--- _id: '1837' abstract: - lang: eng text: 'Transition to turbulence in straight pipes occurs in spite of the linear stability of the laminar Hagen-Poiseuille flow if both the amplitude of flow perturbations and the Reynolds number Re exceed a minimum threshold (subcritical transition). As the pipe curvature increases, centrifugal effects become important, modifying the basic flow as well as the most unstable linear modes. If the curvature (tube-to-coiling diameter d/D) is sufficiently large, a Hopf bifurcation (supercritical instability) is encountered before turbulence can be excited (subcritical instability). We trace the instability thresholds in the Re - d/D parameter space in the range 0.01 ≤ d/D\ ≤ 0.1 by means of laser-Doppler velocimetry and determine the point where the subcritical and supercritical instabilities meet. Two different experimental set-ups are used: a closed system where the pipe forms an axisymmetric torus and an open system employing a helical pipe. Implications for the measurement of friction factors in curved pipes are discussed.' article_number: R3 article_processing_charge: No article_type: original author: - first_name: Jakob full_name: Kühnen, Jakob id: 3A47AE32-F248-11E8-B48F-1D18A9856A87 last_name: Kühnen orcid: 0000-0003-4312-0179 - first_name: P full_name: Braunshier, P last_name: Braunshier - first_name: M full_name: Schwegel, M last_name: Schwegel - first_name: Hendrik full_name: Kuhlmann, Hendrik last_name: Kuhlmann - first_name: Björn full_name: Hof, Björn id: 3A374330-F248-11E8-B48F-1D18A9856A87 last_name: Hof orcid: 0000-0003-2057-2754 citation: ama: Kühnen J, Braunshier P, Schwegel M, Kuhlmann H, Hof B. Subcritical versus supercritical transition to turbulence in curved pipes. Journal of Fluid Mechanics. 2015;770(5). doi:10.1017/jfm.2015.184 apa: Kühnen, J., Braunshier, P., Schwegel, M., Kuhlmann, H., & Hof, B. (2015). Subcritical versus supercritical transition to turbulence in curved pipes. Journal of Fluid Mechanics. Cambridge University Press. https://doi.org/10.1017/jfm.2015.184 chicago: Kühnen, Jakob, P Braunshier, M Schwegel, Hendrik Kuhlmann, and Björn Hof. “Subcritical versus Supercritical Transition to Turbulence in Curved Pipes.” Journal of Fluid Mechanics. Cambridge University Press, 2015. https://doi.org/10.1017/jfm.2015.184. ieee: J. Kühnen, P. Braunshier, M. Schwegel, H. Kuhlmann, and B. Hof, “Subcritical versus supercritical transition to turbulence in curved pipes,” Journal of Fluid Mechanics, vol. 770, no. 5. Cambridge University Press, 2015. ista: Kühnen J, Braunshier P, Schwegel M, Kuhlmann H, Hof B. 2015. Subcritical versus supercritical transition to turbulence in curved pipes. Journal of Fluid Mechanics. 770(5), R3. mla: Kühnen, Jakob, et al. “Subcritical versus Supercritical Transition to Turbulence in Curved Pipes.” Journal of Fluid Mechanics, vol. 770, no. 5, R3, Cambridge University Press, 2015, doi:10.1017/jfm.2015.184. short: J. Kühnen, P. Braunshier, M. Schwegel, H. Kuhlmann, B. Hof, Journal of Fluid Mechanics 770 (2015). date_created: 2018-12-11T11:54:17Z date_published: 2015-04-08T00:00:00Z date_updated: 2021-01-12T06:53:31Z day: '08' department: - _id: BjHo doi: 10.1017/jfm.2015.184 ec_funded: 1 external_id: arxiv: - '1508.06559' intvolume: ' 770' issue: '5' language: - iso: eng main_file_link: - open_access: '1' url: https://arxiv.org/abs/1508.06559 month: '04' oa: 1 oa_version: Preprint project: - _id: 25152F3A-B435-11E9-9278-68D0E5697425 call_identifier: FP7 grant_number: '306589' name: Decoding the complexity of turbulence at its origin publication: Journal of Fluid Mechanics publication_status: published publisher: Cambridge University Press publist_id: '5265' quality_controlled: '1' scopus_import: 1 status: public title: Subcritical versus supercritical transition to turbulence in curved pipes type: journal_article user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87 volume: 770 year: '2015' ...