[{"main_file_link":[{"url":"https://arxiv.org/abs/2005.11190","open_access":"1"}],"scopus_import":"1","intvolume":" 117","month":"05","abstract":[{"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.","lang":"eng"}],"oa_version":"Preprint","ec_funded":1,"issue":"21","volume":117,"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":[{"relation":"dissertation_contains","id":"12726","status":"public"},{"id":"14530","status":"public","relation":"dissertation_contains"}]},"publication_status":"published","publication_identifier":{"issn":["00278424"],"eissn":["10916490"]},"language":[{"iso":"eng"}],"type":"journal_article","article_type":"original","status":"public","_id":"7932","department":[{"_id":"BjHo"}],"date_updated":"2023-11-30T10:55:13Z","oa":1,"quality_controlled":"1","publisher":"National Academy of Sciences","page":"11233-11239","date_created":"2020-06-07T22:00:51Z","doi":"10.1073/pnas.1913716117","date_published":"2020-05-26T00:00:00Z","year":"2020","isi":1,"publication":"Proceedings of the National Academy of Sciences of the United States of America","day":"26","project":[{"_id":"238B8092-32DE-11EA-91FC-C7463DDC885E","call_identifier":"FWF","name":"Instabilities in pulsating pipe flow of Newtonian and complex fluids","grant_number":"I04188"},{"call_identifier":"H2020","_id":"260C2330-B435-11E9-9278-68D0E5697425","grant_number":"754411","name":"ISTplus - Postdoctoral Fellowships"}],"external_id":{"isi":["000536797100014"],"arxiv":["2005.11190"]},"article_processing_charge":"No","author":[{"first_name":"Duo","id":"3454D55E-F248-11E8-B48F-1D18A9856A87","last_name":"Xu","full_name":"Xu, Duo"},{"first_name":"Atul","id":"2A2006B2-F248-11E8-B48F-1D18A9856A87","last_name":"Varshney","full_name":"Varshney, Atul","orcid":"0000-0002-3072-5999"},{"last_name":"Ma","full_name":"Ma, Xingyu","orcid":"0000-0002-0179-9737","first_name":"Xingyu","id":"34BADBA6-F248-11E8-B48F-1D18A9856A87"},{"first_name":"Baofang","full_name":"Song, Baofang","last_name":"Song"},{"id":"3BE60946-F248-11E8-B48F-1D18A9856A87","first_name":"Michael","last_name":"Riedl","orcid":"0000-0003-4844-6311","full_name":"Riedl, Michael"},{"first_name":"Marc","full_name":"Avila, Marc","last_name":"Avila"},{"id":"3A374330-F248-11E8-B48F-1D18A9856A87","first_name":"Björn","last_name":"Hof","orcid":"0000-0003-2057-2754","full_name":"Hof, Björn"}],"title":"Nonlinear hydrodynamic instability and turbulence in pulsatile flow","citation":{"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.","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.","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.","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","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","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."},"user_id":"4359f0d1-fa6c-11eb-b949-802e58b17ae8"},{"publisher":"Cambridge University Press","quality_controlled":"1","oa":1,"page":"418 - 432","date_published":"2017-11-25T00:00:00Z","doi":"10.1017/jfm.2017.620","date_created":"2018-12-11T11:48:17Z","isi":1,"year":"2017","day":"25","publication":"Journal of Fluid Mechanics","project":[{"_id":"25152F3A-B435-11E9-9278-68D0E5697425","call_identifier":"FP7","grant_number":"306589","name":"Decoding the complexity of turbulence at its origin"}],"author":[{"last_name":"Xu","full_name":"Xu, Duo","id":"3454D55E-F248-11E8-B48F-1D18A9856A87","first_name":"Duo"},{"full_name":"Warnecke, Sascha","last_name":"Warnecke","first_name":"Sascha"},{"full_name":"Song, Baofang","last_name":"Song","first_name":"Baofang"},{"last_name":"Ma","orcid":"0000-0002-0179-9737","full_name":"Ma, Xingyu","first_name":"Xingyu","id":"34BADBA6-F248-11E8-B48F-1D18A9856A87"},{"orcid":"0000-0003-2057-2754","full_name":"Hof, Björn","last_name":"Hof","first_name":"Björn","id":"3A374330-F248-11E8-B48F-1D18A9856A87"}],"publist_id":"6922","article_processing_charge":"No","external_id":{"isi":["000412934800005"]},"title":"Transition to turbulence in pulsating pipe flow","citation":{"mla":"Xu, Duo, et al. “Transition to Turbulence in Pulsating Pipe Flow.” Journal of Fluid Mechanics, vol. 831, Cambridge University Press, 2017, pp. 418–32, doi:10.1017/jfm.2017.620.","ama":"Xu D, Warnecke S, Song B, Ma X, Hof B. Transition to turbulence in pulsating pipe flow. Journal of Fluid Mechanics. 2017;831:418-432. doi:10.1017/jfm.2017.620","apa":"Xu, D., Warnecke, S., Song, B., Ma, X., & Hof, B. (2017). Transition to turbulence in pulsating pipe flow. Journal of Fluid Mechanics. Cambridge University Press. https://doi.org/10.1017/jfm.2017.620","ieee":"D. Xu, S. Warnecke, B. Song, X. Ma, and B. Hof, “Transition to turbulence in pulsating pipe flow,” Journal of Fluid Mechanics, vol. 831. Cambridge University Press, pp. 418–432, 2017.","short":"D. Xu, S. Warnecke, B. Song, X. Ma, B. Hof, Journal of Fluid Mechanics 831 (2017) 418–432.","chicago":"Xu, Duo, Sascha Warnecke, Baofang Song, Xingyu Ma, and Björn Hof. “Transition to Turbulence in Pulsating Pipe Flow.” Journal of Fluid Mechanics. Cambridge University Press, 2017. https://doi.org/10.1017/jfm.2017.620.","ista":"Xu D, Warnecke S, Song B, Ma X, Hof B. 2017. Transition to turbulence in pulsating pipe flow. Journal of Fluid Mechanics. 831, 418–432."},"user_id":"c635000d-4b10-11ee-a964-aac5a93f6ac1","scopus_import":"1","main_file_link":[{"url":"https://arxiv.org/abs/1709.03738","open_access":"1"}],"month":"11","intvolume":" 831","abstract":[{"text":"Fluid flows in nature and applications are frequently subject to periodic velocity modulations. Surprisingly, even for the generic case of flow through a straight pipe, there is little consensus regarding the influence of pulsation on the transition threshold to turbulence: while most studies predict a monotonically increasing threshold with pulsation frequency (i.e. Womersley number, ), others observe a decreasing threshold for identical parameters and only observe an increasing threshold at low . In the present study we apply recent advances in the understanding of transition in steady shear flows to pulsating pipe flow. For moderate pulsation amplitudes we find that the first instability encountered is subcritical (i.e. requiring finite amplitude disturbances) and gives rise to localized patches of turbulence ('puffs') analogous to steady pipe flow. By monitoring the impact of pulsation on the lifetime of turbulence we map the onset of turbulence in parameter space. Transition in pulsatile flow can be separated into three regimes. At small Womersley numbers the dynamics is dominated by the decay turbulence suffers during the slower part of the cycle and hence transition is delayed significantly. As shown in this regime thresholds closely agree with estimates based on a quasi-steady flow assumption only taking puff decay rates into account. The transition point predicted in the zero limit equals to the critical point for steady pipe flow offset by the oscillation Reynolds number (i.e. the dimensionless oscillation amplitude). In the high frequency limit on the other hand, puff lifetimes are identical to those in steady pipe flow and hence the transition threshold appears to be unaffected by flow pulsation. In the intermediate frequency regime the transition threshold sharply drops (with increasing ) from the decay dominated (quasi-steady) threshold to the steady pipe flow level.","lang":"eng"}],"oa_version":"Submitted Version","volume":831,"ec_funded":1,"publication_identifier":{"issn":["00221120"]},"publication_status":"published","language":[{"iso":"eng"}],"type":"journal_article","status":"public","_id":"745","department":[{"_id":"BjHo"}],"date_updated":"2023-09-27T12:28:12Z"},{"publist_id":"5928","author":[{"first_name":"Gerard","last_name":"Verbiest","full_name":"Verbiest, Gerard"},{"last_name":"Xu","full_name":"Xu, Duo","id":"3454D55E-F248-11E8-B48F-1D18A9856A87","first_name":"Duo"},{"last_name":"Goldsche","full_name":"Goldsche, Matthias","first_name":"Matthias"},{"full_name":"Khodkov, Timofiy","last_name":"Khodkov","first_name":"Timofiy"},{"first_name":"Shabir","id":"2D25E1F6-F248-11E8-B48F-1D18A9856A87","last_name":"Barzanjeh","full_name":"Barzanjeh, Shabir","orcid":"0000-0003-0415-1423"},{"first_name":"Nils","last_name":"Von Den Driesch","full_name":"Von Den Driesch, Nils"},{"first_name":"Dan","last_name":"Buca","full_name":"Buca, Dan"},{"full_name":"Stampfer, Christoph","last_name":"Stampfer","first_name":"Christoph"}],"department":[{"_id":"JoFi"}],"title":"Tunable mechanical coupling between driven microelectromechanical resonators","date_updated":"2023-02-21T10:35:06Z","citation":{"ista":"Verbiest G, Xu D, Goldsche M, Khodkov T, Barzanjeh S, Von Den Driesch N, Buca D, Stampfer C. 2016. Tunable mechanical coupling between driven microelectromechanical resonators. Applied Physics Letter. 109, 143507.","chicago":"Verbiest, Gerard, Duo Xu, Matthias Goldsche, Timofiy Khodkov, Shabir Barzanjeh, Nils Von Den Driesch, Dan Buca, and Christoph Stampfer. “Tunable Mechanical Coupling between Driven Microelectromechanical Resonators.” Applied Physics Letter. American Institute of Physics, 2016. https://doi.org/10.1063/1.4964122.","apa":"Verbiest, G., Xu, D., Goldsche, M., Khodkov, T., Barzanjeh, S., Von Den Driesch, N., … Stampfer, C. (2016). Tunable mechanical coupling between driven microelectromechanical resonators. Applied Physics Letter. American Institute of Physics. https://doi.org/10.1063/1.4964122","ama":"Verbiest G, Xu D, Goldsche M, et al. Tunable mechanical coupling between driven microelectromechanical resonators. Applied Physics Letter. 2016;109. doi:10.1063/1.4964122","short":"G. Verbiest, D. Xu, M. Goldsche, T. Khodkov, S. Barzanjeh, N. Von Den Driesch, D. Buca, C. Stampfer, Applied Physics Letter 109 (2016).","ieee":"G. Verbiest et al., “Tunable mechanical coupling between driven microelectromechanical resonators,” Applied Physics Letter, vol. 109. American Institute of Physics, 2016.","mla":"Verbiest, Gerard, et al. “Tunable Mechanical Coupling between Driven Microelectromechanical Resonators.” Applied Physics Letter, vol. 109, 143507, American Institute of Physics, 2016, doi:10.1063/1.4964122."},"user_id":"3E5EF7F0-F248-11E8-B48F-1D18A9856A87","type":"journal_article","status":"public","_id":"1339","article_number":"143507","date_created":"2018-12-11T11:51:28Z","date_published":"2016-10-04T00:00:00Z","doi":"10.1063/1.4964122","volume":109,"publication_status":"published","year":"2016","language":[{"iso":"eng"}],"publication":"Applied Physics Letter","day":"04","main_file_link":[{"url":"https://arxiv.org/abs/1607.04406","open_access":"1"}],"oa":1,"publisher":"American Institute of Physics","quality_controlled":"1","scopus_import":1,"intvolume":" 109","month":"10","abstract":[{"lang":"eng","text":"We present a microelectromechanical system, in which a silicon beam is attached to a comb-drive\r\nactuator, which is used to tune the tension in the silicon beam and thus its resonance frequency. By\r\nmeasuring the resonance frequencies of the system, we show that the comb-drive actuator and the\r\nsilicon beam behave as two strongly coupled resonators. Interestingly, the effective coupling rate\r\n(1.5 MHz) is tunable with the comb-drive actuator (10%) as well as with a side-gate (10%)\r\nplaced close to the silicon beam. In contrast, the effective spring constant of the system is insensitive\r\nto either of them and changes only by 60.5%. Finally, we show that the comb-drive actuator\r\ncan be used to switch between different coupling rates with a frequency of at least 10 kHz.\r\n"}],"acknowledgement":"We acknowledge the support from the Helmholtz Nanoelectronic Facility (HNF) and funding from the ERC (GA-Nr. 280140).","oa_version":"Preprint"}]