Taylor-Couette System Research Articles

Forced flow reversal in ferrofluidic Couette flow via alternating magnetic field

Time-dependent boundary conditions are very common in natural and industrial flows and by far no exception. An example of this is the movement of a magnetic fluid forced due to temporal modulations. In this study, we used numerical methods to examine the dynamics of ferrofluidic wavy vortex flows (WVF2, with dominant azimuthal wavenumber m=2) in the counter-rotating Taylor–Couette system, which was subjected to time-periodic modulation/forcing in a spatially homogeneous magnetic field. In the absence of a magnetic field, all WVF2 states move in the opposite direction to the rotation of the inner cylinder, they are retrograde. However, when strength or frequency of the alternating magnetic field increases, the motion direction of the flow pattern changes. Thus, the alternating field provides a precise and controllable key parameter for triggering the system response and controlling the flow. Aside, we also observed intermittent behavior when one solution became unstable, leading to random transitions in both, the transition time and toward the different final solutions. Our findings suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which may have applications in the development of modern fluid devices in laboratory experiments. These findings provide a framework to study other types of magnetic flows driven by time-dependent forcing.

Sustainable drag reduction in Taylor-Couette flow using riblet superhydrophobic surfaces

Superhydrophobic surfaces (SHSs) have been proven effective in reducing frictional drag force in various flow conditions. However, at high flow speeds, the air plastron on these surfaces collapses, leading to a decline in their effectiveness. In this study, we investigated the frictional drag forces of various SHSs and their combination with surface patterns across a wide range of flow conditions (5.00×102 < Re < 1.12×105) by using an facile coating method. Our experiments involved incorporating a superhydrophobic coating on the inner cylinder of a custom-made Taylor-Couette apparatus, integrated with a rheometer to measure torque applied on the inner rotor as a function of rotational speed. As part of our research, we calculate the effective slip length to assess the drag reduction performance of coatings, revealing an effective slip length of around 63 µm on a flat SHS. Furthermore, we explore the combined effect of superhydrophobic coatings and triangular-shaped riblets on drag reduction in Taylor-Couette flow, comparing the performance of these surfaces based on the riblet’s sharpness and the Reynolds number. Our experimental results show a reduction in measured torque of up to 24 % and 48 % on a V-grooved SHS in laminar and turbulent flow, respectively. Longevity tests confirm that the designed surfaces maintain their superhydrophobicity and drag reduction performance under turbulent flow conditions. Overall, this work introduces a passive drag reduction strategy through surface design, which substantially mitigates the frictional drag force and demonstrating considerable potential for enhanced performance and increased efficiency of Taylor-Couette systems.

Numerical Approach of the First Instability Appearance in Inclined Taylor–Couette System

The present study numerically investigates the three-dimensional forced and mixed convection heat transfer in an inclined Taylor–Couette system (η=0.5 and Γ=20) submitted to a radial temperature gradient. The main objective of this study is to determine the effect of the angle inclination duct on the thermal and dynamic fields. Several cases have been dealt with depending on the inclination angle to detect the critical Reynolds number in each case. The model of the conservation equations with their boundary conditions is numerically solved by the finite volume method with a second-order spatiotemporal discretization. The results show that, in forced convection, the effect of the inclination angle is inexistent on the velocity field. However, with the presence of buoyancy effects, which impact flow stability and the transition to turbulence, the inclination influences both velocity and temperature fields. It also shows that selecting the vertical position of the annulus is preferable to obtain hydrodynamic stability in mixed convection. At the same time, from the thermal point of view, it is preferable to select the horizontal position to get dynamic and thermal stability.

Exploring the rheology characteristics of Flowzan and Xanthan polymers in drilling water based fluids at high-temperature and high-shear rates

The study of drilling fluid behaviour across various temperature conditions is of paramount importance for industries such as oil and gas extraction, mineral exploration, and large-scale construction projects. To address this need, a custom-designed viscometer known as the Australian University of Kuwait Taylor-Couette System (AUTCS) was developed. The AUTCS apparatus incorporates a Taylor-Couette system, consisting of two co-axial cylinders with a testing liquid capacity of 100 ml. The inner cylinder can be rotated at speeds ranging from 0 to 3000 rpm. This configuration provides an economical testing system that is particularly suitable for studying expensive drilling fluids. To investigate high-temperature (HT) conditions, the apparatus is equipped with a controllable heating film jacket capable of warming fluids up to 350 F. One specific area of interest in the drilling industry is the exploration of less commonly used polymers, such as Flowzan and Xanthan, in water-based mud (WBM). Flowzan has gained increasing attention due to its potential applications in drilling fields. To facilitate the study of Flowzan and Xanthan, the AUTCS viscometer was fine-tuned using the standard conventional lab viscometer, FANN, that has limitations in terms of rotational speed range (0–600 RPM) and temperature range. The rheology characteristics of Flowzan and Xanthan including consistency charts, viscosity, and darcy friction factor are obtained and presented at temperatures of 79 F, 104 F, and 150 F, across a range of speeds from 0 to 3000 RPM. The findings were examined across several correlation functions. It is found that the Herschel–Bulkley model best represent Flow Zan and Xanthan polymers. These correlations contribute to a comprehensive understanding of the new polymers’ performance under different temperature and speed conditions in drilling applications.

Taylor Nearly Columnar Vortices in the Couette–Taylor System: Transition to Turbulence

Taylor Nearly Columnar Vortices in the Couette–Taylor System: Transition to Turbulence

Controlling Couette flow by alternating axial mass flux

This paper presents numerical simulations of the Taylor vortex flow under the influence of an externally applied alternating axial mass flux (through-flow) in a Taylor–Couette system with axial periodic boundary conditions. Such an axially modulating flow can lead to a significant variation in the onset of primary instabilities. Depending on the system parameters, the effect can be both stabilizing and destabilizing, i.e., shifting the bifurcation threshold to larger or smaller control parameters, respectively. It is found that the system response around the primary instability is sensitive to and critically influenced by an alternating mass flux, particularly the modulation frequency. We show that such an alternating axial flow represents an easily and, more importantly, precisely controllable key parameter to change the nonlinear system response from subcritical to supercritical behavior and vice versa. Furthermore, we observe different parameter regimes with regular and irregular intermittent flow dynamics.

Rheology of dilute bubble suspensions in unsteady shear flows

The viscoelasticity of a dilute bubble suspension is theoretically derived from the constitutive equation originally for a dilute emulsion proposed by Frankel &amp; Acrivos (J. Fluid Mech., vol. 44, issue 1, 1970, pp. 65–78). Non-dimensionalization of the original tensor equation indicates that the viscoelasticity is systematized for a given void fraction by the capillary number $Ca$ and dynamic capillary number $Cd$ , representing the bubble deformability and unsteadiness of bubble deformation. Comprehensive evaluation of the viscoelasticity according to the volume fraction, $Ca$ and $Cd$ reveals that whether the viscosity increases or decreases depends on whether $Ca$ or $Cd$ exceeds a common critical value. In addition, it is indicated that the bubble suspension has the most prominent viscoelasticity when the time scale of the shear deformation is the same as the relaxation time of the suspended bubble and when the bubbles keep a spherical shape, that is, $Ca \ll 1$ and $Cd = 1$ . The applicability of this theory in flow prediction was examined in a Taylor–Couette system, and experimentally good agreement was confirmed.

Effect of ribbing of the internal rotating cylinder in the Couette–Taylor system on the value of rotational resistance moment

Effect of ribbing of the internal rotating cylinder in the Couette–Taylor system on the value of rotational resistance moment

Spectral method for identification of flow regimes in a Couette-Taylor annular flow

The paper presents a study of flow structure in an annular flow of the Couette-Taylor system, employing spectral analysis of moment of resistance and radial dynamic pressure pulsations. Experiments were conducted on a model featuring a single annular gap, with the Reynolds number varied from 582 to 4271. A methodology for the digital recording of flow parameters was devised, comprising the measurement of the moment of resistance to rotation and radial pressure through the application of a strain gauge dynamometer, hydrophone and pressure transducer. The subsequent analysis of the obtained amplitude-frequency spectra enabled the identification of three distinctive ranges of pulsations, which were found to be associated with the relief of the cylinder surface, laminar flow with Taylor vortices and the turbulent regime.

Numerical Study of the Effect of a Power-law Fluid Flow Structures on Levels of Mixing in a Taylor Couette Configuration

This work is a numerical study on the effects of the flow structures of the power-law fluid between two concentric cylinders with an upward laminar axial flow on levels of mixing and mean residence time through the Taylor Couette system. The cylindrical annular duct presents a radius ratio of 0.5 and an aspect ratio of 8. The inner cylinder is rotating while the outer one is kept at rest. The residence time distributions (R.T.D.) method and the mean residence time (Tm) are used to determine the number of tanks in series and the dispersion coefficient to evaluate levels of mixing. To this end, a pulsed input injection of a tracer is computing at the outlet of the annulus. As a main objective of this study, is to analyze the effect of the flow structure of a power-law fluid between two concentric cylinders on the mixing level and mean residence time in a Taylor Couette system. The novelty of our work is the use of power-law fluids as particles-carrying fluids. Several parameters, such as the axial Reynolds number (Re), the Taylor number (Ta), and the power-law index behavior (n), are used to show their impact on levels of mixing. It is shown that when n increases, the number of stirred tanks in series N increases for pseudoplastic fluids (n&lt;1), indicating low levels of mixing while the parameter (N) decreases for dilatants fluids (n&gt;1), revealing high levels of mixing. The increase of the power-law index in the range of 0.6&lt;n&lt;1 decreases the dispersion coefficient, indicating the non-ideal mixing in the duct. In addition, for further increase of the power-law index in the range of n&gt;1 increases the dispersion coefficient points to the well-mixing.

Pattern Competition for the Sequential Bifurcations Approach (SBA) to Turbulence in the Co-Rotating Taylor–Couette System: Quinary States

Pattern Competition for the Sequential Bifurcations Approach (SBA) to Turbulence in the Co-Rotating Taylor–Couette System: Quinary States

Taylor-Couette flow in the narrow-gap limit.

A Cartesian representation of the Taylor-Couette system in the vanishing limit of the gap between coaxial cylinders is presented, where the ratio, [Formula: see text], of the angular velocities, [Formula: see text] and [Formula: see text], of the inner and the outer cylinders, respectively, affects its axisymmetric flow structures. Our numerical stability study finds remarkable agreement with previous studies for the critical Taylor number, [Formula: see text], for the onset of axisymmetric instability. The Taylor number [Formula: see text] can be expressed as [Formula: see text], where [Formula: see text] (the rotation number) and [Formula: see text] (the Reynolds number) in the Cartesian system are related to the average and the difference of [Formula: see text] and [Formula: see text]. The instability sets in the region [Formula: see text], while the product of [Formula: see text] and [Formula: see text] is kept finite. Furthermore, we developed a numerical code to calculate nonlinear axisymmetric flows. It is found that the mean flow distortion of the axisymmetric flow is antisymmetric across the gap when [Formula: see text], while a symmetric part of the mean flow distortion appears additionally when [Formula: see text]. Our analysis also shows that for a finite [Formula: see text] all flows with [Formula: see text] approach the [Formula: see text] axis, so that the plane Couette flow system is recovered in the vanishing gap limit. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (Part 2)'.

Solitary-like and modulated wavepackets in the Couette-Taylor flow with a radial temperature gradient.

We have performed numerical and experimental studies of the flow in a large aspect ratio Couette-Taylor system with a rotating inner cylinder and a fixed radial temperature gradient. The base flow state is a superposition of an azimuthal flow induced by rotation and an axial large convective cell induced by the temperature gradient. For a relatively large temperature gradient, the rotation rate of the inner cylinder destabilizes the convective cell to give rise to travelling wave pattern through a subcritical bifurcation. This wave pattern is associated with a temperature mode and it consists of helical vortices travelling in the annulus. In a small range of the rotation rate, helical vortices have longitudinal meandering leading to the formation of kinks randomly distributed, leading to spatio-temporal disordered patterns. The flow becomes regular for a large interval of rotation rate. The friction, the momentum and the heat transfer coefficients are computed and found to be independent of the heating direction. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (part 1)'.

Computational modelling of turbulent Taylor–Couette flow for bearing chamber applications: A comparison of unsteady Reynolds-averaged Navier–Stokes models

The capability to accurately model fluid flow within rotating Taylor–Couette systems has a primary role in informing computational investigations of rotating machinery. There is considerable uncertainty regarding selection of modelling approach, including a suitable turbulence model, that can accurately resolve turbulence within such complex flows while remaining computationally feasible for industrially relevant applications. This paper presents a numerical comparison of axisymmetric and three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) turbulence models within ANSYS Fluent. The CFD geometries are representative of ones for which there are published experimental measurements. For the Taylor–Couette study, investigation into inner cylinder start-up procedure, based on previous published findings, confirmed that the final state of the flow is highly dependent on the initial conditions and acceleration rate. Once Taylor vortices form and stabilise, they are not disrupted by small steps in inner cylinder speed, allowing computationally efficient accelerations. Investigations into applying rotational periodicity were unsuccessful, resulting in a significantly reduced core velocity. Axisymmetric predictions provided reasonable agreement with experimental data only at low rotation rates. A good prediction of the velocity flow field was obtained for three-dimensional simulations of the full 360° domain with differences of less than 5% for radial velocities. Among the URANS models, the standard k-ω model and baseline Reynolds stress model (BSL-RSM) provided the closest agreement to published experimental data. In the paper, the developed Taylor–Couette turbulence modelling methodology is extended to a bearing chamber geometry. Analysis of the secondary vortex flow field is compared both qualitatively and quantitatively to published bearing chamber experimental measurements. Overall, whilst a good agreement is still found using the standard k-ω turbulence model, discrepancies arise with the BSL-RSM. However, for this more complex bearing chamber environment compared to a Taylor–Couette flow, the shear stress transport k-ω turbulence model provided the closest agreement and is recommended for future bearing chamber modelling.

Numerical study of frictional drag reduction using micro-bubbles in a vertical Couette-Taylor system

In this work, we numerically study the reduction of frictional drag in a vertical Couette-Taylor system by using micro-bubbles. The silicon flow is in the annular gap between two concentric cylinders as the internal cylinder is rotating while the outer cylinder is stationary. Taylor vortices are formed between the cylinders and the rotational Reynolds number also varies from 700 to 4500. The carrier flow is silicone while air bubbles are constantly injected into the carrier phase at the bottom of cylinders and rise through the flow. By employing a discrete phase model and Euler-Lagrange approach, we investigate a two-phase turbulent flow. In this way, we study the distribution of the bubbles through the flow, which is acquired using numerical modeling. Our numerical results are in good agreement with the experimentally reported data for different values of Reynolds numbers. We also investigate the effect of injected air with a constant flow rate on the skin friction drag and on the drag coefficient ratio. Our numerical results illustrate a reduction of drag about 36% when microbubbles are injected into the system. This reduction can be achieved by the effect of the bubbles on the density of the fluid and transformed momentum.

Thermomagnetic instability of a ferrofluid in a differentially heated Taylor-Couette system

Ferrofluids have a very wide range of possible values of Prandtl number since they are water-based or oil-based. Recent research has highlighted the important role played by the centrifugal buoyancy in highly viscous fluids. The present paper investigates the impact of the centrifugal buoyancy on the thermomagnetic instability in a ferrofluid confined in a cylindrical annulus with a rotating inner cylinder, with a special interest on the effect of viscosity.

Secondary instabilities in Taylor–Couette flow of shear-thinning fluids

The stability of the Taylor vortex flow in Newtonian and shear-thinning fluids is investigated in the case of a wide gap Taylor–Couette system. The considered radius ratio is$\eta = R_1/R_2=0.4$. The aspect ratio (length over the gap width) of experimental configuration is 32. Flow visualization and measurements of two-dimensional flow fields with particle image velocimetry are performed in a glycerol aqueous solution (Newtonian fluid) and in xanthan gum aqueous solutions (shear-thinning fluids). The experiments are accompanied by axisymmetric numerical simulations of Taylor–Couette flow in the same gap of a Newtonian and a purely viscous shear-thinning fluid described by the Carreau model. The experimentally observed critical Reynolds and wavenumbers at the onset of Taylor vortices are in very good agreement with that obtained from a linear theory assuming a purely viscous shear-thinning fluid and infinitely long cylinders. They are not affected by the viscoelasticity of the used fluids. For the Newtonian fluid, the Taylor vortex flow (TVF) regime is found to bifurcate into a wavy vortex flow with a high frequency and low amplitude of axial oscillations of the vortices at${Re} = 5.28 \, {Re}_c$. At${Re} = 6.9 \, {Re}_c$, the frequency of oscillations decreases and the amplitude increases abruptly. For the shear-thinning fluids the secondary instability conserves axisymmetry. The latter is characterized by an instability of the array of vortices leading to a continuous sequence of creation and merging of vortex pairs. Axisymmetric numerical simulations reproduce qualitatively very well the experimentally observed flow behaviour.

Onset of axisymmetric sloshing in a food processor.

We report on the axisymmetric oscillation at the air-water interface in a food processor and Taylor-Couette systems. To gain insights into the mechanisms of free-surface oscillation, we conduct a series of experiments on the visual observations of free-surface deformation and the velocity measurements. At relatively low rotation speeds, the surface height at the rotating object surface decreases but remains stationary. As the rotation speed increases in small increments, oscillation begins when the deformed free surface detaches from the rotating object, and its onset depends strongly on the initial surface height. To account for the similarity mechanism of the onset, a scaled surface deformation based on the bulk Froude number is introduced herein; we find that the oscillation occurs at the scaled surface deformation beyond unity. These findings explain the causal relationship between the surface deformation and the oscillation onset and help to predict its occurrence to avoid mechanical damage to an apparatus with rotating components.

Flow regimes in a multi-gap circular Couette-Taylor system with opposite rotating cylinders

This work investigates the flow structure in the gaps of a multi-cylinder circular Couette-Taylor system, which is a model of a two-rotor heat generator. The initial information for studying the flow structure was data on the magnitude of the resistance torque to rotors opposed rotation, as well as on the nature of the amplitude-frequency spectrum of pulsations of this torque, depending on the viscosity of the working fluid and the rotational speed of the heat generator rotors. The obtained data allow comparing the nature of hydrodynamic processes in the single and obtained multi-gap circular space of Couette-Taylor and calculating the parameters of structural formations in the multi-gap working space of the heat generator. At relative rotational speeds of rotors (3-50) rad/s, the main energy of flow pulsations (up to 90%) is found in the amplitude-frequency spectra in the frequency range (12-70) Hz. It is associated with vortices first described by Taylor, which are extended low-frequency regularly alternating spirals and vortex structures with right and left rotation in the region of higher frequencies (200– 500) Hz; their frequency is determined by the width of the annular gaps of the multi-cylinder system.

Simulation of Wellbore Drilling Energy Saving of Nanofluids Using an Experimental Taylor\u2013Couette Flow System

Power consumption of wellbore drilling in oil and gas exploitations count for 40% of total costs, hence power saving of WBM (water-based mud) by adding different concentrations of Al2O3, TiO2 and SiO2 nanoparticles is investigated here. A high-speed Taylor–Couette system (TCS) was devised to operate at speeds 0–1600 RPM to simulate power consumption of wellbore drilling using nanofluids in laminar to turbulent flow conditions. The TCS control unit uses several sensors to record current, voltage and rotational speed and Arduino microprocessors to process outputs including rheological properties and power consumption. Total power consumption of the TCS was correlated with a second-order polynomial function of rotational speed for different nanofluids, and the correlated parameters were found using an optimization technique. For the first time, energy saving of three nanofluids at four low volume concentrations 0.05, 0.1, 0.5 and 1% is investigated in the TCS simulating wellbore drilling operation. It is interesting to observe that the lower concentration nanofluids (0.05%) have better power savings. In average, for the lower concentration nanofluids (0.05%), power was saved by 39%, 30% and 26% for TiO2, Al2O3 and SiO2 WBM nanofluids, respectively. TiO2 nanofluids have better power saving at lower concentrations of 0.05 and 0.1%, while Al2O3 nanofluids have saved more power at higher concentrations of 0.5 and 1.0% compared with their counterpart nanofluids.