Torque reduction in Taylor–Couette flows subject to an axial pressure gradient

Manna, M.; Vacca, Andrea

doi:10.1017/s0022112009991078

Cited by 13 publications

(24 citation statements)

References 43 publications

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“…What has not yet been considered is the effect of the axial pressure gradient, which has been shown in some cases to reduce the torque requirement (Manna and Vacca, 2009), although the Taylor numbers in the present study are much higher than covered by Manna and Vacca thus the observed torque reduction is unlikely to manifest here. A formula for the effect of axial pressure gradient on friction torque was developed by Yamada (1962) although it is based on the axial Reynolds number which is not known in the present work and consequently cannot be used to improve the torque estimation.…”

Section: Steady State Simulation Methodsmentioning

confidence: 51%

Numerical modelling of rotor–stator interaction in rim driven thrusters

2015

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An electric rim driven thruster is a relatively new marine propulsion device and the associated fluid dynamics have not been fully investigated. This work develops a robust CFD method and investigates both frozen rotor and unsteady simulations of rotor-stator interaction.Two solvers from OpenFOAM were used. Steady state simulations were performed using MRFSimpleFoam with a frozen rotor treatment of the interface between static and rotational reference frames. The solver for unsteady simulations was pimpleDyMFoam, utilising a sliding mesh interface to handle the dynamic meshing. Both methods are thoroughly verified and validated against experimental data. The k-omega SST turbulence model is found to be robust down to low advance ratios.For the rim driven thruster, analytical models are used to estimate friction forces in the rim gap and their contribution to torque losses. The frozen rotor and unsteady treatments of rotor-stator interaction are compared and found to have similar trends in the variation of thrust produced. However, the frozen rotor method does not predict the same variation of instantaneous torque and does not capture the rotor-stator interaction fully. Analysis of the unsteady rotor-stator interaction shows an oscillating flow over the stators and thus inflow to the blades. Keywords:Frozen Rotor, Unsteady, Numerical, CFD, Thruster, Rim Driven

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Section: Steady State Simulation Methodsmentioning

confidence: 51%

Numerical modelling of rotor–stator interaction in rim driven thrusters

2015

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“…This reduction in plume ejection results in a reduced transport of angular velocity (torque). A similar reduction in the torque caused by a mean flow was also seen when forcing the flow with an axial pressure gradient by Manna & Vacca (2009). Vortices with a smaller wavelength have smaller wind-sheared regions and thus result in a larger N u ω , if this suppression is taking place.…”

Section: Dependence On Number and Size Of Rollsmentioning

confidence: 56%

Exploring the phase diagram of fully turbulent Taylor–Couette flow

et al. 2014

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Direct numerical simulations of Taylor-Couette flow (TC), i.e. the flow between two coaxial and independently rotating cylinders were performed. Shear Reynolds numbers of up to 3 · 10 5 , corresponding to Taylor numbers of T a = 4.6 · 10 10 , were reached. Effective scaling laws for the torque are presented. The transition to the ultimate regime, in which asymptotic scaling laws (with logarithmic corrections) for the torque are expected to hold up to arbitrarily high driving, is analysed for different radius ratios, different aspect ratios and different rotation ratios. It is shown that the transition is approximately independent of the aspect-and rotation-ratios, but depends significantly on the radius-ratio. We furthermore calculate the local angular velocity profiles and visualize different flow regimes that depend both on the shearing of the flow, and the Coriolis force originating from the outer cylinder rotation. Two main regimes are distinguished, based on the magnitude of the Coriolis force, namely the co-rotating and weakly counter-rotating regime dominated by Rayleigh-unstable regions, and the strongly counter-rotating regime where a mixture of Rayleigh-stable and Rayleigh-unstable regions exist. Furthermore, an analogy between radius-ratio and outer-cylinder rotation is revealed, namely that smaller gaps behave like a wider gap with co-rotating cylinders, and that wider gaps behave like smaller gaps with weakly counter-rotating cylinders. Finally, the effect of the aspect ratio on the effective torque versus Taylor number scaling is analysed and it is shown that different branches of the torque-versus-Taylor relationships associated to different aspect ratios are found to cross within 15% of the Reynolds number associated to the transition to the ultimate regime. The paper culminates in phase diagram in the inner vs outer Reynolds number parameter space and in the Taylor vs inverse Rossby number parameter space, which can be seen as the extension of the Andereck et al. (J. Fluid Mech. 164, 155-183, 1986) phase diagram towards the ultimate regime.

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“…Shear stresses relative to TCN1 are significantly lower than the one associated with TCN2 both for intact and etched fiber. Except the axial pressure gradient due to gravity (equal in the two cases), there are no other external axial pressure gradients acting on the system that can induce torque reductions [21]. Differences on shear stresses are only ascribable to the different rotation regimes.…”

Section: Variation Of Flow Regimes For Tcn1 and Tcn2 Due To Fiber Etcmentioning

confidence: 99%

On the CFD Analysis of a Stratified Taylor-Couette System Dedicated to the Fabrication of Nanosensors

Griffini

Insinna

Salvadori

et al. 2017

Fluids

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Abstract:Since the pioneering work of Taylor, the analysis of flow regimes of incompressible, viscous fluids contained in circular Couette systems with independently rotating cylinders have charmed many researchers. The characteristics of such kind of flows have been considered for some industrial applications. Recently, Taylor-Couette flows found an innovative application in the production of optical fiber nanotips, to be used in molecular biology and medical diagnostic fields. Starting from the activity of Barucci et al., the present work concerns the numerical analysis of a Taylor-Couette system composed by two coaxial counter-rotating cylinders with low aspect ratio and radius ratio, filled with three stratified fluids. An accurate analysis of the flow regimes is performed, considering both the variation of inner and outer rotational speed and the reduction of fiber radius due to etching process. The large variety of individuated flow configurations provides useful information about the possible use of the Taylor-Couette system in a wide range of engineering applications. For the present case, the final objective is to provide accurate information to manufacturers of fiber nanotips about the expected flow regimes, thus helping them in the setup of the control process that will be used to generate high-quality products.

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Torque reduction in Taylor–Couette flows subject to an axial pressure gradient

Cited by 13 publications

References 43 publications

Numerical modelling of rotor–stator interaction in rim driven thrusters

Numerical modelling of rotor–stator interaction in rim driven thrusters

Exploring the phase diagram of fully turbulent Taylor–Couette flow

On the CFD Analysis of a Stratified Taylor-Couette System Dedicated to the Fabrication of Nanosensors

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