":[{"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.","lang":"eng"}],"doi":"10.15479/at:ista:9728","degree_awarded":"PhD","day":"29","ddc":["532"],"author":[{"id":"469E6004-F248-11E8-B48F-1D18A9856A87","last_name":"Agrawal","first_name":"Nishchal","full_name":"Agrawal, Nishchal"}],"_id":"9728","alternative_title":["ISTA Thesis"],"title":"Transition to turbulence and drag reduction in particle-laden pipe flows","publication_status":"published","department":[{"_id":"GradSch"},{"_id":"BjHo"}],"date_created":"2021-07-27T13:40:30Z","article_processing_charge":"No","file_date_updated":"2022-07-29T22:30:05Z","page":"118","publisher":"Institute of Science and Technology Austria","date_published":"2021-07-29T00:00:00Z","type":"dissertation","tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","short":"CC BY (4.0)","image":"/images/cc_by.png","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)"},"supervisor":[{"id":"3A374330-F248-11E8-B48F-1D18A9856A87","orcid":"0000-0003-2057-2754","full_name":"Hof, Björn","first_name":"Björn","last_name":"Hof"}],"oa":1,"publication_identifier":{"issn":["2663-337X"]},"related_material":{"record":[{"status":"public","relation":"part_of_dissertation","id":"6189"}]},"status":"public","user_id":"c635000d-4b10-11ee-a964-aac5a93f6ac1","file":[{"file_id":"9744","creator":"nagrawal","relation":"source_file","access_level":"closed","date_updated":"2022-07-29T22:30:05Z","file_name":"Transition to Turbulence and Drag Reduction in Particle-Laden Pipe Flows.zip","content_type":"application/x-zip-compressed","date_created":"2021-07-28T13:32:02Z","embargo_to":"open_access","checksum":"77436be3563a90435024307b1b5ee7e8","file_size":22859658},{"date_updated":"2022-07-29T22:30:05Z","file_name":"Transition to Turbulence and Drag Reduction in Particle-Laden Pipe Flows.pdf","content_type":"application/pdf","date_created":"2021-07-28T13:32:05Z","embargo":"2022-07-28","file_size":18658048,"checksum":"72a891d7daba85445c29b868c22575ed","file_id":"9745","creator":"nagrawal","relation":"main_file","access_level":"open_access"}],"has_accepted_license":"1","month":"07","oa_version":"Published Version","acknowledged_ssus":[{"_id":"M-Shop"}],"language":[{"iso":"eng"}],"keyword":["Drag Reduction","Transition to Turbulence","Multiphase Flows","particle Laden Flows","Complex Flows","Experiments","Fluid Dynamics"]},{"language":[{"iso":"eng"}],"keyword":["Instabilities","Turbulence","Nonlinear dynamics"],"has_accepted_license":"1","oa_version":"Published Version","month":"10","file":[{"access_level":"closed","relation":"source_file","creator":"cparanjape","file_id":"6962","file_size":45828099,"checksum":"7ba298ba0ce7e1d11691af6b8eaf0a0a","date_created":"2019-10-23T09:54:43Z","content_type":"application/zip","file_name":"Chaitanya_Paranjape_source_files_tex_figures.zip","date_updated":"2020-07-14T12:47:46Z"},{"file_id":"6963","creator":"cparanjape","relation":"main_file","access_level":"open_access","date_updated":"2020-07-14T12:47:46Z","content_type":"application/pdf","file_name":"Chaitanya_Paranjape_Thesis.pdf","date_created":"2019-10-23T10:37:09Z","file_size":19504197,"checksum":"642697618314e31ac31392da7909c2d9"}],"user_id":"c635000d-4b10-11ee-a964-aac5a93f6ac1","status":"public","date_published":"2019-10-24T00:00:00Z","type":"dissertation","publication_identifier":{"eissn":["2663-337X"]},"supervisor":[{"id":"3A374330-F248-11E8-B48F-1D18A9856A87","last_name":"Hof","first_name":"Björn","full_name":"Hof, Björn","orcid":"0000-0003-2057-2754"}],"oa":1,"page":"138","file_date_updated":"2020-07-14T12:47:46Z","publisher":"Institute of Science and Technology Austria","_id":"6957","author":[{"id":"3D85B7C4-F248-11E8-B48F-1D18A9856A87","first_name":"Chaitanya S","last_name":"Paranjape","full_name":"Paranjape, Chaitanya S"}],"publication_status":"published","article_processing_charge":"No","department":[{"_id":"BjHo"}],"date_created":"2019-10-22T12:08:43Z","title":"Onset of turbulence in plane Poiseuille flow","alternative_title":["ISTA Thesis"],"ddc":["532"],"date_updated":"2023-09-07T12:53:25Z","year":"2019","citation":{"ieee":"C. S. Paranjape, “Onset of turbulence in plane Poiseuille flow,” Institute of Science and Technology Austria, 2019.","chicago":"Paranjape, Chaitanya S. “Onset of Turbulence in Plane Poiseuille Flow.” Institute of Science and Technology Austria, 2019. <a href=\"https://doi.org/10.15479/AT:ISTA:6957\">https://doi.org/10.15479/AT:ISTA:6957</a>.","apa":"Paranjape, C. S. (2019). <i>Onset of turbulence in plane Poiseuille flow</i>. Institute of Science and Technology Austria. <a href=\"https://doi.org/10.15479/AT:ISTA:6957\">https://doi.org/10.15479/AT:ISTA:6957</a>","ama":"Paranjape CS. Onset of turbulence in plane Poiseuille flow. 2019. doi:<a href=\"https://doi.org/10.15479/AT:ISTA:6957\">10.15479/AT:ISTA:6957</a>","ista":"Paranjape CS. 2019. Onset of turbulence in plane Poiseuille flow. Institute of Science and Technology Austria.","mla":"Paranjape, Chaitanya S. <i>Onset of Turbulence in Plane Poiseuille Flow</i>. Institute of Science and Technology Austria, 2019, doi:<a href=\"https://doi.org/10.15479/AT:ISTA:6957\">10.15479/AT:ISTA:6957</a>.","short":"C.S. Paranjape, Onset of Turbulence in Plane Poiseuille Flow, Institute of Science and Technology Austria, 2019."},"degree_awarded":"PhD","doi":"10.15479/AT:ISTA:6957","day":"24","abstract":[{"text":"In many shear flows like pipe flow, plane Couette flow, plane Poiseuille flow,  etc. turbulence emerges subcritically. Here, when subjected to strong enough perturbations, the flow becomes turbulent in spite of the laminar base flow being linearly stable.  The nature of this instability has puzzled the scientific community for decades. At onset, turbulence appears in localized patches and flows are spatio-temporally intermittent.  In pipe flow the localized turbulent structures are referred to as puffs and in planar flows like plane Couette and channel flow, patches arise in the form of localized oblique bands. In this thesis, we study the onset of turbulence in channel flow in direct numerical simulations from a dynamical system theory perspective, as well as by performing experiments in a large aspect ratio channel.\r\n\r\nThe aim of the experimental work is to determine the critical Reynolds number where turbulence first becomes sustained. Recently, the onset of turbulence has been described in analogy to absorbing state phase transition (i.e. directed percolation). In particular, it has been shown that the critical point can be estimated from the competition between spreading and decay processes. Here, by performing experiments, we identify the mechanisms underlying turbulence proliferation in channel flow and find the critical Reynolds number, above which turbulence becomes sustained. Above the critical point, the continuous growth at the tip of the stripes outweighs the stochastic shedding of turbulent patches at the tail and the stripes expand. For growing stripes, the probability to decay decreases while the probability of stripe splitting increases. Consequently, and unlike for the puffs in pipe flow, neither of these two processes is time-independent i.e. memoryless. Coupling between stripe expansion and creation of new stripes via splitting leads to a significantly lower critical point ($Re_c=670+/-10$) than most earlier studies suggest.  \r\n\r\nWhile the above approach sheds light on how turbulence first becomes sustained, it provides no insight into the origin of the stripes themselves. In the numerical part of the thesis we investigate how turbulent stripes form from invariant solutions of the Navier-Stokes equations. The origin of these turbulent stripes can be identified by applying concepts from the dynamical system theory. In doing so, we identify the exact coherent structures underlying stripes and their bifurcations and how they give rise to the turbulent attractor in phase space. We first report a family of localized nonlinear traveling wave solutions of the Navier-Stokes equations in channel flow. These solutions show structural similarities with turbulent stripes in experiments like obliqueness, quasi-streamwise streaks and vortices, etc. A parametric study of these traveling wave solution is performed, with parameters like Reynolds number, stripe tilt angle and domain size, including the stability of the solutions. These solutions emerge through saddle-node bifurcations and form a phase space skeleton for the turbulent stripes observed in the experiments. The lower branches of these TW solutions at different tilt angles undergo Hopf bifurcation and new solutions branches of relative periodic orbits emerge. These RPO solutions do not belong to the same family and therefore the routes to chaos for different angles are different.  \r\n\r\nIn shear flows, turbulence at onset is transient in nature.  Consequently,turbulence can not be tracked to lower Reynolds numbers, where the dynamics may simplify. Before this happens, turbulence becomes short-lived and laminarizes. In the last part of the thesis, we show that using numerical simulations we can continue turbulent stripes in channel flow past the 'relaminarization barrier' all the way to their origin. Here, turbulent stripe dynamics simplifies and the fluctuations are no longer stochastic and the stripe settles down to a relative periodic orbit. This relative periodic orbit originates from the aforementioned traveling wave solutions. Starting from the relative periodic orbit, a small increase in speed i.e. Reynolds number gives rise to chaos and the attractor dimension sharply increases in contrast to the classical transition scenario where the instabilities affect the flow globally and give rise to much more gradual route to turbulence.","lang":"eng"}]}]