Experimental investigation of unsteady separation in the rotor-oscillator flow

Visualisations of various types of flow separation are presented in an experimental set-up that translates a rotating cylinder parallel to a wall. Particle image velocimetry is used to measure the two velocity components in a plane perpendicular to the cylinder where the flow is two-dimensional. To spatially resolve the flow close to the wall, a high-viscosity fluid is used. For a periodic translation, the fixed separation is compared to the theory of Haller (J. Fluid Mech., vol. 512, 2004, pp. 257–311), while for non-periodic translations, a method is proposed to extract the moving separation point captured by a Lagrangian saddle point, and its finite-time unstable direction (separation profiles). Intermediate cases are also presented where both types of separation, fixed and moving, are either present simultaneously or appear successively. Some results issued from numerical simulations of an impinging jet show that all the cases observed in the rotor-oscillator flow are not restricted to high-viscosity fluid motions but may also occur within any vortical flow.

JFM classification

Boundary Layers: Boundary Layers Boundary Layers: Boundary layer separation Low-Reynolds-number flows: Low-Reynolds-number flows

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JFM Papers

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Journal of Fluid Mechanics , Volume 844 , 10 June 2018 , pp. 546 - 566

DOI: https://doi.org/10.1017/jfm.2018.188

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Lamarche-Gagnon et al, supplementary movie 1

Visualisation of separation for the periodic flow with H = 2D

Video 4 MB

Lamarche-Gagnon et al, supplementary movie 2

Visualisation of separation for the periodic flow with H = D

Video 1 MB

Lamarche-Gagnon et al, supplementary movie 3

Prediction of moving separation

Video 345 KB

Lamarche-Gagnon et al, supplementary movie 4

Ejection of particles for the case of the periodic flow with a long period

Video 12 MB

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Experimental investigation of unsteady separation in the rotor-oscillator flow

Volume 844
Marc-Étienne Lamarche-Gagnon ^(a1) and Jérôme Vétel ^(a1)
DOI: https://doi.org/10.1017/jfm.2018.188

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Article contents

Experimental investigation of unsteady separation in the rotor-oscillator flow

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References

Lamarche-Gagnon et al, supplementary movie 1

Lamarche-Gagnon et al, supplementary movie 2

Lamarche-Gagnon et al, supplementary movie 3

Lamarche-Gagnon et al, supplementary movie 4

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