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Taylor-Couette-Poiseuille (TCP) flow, characterized by the flow through an inner rotating shaft and an outer stationary cylinder, is a fundamental flow system in many industrial applications, including ship stern tubes, turbomachinery, journal bearings, and offshore drilling. Understanding the hydrodynamics of the TCP flow offers significant benefits for ensuring the robust design and operational efficiency of such systems. This paper presents the numerical modeling of turbulent TCP flow to assess the combined effects of two key control parameters-axial Reynolds number (10000-30000) and Taylor number (2.2x107-3.1x109)-on the fluid dynamics within the system. Using Reynolds Stress Modeling, this study investigates the behavior of TCP flow at high Reynolds numbers, which is relevant to real-world rotating machinery. The results indicate that the interaction between rotation and axial flow is not linear, with high rotation rates showing distinct behavior from low rotation rates, especially in the throughflow effects. At low and moderate rotation numbers (N), both the mean and turbulent variables display strong dependence on the rotational velocity and axial flow rate. However, further increases in N lead the flow field to be increasingly dominated by the contribution of rotation, and mean flow variables become relatively independent of the imposed flow rate. Furthermore, systematic deviations from the log-law in the boundary layer velocity profiles further emphasize the need to account for the combined effects of rotation and axial flow in the TCP flow system design and operation.

In industrial applications, Taylor–Couette–Poiseuille (TCP) flows are usually characterized by limited axial scope and eccentricity. The aerodynamic and thermal performance characteristics of these flows strongly depend on the coupling between the end leakage and axial throughflow. This study addressed the flow field and convective heat transfer characteristics of limited-length TCP flows (limited TCP flows); the rotational Reynolds number ranged from 590 to 1110, eccentricity ratio ranged from 0.3 to 0.7, dimensionless clearance height ranged from 0.016 to 0.04, and axial Reynolds number ranged from 0 to 70. Axial throughflow induced upstream movement of the high-pressure zone and downstream movement of the low-pressure zone along the axial direction, constituting a novel finding. The shearing flow's static pressure was sinusoidal in the angular direction, with the maximum and minimum at θ = 0.73π and θ = 1.08π, respectively. For 0.375 < Z/L < 0.625, the line-averaged Nusselt number remained almost unchanged, whereas it increased sharply near the end of the clearance. The pressure and the Nusselt number increased as the rotational Reynolds number, eccentricity, and axial Reynolds number increased, and decreased as the dimensionless clearance height increased. At Rea = 80, axial throughflow dominated the limited TCP flow. Compared with the limited Taylor–Couette flow, the axial throughflow increased the initial pressure of the gas film. In the central section, the angular distance between the maximal and minimal static pressures was smaller than for limited Taylor–Couette flow. The pressure and Nusselt number curves for the limited TCP flow were center-asymmetrical. Within the parametric range considered in this study, the limited TCP flow was almost laminar in the clearance, while it is highly turbulent as approaching to. Taylor vortices emerged near the clearance inlet but disappeared near the clearance outlet, distinct from the limited Taylor–Couette flow. [ABSTRACT FROM AUTHOR]

A fully developed turbulent flow in a concentric annulus, Re =10,000, ri/ro=0.5, with an inner rotating cylinder in the velocity range N=Uω/Ub=0÷4, is studied via a large-eddy simulation. Also, for comparison, simulations by steady-state, unstatiounary RANS k-ω SST (URANS), and Elliptic Blending Model (EBM) were made. The main focus of this study is on the effect of high rotation on the mean flow, turbulence statistics, and vortex structure. Distribution of the tangential velocity and the Reynolds stress tensor change their behaviour at N>0.5∼1. With rotation increases, the production of tangential fluctuation becomes dominant over axial ones and the position of turbulent kinetic energy maximum shifts towards the wall into the buffer zone. URANS and EBM approaches show good agreement with LES in mean flow, turbulent statistics, and integral parameters. The difference in pressure loss prediction between LES and URANS does not exceed 20%, but the average difference is about 11%. The EBM approach underestimates pressure losses up to 9% and on average not more than 5%. Vortex structures are described well by URANS.

This paper presents the results of fluid flow and convection heat transfer in concentric and eccentric annuli between two cylinders using a three-dimensional computational fluid dynamics model. Effects of rotational speed ( n = 0, 150, 300, and 400 rpm) and eccentricity (ε = 0, 0.15, 0.3, 0.45, and 0.6) on axial and tangential velocity distribution, pressure drop and forced convection heat transfer are investigated for radii ratios (η) of 0.2, 0.4, 0.6, and 0.8, Reynolds number 2.0 × 10 3 –1.236 × 10 5 , Taylor number 1.47 × 10 6 –1.6 × 10 10 , and Prandtl number 3.71–6.94. The parameters cover many applications, including rotary heat exchangers, mixers, agitators, etc. Nusselt numbers and friction factors for stationary and rotated concentric and eccentric annuli are correlated with four dimensionless numbers. The results revealed that when the speed of the inner cylinder increases from 0 to 400 rpm, the friction factor increases by 7.7%–103% for concentric and 8.2%–148% for eccentric annuli, whereas Nusselt number enhances by 37%–333% for concentric and 44%–340% for eccentric annuli. The radius ratio has a substantial effect on the heat transfer and pressure drop in annuli. The eccentricity enhances the heat transfer up to 12%, whereas its effect on the friction factor is not monotonic as it depends on Reynolds number, radii ratios, and rotational speed.

Flow in a concentric annular passage with a rotating inner cylinder, which is called Taylor-Couette flow, is important in industrial applications, such as electric motor which requires not only effective cooling of rotating shaft but also saving power required for the axis rotation. When the through flow is superposed, which is called Taylor-Couette-Poiseuille flow, it affects the cooling efficiency and the torque required for the axis rotation. To the authors' knowledge, previous studies have been focused on either the Nusselt number or the torque coefficient in the Taylor-Couette-Poiseuille flow. Therefore, it is difficult to estimate the through-flow effects on both of them under the same geometry and flow conditions. In this study, the through-flow effects on both the Nusselt number and the torque coefficient in the Taylor-Couette-Poiseuille flow under the same geometry and flow conditions were investigated by performing large eddy simulation. The through-flow Reynolds number, Re, was varied from 500 to 8000 under constant Taylor and Prandtl numbers of Ta=4000 and Pr=0.71, respectively. The Nusselt number and the torque coefficient had similar trend to each other with the increase of Re. They decreased by 25% for the change of Re from 0 to 1000 and were nearly constant for the change of Re from 4000 to 8000. Contribution of the advection, turbulent transport and diffusion terms to the Nusselt number and the torque coefficient were evaluated by using the equations proposed by the authors. The contribution of the advection term was nearly zero for Re from 500 to 8000, which was contrary to the case without through-flow (Re=0). As Re increased, the contribution of the turbulent transport term decreased but that of the diffusion term did not change so much. The friction factor in the axial direction varied as Re-0.75 of which power was between laminar (Re-1) and turbulent (Re-0.25) correlations in a smooth stationary pipe flow.

We study the stationary Navier–Stokes equations in the region between two rotating concentric cylinders. We first prove that, for a small Reynolds number, if the fluid flow is axisymmetric and if its velocity is sufficiently small in the $L^\infty$ -norm, then it is necessarily the Taylor–Couette–Poiseuille flow. If, in addition, the associated pressure is bounded or periodic in the $z$ axis, then it coincides with the well-known canonical Taylor–Couette flow. We discuss the relation between uniqueness and stability of such a flow in terms of the Taylor number in the case of narrow gap of two cylinders. The investigation in comparison with two Reynolds numbers based on inner and outer cylinder rotational velocities is also conducted. Next, we give a certain bound of the Reynolds number and the $L^\infty$ -norm of the velocity such that the fluid is, indeed, necessarily axisymmetric. As a result, it is clarified that smallness of Reynolds number of the fluid in the two rotating concentric cylinders governs both axisymmetry and the Taylor–Couette–Poiseuille flow with the exact form of the pressure. [ABSTRACT FROM AUTHOR]

Flow patterns of a Taylor-Couette-Poiseuille flow were studied at low axial Reynolds and rotational Taylor numbers (Re ≤ 10.5, Ta ≤ 319). The radius ratio of the inner and outer cylinders was 0.804 and the ratio of the length of the annulus to the gap width was 44.5. Complete map of the studied flow regimes was elaborated. The axial and azimuthal components of the wall shear rate γ were measured at the outer fixed cylinder using a three-segment electrodiffusion probe. The components of the wall shear rate of helices have never been measured in previous investigations. Spatio-temporal description of multiple flow patterns was obtained using flow visualizations and simultaneous measurements of wall shear rate components. The flow structures include Taylor vortices, helices winding in the same direction as the base flow or in the opposite direction, helices that were stagnant or moving in the axial direction, smooth or with superposed azimuthal waves, among others. The influence of different flow structures on the wall shear stress components is discussed with and without axial base flow. It was found that the wall shear stress is a function of Ta but no significant dependence on Re was observed for the studied flow regimes and that the mean wall shear stress increases with the number of azimuthal waves. It was also noted that the ED probes provide a more detailed information about flow patterns than torque measurements and visualizations described in the literature.

Taylor-Couette-Poiseuille (TCP) flow, characterized by the flow through an inner rotating shaft and an outer stationary cylinder, is a fundamental flow system in many industrial applications, including ship stern tubes, turbomachinery, journal bearings, and offshore drilling. Understanding the hydrodynamics of the TCP flow offers significant benefits for ensuring the robust design and operational efficiency of such systems. This paper presents the numerical modeling of turbulent TCP flow to assess the combined effects of two key control parameters-axial Reynolds number (10000-30000) and Taylor number (2.2x107-3.1x109)-on the fluid dynamics within the system. Using Reynolds Stress Modeling, this study investigates the behavior of TCP flow at high Reynolds numbers, which is relevant to real-world rotating machinery. The results indicate that the interaction between rotation and axial flow is not linear, with high rotation rates showing distinct behavior from low rotation rates, especially in the throughflow effects. At low and moderate rotation numbers (N), both the mean and turbulent variables display strong dependence on the rotational velocity and axial flow rate. However, further increases in N lead the flow field to be increasingly dominated by the contribution of rotation, and mean flow variables become relatively independent of the imposed flow rate. Furthermore, systematic deviations from the log-law in the boundary layer velocity profiles further emphasize the need to account for the combined effects of rotation and axial flow in the TCP flow system design and operation. [ABSTRACT FROM AUTHOR]

We performed direct numerical simulations of Taylor–Couette–Poiseuille flows within an annular channel with a radius ratio of 0.883. A parametric study was conducted on subcritical transition processes of the wall-bounded combined shear flow with a torsional base-flow profile with three control parameters of F(P) representing the axial mean pressure gradient and two Reynolds numbers R e in and R e out , based on the inner cylinder and outer cylinder rotational velocities, respectively. In the set (R e in , R e out) = (400 , − 1000) , the laminar flow becomes turbulent via finite-length and infinite-length turbulent bands, called one-way helical turbulence, as F(P) increases. Two-way helical turbulence appeared in the counterpart of the annular Poiseuille flow without cylindrical rotations, suggesting that the azimuthal Couette flow broke the symmetry of the helical turbulence of the axial Poiseuille flow. In the set of (R e in , R e out) = (800 , − 2000) and (1200 , − 3000) , we found a ring-shaped localized turbulence at F(P) that provided an axial friction Reynolds number comparable to the azimuthal one. The flow states were mapped in parameter space spanned by the axial and azimuthal friction Reynolds numbers. Eight different flow regimes, including the laminar state, were identified based on turbulent statistics during these flow visualizations. [ABSTRACT FROM AUTHOR]

This study numerically investigates the effects of an abruptly contracting and expanding annular gap on the propagation of Taylor vortices in Taylor-Couette-Poiseuille flow. The results show that the pressure drop between the inlet and the outlet exhibits oscillations with low frequency and large amplitude. The nondimensional amplitude of oscillating pressure increases linearly with an increase in the rotating Reynolds number, whereas the nondimensional oscillating frequency remains nearly invariant with varying rotating and axial Reynolds numbers. Owing to the alternate action of counter-rotating Taylor vortex pairs in front of the block, local flow resistance periodically increases and decreases, resulting in the pressure drop oscillation. By analyzing the drift velocity and wavelength of the propagating Taylor vortex pair, a prediction model for the oscillating frequency is developed. Its results show that the nondimensional frequency is proportional to the blockage ratio. With an increase in the latter, the oscillating amplitude nonmonotonically changes as a result of the tunneling phenomenon, whereby the anticlockwise rotating Taylor roller is punctured by axial flow. Based on the above mechanism of pressure oscillation, the structure of a vortex breaker is proposed that can effectively reduce the oscillation in pressure. [ABSTRACT FROM AUTHOR]

A fully developed turbulent flow in a concentric annulus, Re = 10,000 , r i / r o = 0.5 , with an inner rotating cylinder in the velocity range N = U ω / U b = 0 ÷ 4 , is studied via a large-eddy simulation. Also, for comparison, simulations by steady-state, unstatiounary RANS k- ω SST (URANS), and Elliptic Blending Model (EBM) were made. The main focus of this study is on the effect of high rotation on the mean flow, turbulence statistics, and vortex structure. Distribution of the tangential velocity and the Reynolds stress tensor change their behaviour at N > 0.5 ∼ 1 . With rotation increases, the production of tangential fluctuation becomes dominant over axial ones and the position of turbulent kinetic energy maximum shifts towards the wall into the buffer zone. URANS and EBM approaches show good agreement with LES in mean flow, turbulent statistics, and integral parameters. The difference in pressure loss prediction between LES and URANS does not exceed 20%, but the average difference is about 11%. The EBM approach underestimates pressure losses up to 9% and on average not more than 5%. Vortex structures are described well by URANS. [ABSTRACT FROM AUTHOR]

The current work investigates the rate of cooling of an axial air flow through the gap between the stator and the rotor of a four-pole synchronous electric motor. The axial air is passing though the rotor's four longitudinal slots. The stator is considered insulated. The effect of the axial air flow rate, the rotor rotational speed and the slot size on the average Nusselt number has been investigated numerically using ANSYS-CFX. These effects have been studied considering a motor radius ratio (RR) in the range of 0.65–0.85, an axial Reynolds number (Rea) between 1750 and 40,000 and a rotational Reynolds number (Rer) of 1750 up to 35,000.Numerical results have been validated using published experimental data. The maximum deviation was less than 15 %. The present numerical results showed that increasing the axial air flow rate always enhances the rate of cooling. The effect of the axial Reynolds number was found to be more dominant than that of the rotational Reynolds number. Increasing the rotor rotational speed (Rer) enhanced the rate of heat transfer up to a certain limit beyond which a revered effect was observed. Such limit was investigated and found to depend on the motor radius ratio and the relative magnitude of the axial and rotational Reynolds numbers represented by X = Rea/Rer. The enhancement due to increasing Rer was reversed at X = 0.33 and 0.12 when RR was at 0.85 and 0.75, respectively. A new correlation of the average Nusselt number as a function of the axial and rotational Reynolds number has been developed.

In this article, we derive a rigorous characterization of the boundary-layer and interior separations in the Taylor–Couette–Poiseuille flow. The results obtained provide a rigorous characterization on how, when, and where the propagating Taylor vortices (PTVs) are generated. We consider only the narrow gap and axisymmetric case where a pressure gradient is applied along the axis where the cylinders rotate and where there are no radial motions. In this case, the governing equations are an approximation of the classical Bénard equations. In particular, contrary to what is commonly believed, in the case under consideration, we show that the PTVs do not appear after the first dynamical bifurcation, and they appear only when the Taylor number is further increased to cross another critical value so that a structural bifurcation occurs. This structural bifurcation corresponds to the boundary-layer and interior separations of the flow structure in the physical space. [ABSTRACT FROM AUTHOR]

The effect of radial flow injection on the heat transfer characteristics of a Taylor–Couette–Poiseuille flow in an annulus is numerically investigated using the SST k-ω turbulence model. The ranges of the axial Reynolds number (ReA) and the rotational Reynolds number (ReΩ) are 6.58 × 10 4 − 1.37 × 10 5 and 7.19 × 10 4 – 1.8 × 10 5 , respectively. For every combination of axial and rotational Reynolds number, flow is injected radially into the air gap through a rectangular duct located on the inner cylinder with the injection rate m ̇ i n j / m ̇ a x i a l which varies from 0.02 to 0.14. Airflow in the air gap, before the injection, is in a fully developed condition and the effect of radial injection on the heat transfer of inner and outer cylinder is investigated in terms of the Nusselt number. In the studied range, radial injection increases the averaged Nusselt number up to 24% on the inner cylinder and up to 27% on the outer cylinder. In order to compare the heat transfer increase due to the radial injection, Nu* is defined as the difference between local Nusselt and Nusselt number of the fully developed flow happening at the same configuration without injection, and it is shown that though the trend of local Nusselt on the inner and outer cylinder is different, the averaged Nu* on both surfaces follows the same trend. [ABSTRACT FROM AUTHOR]

Abstract Taylor–Couette–Poiseuille (TCP) flow dominates the inner water-cooling circulation of canned motor reactor coolant pumps. Current research on TCP flow focuses on torque behaviors and flow regime transitions through experiments and simulations. However, research on axial flow resistance in a large Reynolds number turbulent state is not sufficient, especially for the various flow patterns. This study is devoted to investigating the influence of annular flow on the axial flow resistance of liquid in the coaxial cylinders of the stator and rotor in canned motor reactor coolant pumps, and predicting the coolant flow distribution between the upper coil cooling loop and lower bearing lubricating loop for safe operation. The axial flow resistance, coupled with the annular rotation, is experimentally investigated at a flow rate with an axial Reynolds number, Re a, from 2.6 × 103 to 6.0 × 103 and rotational Reynolds number, Re t, from 1.6 × 104 to 4.0 × 104. It is revealed that the axial flow frictional coefficient varies against the axial flow rate in linear relation sets with logarithmic coordinates, which shift up when the flow has a higher Re t. Further examination of the axial flow resistance, with the Re a extending to 3.5 × 105 and Re t up to 1.6 × 105, by simulation shows gentle variation rates in the axial flow frictional coefficients against the Re a. The relation curves with different Ret values converge when the Re a exceeds 3.5 × 105. A prediction model for TCP flow consisting of a polygonal approximation with logarithmic coordinates is developed to estimate the axial flow resistance against different axial and rotational Reynolds numbers for the evaluation of heat and mass transfer during transition states and the engineering design of the canned motor chamber structure.

Flow patterns of a Taylor-Couette-Poiseuille flow were studied at low axial Reynolds and rotational Taylor numbers (Re ≤ 10.5, Ta ≤ 319). The radius ratio of the inner and outer cylinders was 0.804 and the ratio of the length of the annulus to the gap width was 44.5. Complete map of the studied flow regimes was elaborated. The axial and azimuthal components of the wall shear rate γ were measured at the outer fixed cylinder using a three-segment electrodiffusion probe. The components of the wall shear rate of helices have never been measured in previous investigations. Spatio-temporal description of multiple flow patterns was obtained using flow visualizations and simultaneous measurements of wall shear rate components. The flow structures include Taylor vortices, helices winding in the same direction as the base flow or in the opposite direction, helices that were stagnant or moving in the axial direction, smooth or with superposed azimuthal waves, among others. The influence of different flow structures on the wall shear stress components is discussed with and without axial base flow. It was found that the wall shear stress is a function of Ta but no significant dependence on Re was observed for the studied flow regimes and that the mean wall shear stress increases with the number of azimuthal waves. It was also noted that the ED probes provide a more detailed information about flow patterns than torque measurements and visualizations described in the literature. [ABSTRACT FROM AUTHOR]

Increasing power densities of electric machines in e-vehicles in addition to the resulting quest for enhanced cooling concepts are bringing forward the importance of defining adequate heat transfer correlations in air gaps. This is a highly challenging topic, as there exist no generally applicable flow and heat transfer phenomena descriptions for air gaps due to their highly variable geometrical properties and operating conditions. As an answer to this challenge, this paper presents a workflow that defines an adequate 3D CFD model for an arbitrary air-gap design that includes its system-dependent boundary conditions. The workflow is built on the recognition of underlying air-gap flow phenomena, which are used to steer the subsequent design of the 3D CFD model in a systematic step-by-step manner. Consequently, the complexity of the 3D CFD model gradually increases to the point where it provides an adequate flow and heat transfer description. Validation of the workflow is presented for a wide range of air-gap designs and flow conditions. It is demonstrated that the 3D CFD models obtained with the workflow match the experimentally obtained data from various flow cases that have been documented in the literature. Considerable optimization of computational costs, offering potentially an order-of-magnitude reduction in computational time, is achieved as a result of computational domain span optimization and transient simulations being applied only when required. The validation confirms that this workflow facilitates construction of valid 3D CFD models without the prior knowledge of flow and heat transfer phenomena in a specific air gap. This workflow thus provides a reliable and computationally efficient tool for valorization of convective heat transfer, and opens up prospects for time- and cost-efficient optimizations of electric machines’ cooling system designs.

Variations in the local stability of the flow in a Taylor-Couette cell can be imposed by adding an axial Poiseuille flow and a radial flow associated with one or both of the cylinders being permeable. At a given rotation rate of the inner cylinder, this results in adjacent regions of the flow that can be simultaneously stable, convectively unstable, and absolutely unstable, making this system fit for studying global modes of instability. To this end, building on the existing stability analysis in absolute modes developing over axially invariant base flows, we consider the case of axially varying base flows in systems for which the outer cylinder is impermeable, and the inner cylinder is a weakly permeable membrane through which the radial flow is governed by Darcy's law. The frameworks of linear and nonlinear global modes are used to describe the instabilities and assess the results of direct numerical simulations using a dedicated pseudospectral method. Three different axially evolving set-ups are considered. In the first, fluid injection occurs along the full inner cylinder. In the second, fluid extraction occurs along the full inner cylinder. Besides its fundamental interest, this set-up is relevant to filtration devices. In the third, fluid flux through the inner cylinder evolves from extraction to injection as cross-flow reversal occurs. In agreement with the global mode analyses, the numerical simulations develop centrifugal instabilities above the predicted critical rotation rates and downstream of the predicted axial locations. The global mode analyses do not fully explain, however, that the instabilities observed in the numerical simulations take the form of axial stacks of wavepackets characterized by jumps of the temporal frequency. [ABSTRACT FROM AUTHOR]

The combined effects of axial flow and eccentricity on the temporal stability properties of the Taylor–Couette system are investigated using a pseudospectral method. Eccentricity is found to stabilize the Couette flow regardless of axial advection intensity. As the axial Reynolds number ${\mathit{Re}}_{z} $ is increased for any fixed eccentricity $e\leq 0. 7$, the critical mode switches from deformed toroidal Taylor vortices to helical structures with an increasing number of waves, and with helicity opposed to the inner-cylinder rotation. For a wide-gap configuration of radius ratio $\eta = 0. 5$, increasing axial advection has a stabilizing effect for low ${\mathit{Re}}_{z} $, then a weak destabilizing effect for high enough ${\mathit{Re}}_{z} $. Centrifugal effects are always destabilizing, but axial shear is responsible for the dominance of helical modes of increasing azimuthal complexity. The modes localize in the converging gap region, and the energy concentrates increasingly into axial motion for larger ${\mathit{Re}}_{z} $. Critical quantities are also computed for a small-gap case, and similar trends are observed, even though no destabilizing effect of advection is observed within the range of ${\mathit{Re}}_{z} $ considered. Comparison with the experiment of Coney & Mobbs (Proc. Inst. Mech. Engrs, vol. 184 Pt 3L, 1969–70, pp. 10–17) for $\eta = 0. 89$ shows good agreement, despite small discrepancies attributed to finite length effects. [ABSTRACT FROM PUBLISHER]

The flow characteristics of Taylor–Couette–Poiseuille flow induced by supercritical carbon dioxide in an annular gap play a pivotal role in determining the overall performance of the rotating machinery. To accurately design the structural components of rotating machinery and enhance its efficiency, this study employs the large eddy simulation method to investigate the flow behavior of Taylor–Couette–Poiseuille flow with supercritical carbon dioxide within an annular gap. The results reveal that vortices are predominantly generated near the inner wall. Initially, the flow exhibits small swirl vortices, spiral ring vortices, and annular vortices along the flow direction. As the flow progresses, these small vortices at the inlet region transition into hairpin swirl vortices. Finally, turbulent flow disturbances lead to the fragmentation and merging of spiral and annular vortices, resulting in a flow field characterized by high-frequency hairpin swirl vortices and small vortices with strong randomness. An increase in the swirl number causes the initial position of the Taylor vortex to shift toward the inlet, while the turbulent kinetic energy is more active on the outer wall side than the inner wall side. Along the flow direction, the vortices experience a developmental process involving stabilization, diffusion, and mixing. Varying the radius ratio affects the magnitude of vorticity, reduces velocity fluctuations in a regular pattern, and alters the distribution of helicity bands from wide and sparse to compact and dense groupings. As the axial Reynolds number increases, the magnitude of vortices grows, leading to more severe velocity fluctuations and the transformation of the helicity bands from a regular annular pattern to fluctuating vortices bands, accompanied by a decrease in helicity. [ABSTRACT FROM AUTHOR]

We reconstruct a kinematically admissible (volume-preserving) three-dimensional velocity field corresponding to the stationary helical vortex (SHV) mode which is observed in the Taylor-Couette-Poiseuille (TCP) system with a ratio of inner to outer cylinder radii of 0.5 and a length to annulus gap ratio of 16, starting from experimental data obtained via magnetic resonance imaging (MRI) for Rey = 11.14 and Ta1/2 = 170 in water. The goal of the present work is to provide a complete kinematic representation of a strongly nonlinear duct flow that is of importance in the fields of mixing and segregation, as well as in the study of the kinematic structure of three-dimensional flows. By a judicious choice of a set of global basis functions that exploit the helical symmetry of SHV, an analytical approximation of the streamfunction is obtained despite the coarse MRI data and the non-uniform distribution of measurement error. This approximation is given in terms of a truncated series of smooth functions that converges weakly in L2, and the reconstruction method is directly applicable to three-dimensional incompressible flows that possess a continuous volume-preserving symmetry. The SHV flow structure consists of a pair of asymmetric counter-rotating helical cells in a double helix structure, foliated with invariant helically symmetric surfaces containing fibre-like fluid particle orbits wrapped around the inner cylinder. Imposing general topological constraints, juxtaposing SHV with neighbouring hydrodynamic modes such as the propagating Taylor vortex flow and direct numerical simulation help corroborate the validity of the reconstruction of the SHV flow field. The kinematically admissible flow field obeys the Navier-Stokes equations with 10% accuracy, which is consistent with experimental error, and has the same flow portrait as the numerically computed flow. Global analysis of the SHV mode indicates that it corresponds to a minimum in dissipation and mixing in comparison with a wide class of perturbed neighbouring modes; hence it is a candidate for the study of particle segregation. To our knowledge, the present study reports the first synthesis of a physically realizable complex open flow that can be represented by an integrable Hamiltonian system starting from point-wise experimental data and using solely kinematic constraints. [ABSTRACT FROM AUTHOR]

Recently, meshless methods have become popular in numerically solving partial differential equations and have been employed to solve equations governing fluid flows, heat transfer, and species transport. In the present study, a numerical solver is developed employing the meshless framework to efficiently compute the hydrodynamic stability of fluid flows in complex geometries. The developed method is tested on two cases of Taylor–Couette flows. The concentric case represents the parallel flow assumption incorporated in the Orr–Sommerfeld model and the eccentric Taylor–Couette flow incorporates a non-parallel base flow with separation bubbles. The method was validated against earlier works by Marcus ["Simulation of Taylor-Couette flow. Part 1. Numerical methods and comparison with experiment," J. Fluid Mech. 146, 45–64 (1984)], Oikawa et al. ["Stability of flow between eccentric rotating cylinders," J. Phys. Soc. Jpn. 58, 2355–2364 (1989)], Leclercq et al. ["Temporal stability of eccentric Taylor–Couette–Poiseuille flow," J. Fluid Mech. 733, 68–99 (2013)], and Mittal et al. ["A finite element formulation for global linear stability analysis of a nominally two-dimensional base flow," Numer. Methods Fluids 75, 295–312 (2014)]. The results for the two cases and the effectiveness of the method are discussed in detail. The method is then applied to Taylor–Couette flow in an elliptical enclosure and the stability of the flow is investigated. [ABSTRACT FROM AUTHOR]

Parkinson's disease (PD) is the second most common neurodegenerative disorder in human and loss-of-functions DJ-1 mutations are associated with a familial form of early onset PD. Functionally, DJ-1 (PARK7), a neuroprotective protein, is known to support mitochondria and protect cells from oxidative stress. Mechanisms and agents by which the level of DJ-1 could be increased in the CNS are poorly described. RNS60 is a bioactive aqueous solution created by exposing normal saline to Taylor-Couette-Poiseuille flow under high oxygen pressure. Recently we have described neuroprotective, immunomodulatory and promyelinogenic properties of RNS60. Here we delineate that RNS60 is also capable of increasing the level of DJ-1 in mouse MN9D neuronal cells and primary dopaminergic neurons, highlighting another new neuroprotective effect of RNS60. While investigating the mechanism we found the presence of cAMP response element (CRE) in DJ-1 gene promoter and stimulation of CREB activation in neuronal cells by RNS60. Accordingly, RNS60 treatment increased the recruitment of CREB to the DJ-1 gene promoter in neuronal cells. Interestingly, RNS60 treatment also induced the enrollment of CREB-binding protein (CBP), but not the other histone acetyl transferase p300, to the promoter of DJ-1 gene. Moreover, knockdown of CREB by siRNA led to the inhibition of RNS60-mediated DJ-1 upregulation, indicating an important role of CREB in DJ-1 upregulation by RNS60. Together, these results indicate that RNS60 upregulates DJ-1 in neuronal cells via CREB–CBP pathway. It may be of benefit for PD and other neurodegenerative disorders. [ABSTRACT FROM AUTHOR]

Background: Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that affects the motor neuromuscular system leading to complete paralysis and premature death. The multifactorial nature of ALS that involves both cell-autonomous and non-cell-autonomous processes contributes to the lack of effective therapies, usually targeted to a single pathogenic mechanism. RNS60, an experimental drug containing oxygenated nanobubbles generated by modified Taylor-Couette-Poiseuille flow with elevated oxygen pressure, has shown anti-inflammatory and neuroprotective properties in different experimental paradigms. Since RNS60 interferes with multiple cellular mechanisms known to be involved in ALS pathology, we evaluated its effect in in vitro and in vivo models of ALS.Methods: Co-cultures of primary microglia/spinal neurons exposed to LPS and astrocytes/spinal neurons from SOD1G93A mice were used to examine the effect of RNS60 or normal saline (NS) on the selective motor neuron degeneration. Transgenic SOD1G93A mice were treated with RNS60 or NS (300 μl/mouse intraperitoneally every other day) starting at the disease onset and examined for disease progression as well as pathological and biochemical alterations.Results: RNS60 protected motor neurons in in vitro paradigms and slowed the disease progression of C57BL/6-SOD1G93A mice through a significant protection of spinal motor neurons and neuromuscular junctions. This was mediated by the (i) activation of an antioxidant response and generation of an anti-inflammatory environment in the spinal cord; (ii) activation of the PI3K-Akt pro-survival pathway in the spinal cord and sciatic nerves; (iii) reduced demyelination of the sciatic nerves; and (iv) elevation of peripheral CD4+/Foxp3+ T regulatory cell numbers. RNS60 did not show the same effects in 129Sv-SOD1G93A mice, which are unable to activate a protective immune response.Conclusion: RNS60 demonstrated significant therapeutic efficacy in C57BL/6-SOD1G93A mice by virtue of its effects on multiple disease mechanisms in motor neurons, glial cells, and peripheral immune cells. These findings, together with the excellent clinical safety profile, make RNS60 a promising candidate for ALS therapy and support further studies to unravel its molecular mechanism of action. In addition, the differences in efficacy of RNS60 in SOD1G93A mice of different strains may be relevant for identifying potential markers to predict efficacy in clinical trials. [ABSTRACT FROM AUTHOR]

An increase in central nervous system (CNS) remyelination and a decrease in CNS inflammation are important steps to halt the progression of multiple sclerosis (MS). RNS60 is a bioactive aqueous solution generated by subjecting normal saline to Taylor–Couette–Poiseuille flow under elevated oxygen pressure. Recently we have demonstrated that RNS60 exhibits anti-inflammatory properties. Here, we describe promyelinating property of RNS60. RNS60, but not normal saline (NS), RNS10.3 (TCP-modified saline without excess oxygen) or PNS60 (saline containing excess oxygen without TCP modification), stimulated the expression of myelin-specific genes and proteins (myelin basic protein, MBP; myelin oligodendrocyte glycoprotein, MOG and proteolipid protein, PLP) in primary mouse oligodendroglia and mixed glial cells. While investigating the mechanisms, we found that RNS60 treatment induced the activation of cAMP response element binding protein (CREB) in oligodendrocytes, ultimately leading to the recruitment of CREB to the promoters of myelin-specific genes. Furthermore, activation of type 1A p110β/α, but not type 1B p110γ, phosphatidylinositol-3 (PI-3) kinase by RNS60 together with abrogation of RNS60-mediated activation of CREB and upregulation of myelin genes by LY294002 (a specific inhibitor of PI-3 kinase) suggest that RNS60 upregulates the activation of CREB and the expression of myelin-specific molecules in oligodendrocytes via activation of PI3 kinase. These results highlight a novel promyelinating property of RNS60, which may be of benefit for MS and other demyelinating disorders. [ABSTRACT FROM AUTHOR]

Permanent magnet coupling (PMC) generates a large amount of thermal energy due to the eddy current induced in the metal isolation cylinder, resulting in performance degradation. The magnetic-thermal-mechanical coupling analysis has an important impact on the design and operation of PMC devices. In this paper, the Maxwell equations are solved based on the separated variable method; the 3D eddy current loss and magnetic torque equations are proposed; and the electrical conductivity, the convective heat transfer coefficient, and the magnetic-thermal-mechanical properties of PMC are presented. The 3D analytical coupling model calculates the temperature field and presents an uneven distribution of temperature along the coolant flow direction, and it then obtains a more precise magnetic field and torque under various temperatures. Furthermore, the working conditions such as rotor speed, coolant flow rate, and applied load are taken into consideration in the 3D analytical model. The results show that the eddy current loss is proportional to the square of the speed. With an increase in the load, the eddy current decreases. However, with an increase in the coolant flow, more eddy current loss would be produced, but the generated heat would be taken away by the increased coolant flow, resulting in a decrease in the temperature. The 3D analytical coupling model results are in good agreement with the experimental data, which is helpful to the design and optimization of the PMC system. [ABSTRACT FROM AUTHOR]

The development of electric gerotor pumps is a complex multiphysical optimization problem. To develop optimal systems, accurate simulation models are required to increase digital reliability. An important challenge is the accurate prediction of the pump behavior for extreme temperatures in automotive applications from − 40 °C to 110 °C, where the viscosity of the fluid changes significantly. Therefore, simulation-based methods (numerical methods for calculating viscous friction) were developed and validated by measurements, including climatic chamber tests. The results show a strong correlation between simulated and measured performance characteristics, especially in terms of volumetric flow rate ( < 5 % ), pump torque and efficiency ( < 7 % ) at different temperature and viscosity conditions over a wide speed range (1000–5000 rpm) and different system pressures (0.5–5 bar). A novel method for simulating the cold start behavior of pumps (journal bearing approach for outer gear in pump housing) was introduced and validated by measurements. The methods presented significantly reduce the need for physical testing and accelerate the development process, as the pump behavior at each operating point can be accurately predicted before a hardware prototype is built. This improves the understanding of gerotor pump characteristics and provides insights to further improve the model-based development of electric oil pumps for the automotive industry. [ABSTRACT FROM AUTHOR]

Developing a new and effective therapeutic approach against multiple sclerosis (MS) is always an important area of research. RNS60 is a bioactive aqueous solution generated by subjecting normal saline to Taylor-Couette-Poiseuille flow under elevated oxygen pressure. Recently we have demonstrated that RNS60, administered through intraperitoneal injection, ameliorated clinical symptoms and disease progression of experimental allergic encephalomyelitis (EAE), an animal model of MS. Since the intravenous route is not preferred for treating a chronic condition, we tested if nebulization of RNS60 could attenuate the disease process of adoptively-transferred EAE in mice. Although we could not directly image RNS60 after nebulization, nebulized Alexa680 reached spleen, spinal cord and different parts of the brain. Nebulization of RNS60 starting from the acute phase attenuated clinical symptoms of relapsing-remitting EAE in female SJL/J mice. RNS60 nebulization also inhibited perivascular cuffing, maintained the integrity of blood-brain and blood-spinal cord barriers, suppressed inflammation, normalized the expression of myelin genes, and blocked demyelination in the CNS of EAE mice. On the immunomodulatory front, nebulization of RNS60 to EAE mice led to the enrichment of anti-autoimmune regulatory T cells (Tregs) and suppression of autoimmune Th17 cells. Together, these results suggest that nebulization of RNS60 may be used to control aberrant immune responses in MS and other autoimmune disorders. [ABSTRACT FROM AUTHOR]

A motor stator-gap-rotor model is established based on the numerical heat transfer theory by using the finite volume method. The flow evolution of high-pressure natural gas in the gap with a radius ratio of 0.971 is investigated. The results demonstrate that the flow patterns of high pressure natural gas in the motor gap can be categorized into turbulent, spiral Taylor-Couette, and turbulent Taylor-Couette flow. The flow ranges are determined based on the Ta/Re2. Then, the flow and heat transfer characteristics of the cooling medium in the gap under different flow regimes as well as the mechanism of locally enhanced heat transfer in the gap by the Taylor-Couette flow are explored. Finally, the mathematical expressions for the Nusselt number of motor gap are determined in terms of the Reynolds number, Taylor number, and Prandtl number by fitting using the Levenberg-Marquardt and global optimization methods. Using these expressions, the flow and heat transfer characteristics in the motor gap can be predicted. Overall, this study provides useful and novel insights on the design of cooling systems for high-speed motors. [ABSTRACT FROM AUTHOR]

The windage loss in rotor‐stator gap has an important effect on rotating machinery, especially with higher rotational speed and fluid density. However, the mechanism of axial flow on windage loss in open shaft‐type gap is hardly studied in most literature. To clarify it, the influences of axial Reynolds number Reu and rotational Reynolds number Reω on skin friction coefficient Cf are investigated, and flow characteristics are analyzed with different gap geometry, radius ratio η. First, the results reveal that the Cf remains constant when Reu is less than 2.8 × 104 and increases rapidly as Reu when Reu ≥ 2.8 × 104, which indicates that the effect of axial velocity u on Cf is negligible for low Reu. The positive relative deviation Δ suggests that the axial flow makes windage loss and Cf rise. Besides, a larger number of Taylor vortexes fill with gap when the effect of the centrifugal force is larger than that of the inertial force, but they gradually disappear as Reu. Subsequently, the Cf and Δ increase as η, highlighting that the effect of u on windage loss and Cf is more prominent for larger η. The fact that vorticity near walls is larger than that at the center of gap reveals that windage loss arises from the interaction between walls and fluid rather than the dissipation with fluid itself. Finally, the model of Cf in shaft‐type gap is proposed in different Reω ranges based on numerical results, and the maximum sum of squares error of 1.02 × 10−5 and minimal R2 of 0.969 satisfy the requirement of fitting accuracy and indicate that the fitting model can accurately predict Cf. The conclusions significantly help predict windage loss in open shaft‐type gap with axial flow, and further improve the design for generators of supercritical CO2 turbine‐alternator‐compressor unit. [ABSTRACT FROM AUTHOR]

Neuroinflammation underlies the pathogenesis of various neurodegenerative disorders including Parkinson's disease (PD). Despite intense investigations, no effective therapy is available to stop its onset or halt its progression. RNS60 is a novel therapeutic containing charge-stabilized nanobubbles in saline, generated by subjecting normal saline to Taylor-Couette-Poiseuille flow under elevated oxygen pressure. Recently, we have delineated that RNS60 inhibits the expression of proinflammatory molecules in glial cells via type 1A phosphatidylinositol-3 kinase (PI3K)-mediated upregulation of IκBα. In this study, we demonstrate that RNS60 inhibited the expression of proinflammatory molecules in cultured microglial cells stimulated by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridium ion (MPP) and in vivo in the nigra of MPTP-intoxicated mice. While investigating the underlying mechanisms, we found that MPTP intoxication rapidly stimulated the activation of type IB PI3K p110γ in the nigra, while suppressing the activation of type IA PI3K p110α/β. Interestingly, RNS60 treatment suppressed the activation of p110γ PI3K, while inducing the activation of p110α/β PI3K in the nigra of MPTP-intoxicated mice. Accordingly, RNS60 treatment increased the level of IκBα and inhibited the activation of NF-κB in the SNpc of MPTP-intoxicated mice. These findings paralleled dopaminergic neuronal protection, normalized striatal neurotransmitters, and improved motor functions in MPTP-intoxicated mice. These results strongly suggest a promising therapeutic role of this simple modified saline in PD and other neuroinflammatory disorders. [ABSTRACT FROM AUTHOR]

Abstract: Nanobubbles are gas-filled features that spontaneously form at the interface of hydrophobic surfaces and aqueous solutions. In this study, an atomic force microscope (AFM) was used to characterize the morphology of nanobubbles formed on hydrophobic polystyrene (PS) and octadecyltrichlorosilane (OTS) films immersed in DI water, saline, saline with oxygen and an electrokinetically altered saline solution produced with Taylor–Couette–Poiseuille flow under elevated oxygen pressure. AFM force spectroscopy was used to evaluate hydrodynamic and electrostatic forces and boundary slip condition in various fluids. The effect of solution, electric field and surface charge on shape, size and density of nanobubbles as well as slip length was quantified and the results and underlying mechanisms are presented in this paper. [Copyright &y& Elsevier]