Stability of quasi-Keplerian Shear Flow in a Laboratory Experiment

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Subcritical transition to turbulence has been proposed as a source of turbulent viscosity required for the associated angular momentum transport for fast accretion in Keplerian disks. Previously cited laboratory experiments in supporting this hypothesis were performed either in a di erent type of flow than Keplerian or without quantitative measurements of angular momentum transport and mean flow profile, and all of them appear to su er from Ekman e ects, secondary flows induced by nonoptimal axial boundary conditions. Such Ekman e ects are expected to be absent from astronomical disks, which probably have stress-free vertical boundaries unless strongly magnetized. Aims. ... continued below

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Schartman, Ethan; Ji, Hantao; Burin, Michael J. & Goodman, Jeremy June 19, 2012.

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Subcritical transition to turbulence has been proposed as a source of turbulent viscosity required for the associated angular momentum transport for fast accretion in Keplerian disks. Previously cited laboratory experiments in supporting this hypothesis were performed either in a di erent type of flow than Keplerian or without quantitative measurements of angular momentum transport and mean flow profile, and all of them appear to su er from Ekman e ects, secondary flows induced by nonoptimal axial boundary conditions. Such Ekman e ects are expected to be absent from astronomical disks, which probably have stress-free vertical boundaries unless strongly magnetized. Aims. To quantify angular momentum transport due to subcritical hydrodynamic turbulence, if exists, in a quasi-Keplerian flow with minimized Ekman e ects. Methods.We perform a local measurement of the azimuthal-radial component of the Reynolds stress tensor in a novel laboratory apparatus where Ekman e ects are minimized by flexible control of axial boundary conditions. Results.We find significant Ekman e ects on angular momentum transport due to nonoptimal axial boundary conditions in quasi-Keplerian flows. With the optimal control of Ekman e ects, no statistically meaningful angular momentum transport is detected in such flows at Reynolds number up to two millions. Conclusions. Either a subcritical transition does not occur, or, if a subcritical transition does occur, the associated radial transport of angular momentum in optimized quasi-Keplerian laboratory flows is too small to directly support the hypothesis that subcritical hydrodynamic turbulence is responsible for accretion in astrophysical disks. Possible limitations in applying laboratory results to astrophysical disks due to experimental geometry are discussed.

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  • Astronomy and Astrophysics (Decemer 2010)

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  • Report No.: PPPL-4771
  • Grant Number: DE-ACO2-09CH11466
  • Office of Scientific & Technical Information Report Number: 1059260
  • Archival Resource Key: ark:/67531/metadc832154

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  • June 19, 2012

Added to The UNT Digital Library

  • May 19, 2016, 9:45 a.m.

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  • July 18, 2016, 5:28 p.m.

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Schartman, Ethan; Ji, Hantao; Burin, Michael J. & Goodman, Jeremy. Stability of quasi-Keplerian Shear Flow in a Laboratory Experiment, report, June 19, 2012; Princeton, New Jersey. (digital.library.unt.edu/ark:/67531/metadc832154/: accessed June 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.