Ekman boundary layers in a fluid filled precessing cylinder

Pizzi, Federico; Giesecke, A.; Stefani, Frank

doi:10.1063/5.0037922

Cited by 10 publications

(1 citation statement)

References 50 publications

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“…In the phase diagram Fig. 4 that lies in the rich and optimal flow structure for this nutation angle 28,32 . With view on Fig.…”

Section: Conclusion and Prospectsmentioning

confidence: 94%

The effect of nutation angle on the flow inside a precessing cylinder and its dynamo action

Kumar¹,

Pizzi²,

Giesecke³

et al. 2022

Preprint

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The effect of the nutation angle on the flow inside a precessing cylinder is experimentally explored and compared with numerical simulations. The focus is laid on the typical breakdown of the directly forced m = 1 Kelvin mode for increasing precession ratio (Poincaré number), and the accompanying transition between a laminar and turbulent flow. Compared to the reference case with a 90 • nutation angle, prograde rotation leads to an earlier breakdown, while in the retrograde case the forced mode continues to exist also for higher Poincaré numbers. Depending largely on the occurrence and intensity of an axisymmetric double-roll mode, a kinematic dynamo study reveals a sensitive dependency of the self-excitation condition on the nutation angle and the Poincaré number. Optimal dynamo conditions are found for 90 • angle which, however, might shift to slightly retrograde precession for higher Reynolds numbers.

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“…In the phase diagram Fig. 4 that lies in the rich and optimal flow structure for this nutation angle 28,32 . With view on Fig.…”

Section: Conclusion and Prospectsmentioning

confidence: 94%

The effect of nutation angle on the flow inside a precessing cylinder and its dynamo action

Kumar¹,

Pizzi²,

Giesecke³

et al. 2022

Preprint

Self Cite

View full text Add to dashboard Cite

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The global flow state in a precessing cylinder

Giesecke,

Vogt,

Pizzi

et al. 2024

J. Fluid Mech.

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We examine the fluid flow forced by precession of a rotating cylindrical container using numerical simulations and experimental flow measurements with ultrasonic Doppler velocimetry. The analysis is based on the decomposition of the flow field into contributions with distinct azimuthal symmetry or analytically known inertial modes and the corresponding calculation of their amplitudes. We show that the predominant fraction of the kinetic energy of the precession-driven fluid flow is contained only within a few large-scale modes. The most striking observation shown by simulations and experiments is the transition from a flow dominated by large-scale structures to a more turbulent behaviour with the small-scale fluctuations becoming increasingly important. At a fixed rotation frequency (parametrized by the Reynolds number, $Re$ ) this transition occurs when a critical precession ratio is exceeded and consists of a two-stage collapse of the directly driven flow going along with a massive modification of the azimuthal circulation (the zonal flow) and the appearance of an axisymmetric double-roll mode limited to a narrow range of precession ratios. A similar behaviour is found in experiments which make it possible to follow the transition up to Reynolds numbers of $Re\approx 2\times 10^6$ . We find that the critical precession ratio decreases with rotation, initially showing a particular scaling ${\propto }Re^{-({1}/{5})}$ but developing an asymptotic behaviour for $Re\gtrsim 10^5$ which might be explained by the onset of turbulence in boundary layers.

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Precessing non-axisymmetric ellipsoids: bi-stability and fluid instabilities

Burmann,

Kira,

Noir

2024

J. Fluid Mech.

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This study explores precession-driven flows in a non-axisymmetric ellipsoid spinning around its medium axis. Using an experimental approach, we focus on two aspects of the flow: the base flow of uniform vorticity and the development of fluid instabilities. In contrast to a preceding paper (J. Fluid. Mech., vol. 932, 2022, A24), where the ellipsoid rotated around its shortest axis, we do not observe bi-stability or hysteresis of the base flow, but a continuous transition from small to large differential rotation and tilt of the fluid rotation axis. We then use the model developed by Noir & Cébron (J. Fluid. Mech., vol. 737, 2013, pp. 412–439) to numerically determine regions in the parameter space of axial and equatorial deformations for which bi-stability may exist. Concerning fluid instabilities, we use three independent observations to track the onset of both boundary layer and parametric instabilities. Our results clearly show the presence of a parametric instability, yet the exact nature of the underlying mechanism (conical shear layer instability, shear instability and elliptical instability) is not unambiguously identified. A coexisting boundary layer instability, although unlikely, cannot be ruled out based on our experimental data. To make further progress on this topic, a new generation of experiments at significantly lower Ekman numbers (ratio of rotation and viscous time scales) is clearly needed.

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Ekman boundary layers in a fluid filled precessing cylinder

Cited by 10 publications

References 50 publications

The effect of nutation angle on the flow inside a precessing cylinder and its dynamo action

The effect of nutation angle on the flow inside a precessing cylinder and its dynamo action

The global flow state in a precessing cylinder

Precessing non-axisymmetric ellipsoids: bi-stability and fluid instabilities

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