Taylor-Couette System Research Articles

Flow structures and heat transport in Taylor–Couette systems with axial temperature gradient

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Turbulence generation and decay in the Taylor–Couette system due to an abrupt stoppage

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Bubbles injection effect on Taylor–Couette flow controlled by deformations of inner cylinder cross-section

A numerical simulation is carried out to make investigation of bubbles interactions when injected in Taylor–Couette system. This process can affect the flow patterns, especially when it is combined with inner cylinder cross-section oscillations. The included phase is modeled by the Lagrangian approach. The flow regime range is considered until the onset of the wavy Taylor vortex flow (low regime). We attempt to characterize bubbles dispersion effects on the drag force near the inner-cylinder while it is executing radial sinusoidal deformations. It is assumed that the obtained configurations of air-bubbles accumulations are compared for validation with experimental and numerical studies from the literature. The bubbles have uniform spherical shape with a diameter Db = 0.06d, where d is the system gap width. The inner cylinder oscillation is imposed using a sinusoidal law with a fixed deforming frequency and different amplitude ratios of the initial radius R1. Overall, without reaching a fully developed regime, the obtained results for a low Taylor number showed that the drag reduction ratio could be decreased when the inner cylinder is deformed.

Use of SiO2 Nanoparticles in Water-Based Drilling Fluids for Improved Energy Consumption and Rheology: A Laboratory Study

Summary In wellbore drilling, it is appreciable to devise methods to study the rheology of high-speed annulus fluid flows. In this paper, a high-speed Taylor-Couette system (TCS) was devised to explore non-Newtonian fluid flow behavior appraised by SiO2 nanoparticles toward friction reduction, power saving, and rheology modeling of nanofluids. Water-based mud (WBM) as an environmentally friendly drilling fluid is investigated by adding SiO2 nanoparticles at four low-volume concentrations of 0.05, 0.1, 0.5, and 1% at speeds from 0 to 1,600 rev/min with 200 rev/min intervals in the TCS. Five rheology models based on the Herschel-Bulkley-Extended (HBE) model and a generalized Reynolds number were optimized to fit with the experimental data. All models except the Newtonian model have fitted all nanofluids with high accuracy, especially Bingham and HBE models. Negative deviation from Darcy friction was avoided for power-law (PL) and Herschel-Bulkley (HB) models using the modification to the generalized Reynolds number. Higher energy saving and enhanced rheology is reported particularly at lower volume concentrations of SiO2 WBM nanofluids. The Darcy friction factor deviated from laminar flow at the generalized Reynolds number beyond 2,000 into turbulent, which is a good indicator for the flow condition of complex non-Newtonian nanofluids in real-life application.

Experimental study on energy saving and friction reduction of Al2O3-WBM nanofluids in a high-speed Taylor-Couette flow system

In this work, a high-speed Taylor-Couette system (TCS) was developed for studying drilling fluids at rotational speeds from 0 to 1600 RPM. Water-based mud (WBM) drilling fluid is investigated here by adding Al2O3 nanoparticles at four low volume concentrations percentage of 0.05, 0.1, 0.5 and 1. Five rheology models including Newtonian, Power law, Bingham, Herschel-Bulkley (HB) and Herschel-Bulkley-Extended (HBE) were optimized to fit with the measured data. For Al2O3 nanofluids especially at lower volume concentrations, considerable power saving is observed. Results indicate that Bingham and HBE models fit precisely Al2O3 nanofluids data. Darcy friction factor is deviated from laminar flow at the generalized Reynolds number larger than 2000 for the preferred models. Negative deviation from laminar friction factor was observed.

Controlling the number of vortices and torque in Taylor–Couette flow

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Experimental Investigations on the Effect of Axial Homogenous Magnetic Fields on Propagating Vortex Flow in the Taylor-Couette System.

Experimental investigations of propagating vortex flow states (pV states) in a short Taylor–Couette system with asymmetric boundary conditions are presented. The flow state was established in a ferrofluid showing no magneto-viscous effect and was exposed to axial magnetic fields. It was found that the magnetic field led to a change in the spatial and temporal behavior of the pV state, indicating complex interactions between the flow field and magnetic field. A stepwise applied axial magnetic field destabilized the pV state, leading to an intermittent flow state. Gradually increasing the axial magnetic fields changed the temporal behavior of the regime. Up to magnetic field strengths of 20 kA/m, the orbital frequency, as a measure for the temporal periodicity, was increased with field strength.

Large-eddy simulation of counter-rotating Taylor–Couette flow: The effects of angular velocity and eccentricity

In the present work, turbulent flow in the annulus of a counter-rotating Taylor-Couette (CRTC) system is studied using large-eddy simulation. The numerical methodology employed is validated, for both the mean and second-order statistics, with the direct numerical simulation (DNS) data available in the literature, for a range of Reynolds numbers from 500 to 4000. Thereafter, turbulent flow occurring in this system at Reynolds numbers of 8000 and 16000 are studied, and the results obtained are analyzed using mean and second-order statistics, vortical structures, velocity vector plots and power energy spectra. Further, the spatio-temporal variation of azimuthal velocity, extracted near the inner cylinder, shows the existence of herringbone like patterns similar to that observed in the previous studies. The effect of eccentricity of the inner cylinder with respect to the outer cylinder is studied, on the turbulent flow in the CRTC system, for two different eccentricity ratios of 0.2 and 0.5 and for two different Reynolds numbers of 1500 and 4000. The results of the eccentric CRTC are analyzed using contours of pressure, mean and second-order statistics, velocity vectors, vortical structures, and turbulence anisotropy maps. It is observed from the eccentric CRTC simulations that the smaller-gap region seems to contain higher amplitude fluctuations and more vortical structures when compared with the larger-gap region. The mean turbulent kinetic energy contours do not change qualitatively with the Reynolds number, however, quantitatively a higher turbulent kinetic energy is observed in the higher Reynolds number case of 4000.

Numerical study of heat transfer in a Taylor-Couette system with forced radial throughflow

A modified configuration of the Taylor-Couette system with an imposed radial flow through the surfaces of a rotating inner cylinder and fixed outer one is considered. Numerical simulations of heat transfer in the annular gap were performed for a wide range of throughflow intensity and rotation rate. The regularities of the factors effect on the surface averaged Nusselt number and peculiarities of temperature distribution along the heated surface of the inner cylinder were obtained. The configuration of the inner rotating cylinder with longitudinal porous slots was considered and the influence of the slots number on heat transfer efficiency was examined. The main heat transfer parameters were compared to the ones calculated for the opened Taylor-Couette system with a forced axial flow. The efficiency of the radial throughlow configuration with regard to rotor cooling was shown to be significantly greater than in the case of the axial flow configuration. For instance, the maximum average surface Nusselt number is nearly 50% higher and the maximum local surface overheating is about 50% less. The new fundamental database obtained displays also the influence of turbulence development in the rotating subcritical boundary layer on the surface heat transfer.

Experimental Investigation on Rotating Electrochemical Etching of a Micro Spiral Cylindrical Electrode.

To realize the electrochemical etching of a micro spiral cylindrical electrode, a new method of rotating electrochemical etching is proposed, and its process is further studied. First, according to the electrochemical etching principle, the machining mechanism of rotating electrochemical etching of a micro spiral cylindrical electrode is introduced. Second, based on the spiral vortex theory in the Taylor-Couette system, the effect of the high-speed rotating cylindrical microelectrode on its external flow field is analyzed. Third, the effects of rotation direction, rotation speed, machining voltage, and machining time on the thread structure are analyzed by experiments. Finally, a spiral cylindrical microelectrode with good surface thread shape is fabricated within two minutes by using the optimized machining parameters. It is proved that the rotating electrochemical etching method is an easy way to fabricate a micro spiral cylindrical electrode with high efficiency and low cost.

Origin of localized snakes-and-ladders solutions of plane Couette flow.

Spatially localized invariant solutions of plane Couette flow are organized in a snakes-and-ladders structure strikingly similar to that observed for simpler pattern-forming partial differential equations [Schneider, Gibson, and Burke, Phys. Rev. Lett. 104, 104501 (2010)PRLTAO0031-900710.1103/PhysRevLett.104.104501]. We demonstrate the mechanism by which these snaking solutions originate from well-known periodic states of the Taylor-Couette system. They are formed by a localized slug of wavy-vortex flow that emerges from a background of Taylor vortices via a modulational sideband instability. This mechanism suggests a close connection between pattern-formation theory and Navier-Stokes flow.

Experimental investigation of energy dissipation in the multi-cylinder Couette-Taylor system with independently rotating cylinders

The paper presents the results of an experimental study of the process of dissipative heating of fluid in a multi-cylinder Couette-Taylor system with independently rotating smooth cylinders. The task was set to solve the problem of direct conversion of wind energy into heat. The flow regimes and generation of heat energy at relatively low cylinder revolutions F < 5 Hz were studied. This range corresponds to velocities of cylinder rotation, achieved by the wind turbine at moderate wind load. Rotation of only one cylinder with the braked second cylinder and their counter-rotation are considered. The second regime can be successfully implemented in the schemes of kinetic wind energy conversion without additional mechanical transmissions and reduction gears from two wind wheels. Water-glycerine solutions in a wide range of changes in their viscosity were used as a working fluid. It is shown that the specific thermal power released in the heat generator can be about 1 MW/m3, and this indicates the competitiveness of such devices among the designs of renewable energy resources.

CFD analysis of the hydrodynamic characteristics of an eccentric shaft in a canned motor

Boiler water circulation pump is the core of the 600MW and above supercritical boiler start system and the subcritical boiler furnace forced circulation system. A pressure fluctuation with the same frequency as shaft rotation was found during the use of a boiler water circulation pump at its outlet. Based on an engineering problem, the effects of eccentricity with axial flow on the hydrodynamic characteristics of the Taylor-Couette system is numerically studied in a simplified shaft system of canned motor, by using RNG k-ε turbulence model to solve the near-wall region more accurately. Sliding mesh is used to calculate the hydrodynamic balance of the shaft. Results show that the fluctuation rule of pressure in the entire shaft system is quite consistent. The pressure loss increases along the axial flow, and finally there is no pressure fluctuation at the outlet.

Resistance force pulsations of annular flow in the Couette-Taylor system with counter-rotating cylinders

The paper presents the results of an experimental study of the Couette-Taylor flow fluctuations in a ring channel with oppositely rotating multicylinder rotors. Experiments were carried out using water-glycerine solutions as a working fluid. The rotation resistance moment and its pulsations were investigated, using the system for measuring the torque resistance of rotation of rotors, made in the form of a digital dynamometer based on a tension sensor. The investigations made it possible to establish that the classic dependence of the appearance of Taylor vortices is observed in the slit flow of a multicylinder system rotating oppositely. It was shown that in the range of Reynolds numbers Re = (100 – 500), pulsations of dissipative processes with variable frequency and amplitude up to 10% of the mean value of rotation resistance are observed.

Numerical investigation of the effect of different working fluids on the pattern formation in a narrow rotating annulus

Fluid evolving in an annular gap between two coaxial cylinders, well known as Taylor–Couette flow, is one of the fundamental problems in fluid mechanics for the study of instabilities and the transition to turbulence. This flow system is typically a closed environment, where the working fluid is confined axially by end-plates and radially between the cylinders. In this work, we investigate, via CFD simulation, the influence of the working fluids confined inside an infinite aspect ratio Taylor–Couette system on the onset of cellular pattern. The inner cylinder rotates freely about a vertical axis through its centre, while the outer one, the upper and bottom end-caps are held at rest. The basic system is characterized by a height H = 150 mm, an annular gap d = 5 mm, a ratio of the inner to the outer cylinders radii η = 0.909, an aspect ratio corresponding to the cylinders height reported to the gap length Γ = 30 and a ratio of the gap to the radius of the inner cylinder δ = 0.1. The flow behaviour and the time-independent formation of axisymmetric vortices are investigated under steady-state condition. The main goal of this work is to show how the change in cellular pattern operates when changing the working fluid by simulating and comparing four different liquids, namely hydrogen, helium, lithium and water. Particular attention is given to the onset of Taylor vortices in the vicinity of the threshold of transition, i.e. from the laminar Couette flow to the occurrence of Taylor vortex flow. In addition, the flow patterns are presented in terms of distributions of wall shear stress, skin friction coefficient, streamlines and velocity components. The computed results show that the critical Taylor number for the different liquids is the same, Tac1 = 42.4. Interestingly, lithium and hydrogen exhibit quite different behaviours than other liquids. The shape and wavelength of Ekman cells and the Taylor vortices for lithium and hydrogen show significant changes compared to water and helium.

Investigation of the effect of small bubbles on energy dissipation in a vertical Couette–Taylor system

The effect of small bubbles on reduction of energy dissipation has been numerically investigated in a vertical Couette–Taylor system. Flow is in the annular space between two concentric cylinders as the internal cylinder is rotating while the outer cylinder is stationary. Main fluid between cylinders is silicone, while air bubbles are constantly injected into the main flow at the bottom of cylinders’ gap. The air bubbles rise through the flow when they are injected into the silicone flow. The flow is fully turbulence and Taylor vortices have appeared in the annulus gap. The rotational Reynolds number (Reω) varies from 700 to 3000. The fully two-phase turbulent flow has been studied using a discrete phase model and Euler–Lagrange approach. Air bubbles distribution or bubbles pattern through the main flow, which is acquired using numerical method, shows a good agreement to those acquired via experimental data in all Reynolds numbers. To investigate the changes of skin friction drag, the rate of energy dissipation in the system is calculated. The effect of injected air with constant flow rate on the total energy dissipation rate and the drag coefficient is also investigated. The results confirmed reduction of energy dissipation and about 25% of drag reduction when small bubbles were injected in the system. This reduction was the effect of the bubbles on the density of fluid and transformed momentum. Moreover, the acquired numerical results were in good agreement with those found in the previous experimental works, in which maximum Reω is up to 3000.

Tertiary and Quaternary States in the Taylor-Couette System

The analysis of the Taylor-Couette problem in the small gap limit is extended to the cases of tertiary and quaternary solutions. The theoretical results are compared with experimental observations. Although in the latter the small-gap approximation is not always well approximated, the comparison of theoretical results and observations yields reasonable agreements. The absence of the wavy twist mode in the observed patterns is explained by the presence of no-slip boundary conditions in the axial direction of the experimental apparatus, which differ from the periodic conditions imposed in the theoretical analysis. Quaternary solutions bifurcating from the tertiary ones through subharmonic instabilities are presented and compared with experimental observations. Reasonable agreement has been found.

Wall roughness induces asymptotic ultimate turbulence

Turbulence is omnipresent in Nature and technology, governing the transport of heat, mass, and momentum on multiple scales. For real-world applications of wall-bounded turbulence, the underlying surfaces are virtually always rough; yet characterizing and understanding the effects of wall roughness for turbulence remains a challenge, especially for rotating and thermally driven turbulence. By combining extensive experiments and numerical simulations, here, taking as example the paradigmatic Taylor-Couette system (the closed flow between two independently rotating coaxial cylinders), we show how wall roughness greatly enhances the overall transport properties and the corresponding scaling exponents. If only one of the walls is rough, we reveal that the bulk velocity is slaved to the rough side, due to the much stronger coupling to that wall by the detaching flow structures. If both walls are rough, the viscosity dependence is thoroughly eliminated in the boundary layers and we thus achieve asymptotic ultimate turbulence, i.e. the upper limit of transport, whose existence had been predicted by Robert Kraichnan in 1962 (Phys. Fluids {\bf 5}, 1374 (1962)) and in which the scalings laws can be extrapolated to arbitrarily large Reynolds numbers.

Balanced 20-kA DC Distributor for Magnetized Taylor Couette Systems, Utilizing Thermostatic Controlled Water Valves With CO2Adsorption Charge Sensors as Current Controller

A quasi-coaxial system consisting of a central current carrying copper rod and five symmetric return paths takes up to 20 kA. The installation provides a homogeneous magnetic field $\mathbf {B_{\varphi }}$ to a Taylor–Couette flow. One challenging part of the system is the design of the current distributor, which is supposed to divide the return current into several equally weighted lines. The individual components like the copper rods as well as all electrical contacts provide a characteristic resistance, each in the same magnitude of several $ {\mu }\Omega $ . By initial installation this will support an imbalance in the current distribution affecting the symmetry of the magnetic field. So the adjustment of current distribution becomes mandatory to ensure maximum field homogeneity. Controlling the outflow temperature of the required water cooling offers an indirect access to set the current by thermostatically operated valves with CO2 adsorption charge in conjunction with the temperature dependent branch resistance. A numerical investigation proves that a stable current distribution can be achieved by a couple of paralleled thermal controlled heater valves with proportional characteristics. Finally, recent ironless Hall-effect current sensors help to calibrate the system so that the current homogeneity differs less than 1% from optimal state in a wide range of currents.

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

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.