Toroidal Channel Research Articles

Analysis of Intracranial Aneurysm Haemodynamics Altered by Wall Movement.

Computational fluid dynamics is intensively used to deepen our understanding of aneurysm growth and rupture in an attempt to support physicians during therapy planning. Numerous studies assumed fully rigid vessel walls in their simulations, whose sole haemodynamics may fail to provide a satisfactory criterion for rupture risk assessment. Moreover, direct in vivo observations of intracranial aneurysm pulsation were recently reported, encouraging the development of fluid-structure interaction for their modelling and for new assessments. In this work, we describe a new fluid-structure interaction functional setting for the careful evaluation of different aneurysm shapes. The configurations consist of three real aneurysm domes positioned on a toroidal channel. All geometric features, employed meshes, flow quantities, comparisons with the rigid wall model and corresponding plots are provided for the sake of reproducibility. The results emphasise the alteration of flow patterns and haemodynamic descriptors when wall deformations were taken into account compared with a standard rigid wall approach, thereby underlining the impact of fluid-structure interaction modelling.

Modification of the swirling well cell culture model to alter shear stress metrics.

Effects of hemodynamic shear stress on endothelial cells have been extensively investigated using the "swirling well" method, in which cells are cultured in dishes or multiwell plates placed on an orbital shaker. A wave rotates around the well, producing complex patterns of shear. The method allows chronic exposure to flow with high throughput at low cost but has two disadvantages: a number of shear stress characteristics change in a broadly similar way from the center to the edge of the well, and cells at one location in the well may release mediators into the medium that affect the behavior of cells at other locations, exposed to different shears. These properties make it challenging to correlate cell properties with shear. The present study investigated simple alterations to ameliorate these issues. Flows were obtained by numerical simulation. Increasing the volume of fluid in the well-altered dimensional but not dimensionless shear metrics. Adding a central cylinder to the base of the well-forced fluid to flow in a square toroidal channel and reduced multidirectionality. Conversely, suspending a cylinder above the base of the well made the flow highly multidirectional. Increasing viscosity in the latter model increased the magnitude of dimensional but not dimensionless metrics. Finally, tilting the well changed the patterns of different wall shear stressmetrics in different ways. Collectively, these methods allow similar flows over most of the cells cultured and/or allow the separation of different shear metrics. A combination of the methods overcomes the limitations of the baseline model.

Unsteady Turbulent Swirling Flows in a Thick Torus

Experimental study of unsteady swirling flows generated by special diverters in closed toroidal channels with different curvatures was carried out. The formation of a swirling flow in a toroidal channel is crucially different from the case of a straight cylindrical channel. It essentially depends on the curvature and is hindered by its increasing. The complex dynamics of swirling flow tightly connects with the interaction of jets after the diverter. Measurements of flow velocity using tracer’s tracks showed that the evolution of the toroidal component in torus with one diverter can be divided into two-time intervals with different power laws. The evolution of the poloidal component is rather characterized by one slope “-2/3”.

Solution to the Problem of Convective Heat Transfer in a Toroidal Channel Using a Curvilinear Coordinate System

Solution to the Problem of Convective Heat Transfer in a Toroidal Channel Using a Curvilinear Coordinate System

Non-Newtonian Fluid Flow Modeling in the Inertial Viscometer with a Computer Vision System

Purpose of research. Development of theoretical premises for the new inertial viscometer, as well as the development of an approximate model of the viscosity fluid flow using convolutional neural networks and laser speckle contrast imaging data.Methods. The study consists of two parts. The first is devoted to a theoretical study of viscosity fluid flow in the toroidal channel of еру new inertial viscometer. The mathematical model of the flow includes the dimensionless equations of Navier-Stokes and convective heat conduction, the analysis of which made it possible to estimate the conditions for the uniformity of pressure and temperature fields. The numerical solution of the simplified Navier-Stokes equation was obtained by the control volume method. The computational experiment made it possible to identify additional operating conditions for the viscometer. The second part of the research is aimed at solving the problem of predicting the values of the shear strain rate on the tour surface and the flow rate. The approximate flow model is based on an ensemble of convolutional neural networks trained on data from laser speckle-contrast visualization of a fluid flow in a transparent tube.Results. The recommendations on the operating parameters of the inertial viscometer for the studied types of liquids in a given viscosity range are obtained. An approximate model has been developed in the form of an ensemble of deep neural networks, which makes it possible to determine the volumetric flow rate and the shear strain rate on the flow surface based on fluid flow images.Conclusion. The approximate Navier-Stokes equation obtained as a result of theoretical analysis for the flow of a viscous fluid in a toroidal channel can be used to numerical determination the kinematic viscosity. So, the necessary flow characteristics, such as volumetric flow rate and shear strain rate on the flow surface, can be found using the developed and pretrained convolutional neural network based on laser speck contrast imaging data. The test fluid can be any non-Newtonian fluid capable of reflecting coherent radiation. In particular, it can be physiological fluids, including blood.

MHD grid-turbulence in a closed decaying flow of liquid sodium

Grid-induced turbulent flows of liquid sodium in a toroidal channel at high Reynolds numbers and moderate magnetic Reynolds numbers are studied experimentally. Grids with a pitch of 15 mm and 31 mm were used, and one or two grids were installed in the channel. It is shown that the dynamics of the pulsed turbulent flow in the channel with grids differs significantly from that observed in a free channel, where the turbulence develops on the scale of the channel cross-section. Measurements of the characteristics of velocity and magnetic field pulsations have shown that induction effects in the unsteady pulse flow have time to manifest themselves in full. The spectra of velocity and magnetic field pulsations are obtained.

Heterogeneous toroidal spiral particles for islet encapsulation.

Transplantable cell encapsulation systems present a promising approach to deliver a therapeutic solution from hormone-producing cells for the treatment of endocrine diseases like type 1 diabetes. However, the development of a broadly effective and safe transplantation system has been challenging. While some current micro-sized capsules have been optimized for adequate nutrient and metabolic transport, they lack the robustness and retrievability for the clinical safety translation that macro-devices may offer. An existing challenge to be addressed in the current macro-devices is their configuration which may lead to unsatisfactory mass transfer. Here, we design and characterize a millimeter-size particle system of poly-ethylene glycol (PEG) featuring internal toroidal spiral channels, called toroidal spiral particles (TSPs). The characteristic internal structure of the TSPs allows for large encapsulation capacity and large surface area available to all the encapsulated cell mass for effective molecular diffusion. The polymeric matrix renders the particle flexible yet robust for safe transplantation and retrieval. We demonstrate the feasibility of fabricating these particles with various polymer compositions, while optimizing their mechanical properties as well as glucose and insulin permeability. Encapsulation of islets of Langerhans is achieved with high loading capacity (∼160 IEQ per TSP) and excellent cell viability. TSP-encapsulated islets showed similar glucose-stimulated insulin secretion to the naked islets. Preliminary biocompatibility of the TSPs on naïve C57BL/6 mice shows minimal inflammatory response after 4-week transplantation into the intraperitoneal (IP) space. Long-term therapeutic efficacy of encapsulated islets needs to be confirmed in diabetic rodent models in the future, while determining minimal mass required to reverse diabetes. However, we believe from the in vitro favorable results and the TSPs' unique design that TSPs may provide a safe, effective method to transplant and retrieve therapeutic cells for type 1 diabetes treatment and may also be applicable for other cell therapies.

Electric Current Generation From Dendrimer-Based Magnetofluid Flow in a Toroidal Chamber

Nowadays, the sustainable power generation is the global movement to reduce the environmental impact of fossil fuel. In this framework, new materials are vital in enabling technologies that can offer promising solutions for a sustainable energy future. Magnetofluid (MFs) holds great promise for innovation to power generation. MFs are homogenous combinations of a base fluid and nanoparticles with permanent magnetic dipoles. In this article, the MF composed by polyglycerol dendrimer (PGlyD) as a base fluid for superparamagnetic iron oxide nanoparticles (SPIONs) was used to generate a time-varying magnetic flux and induce an electromotive force in a coil. The MF has been prepared from in situ electrosynthesis of 10–19 nm diameter SPIONs inside the cavities of PGlyD and characterized using X-ray diffraction (XRD), thermogravimetric analysis (TG/DTA), and transmission electron microscopy (TEM). The magnetization of the PGlyD-SPIONs underflow in a toroidal channel creates a time-varying magnetic flux and induces an electromagnetic force in a coil around the torus generating an electric current. The flow of the magnetized PGLyD-SPIONs in the toroidal chamber was able to give an output current of 0.3 mA. This development of power generators based on PGlyD-SPIONs will be promising for portable electronics.

Flow topology of rare back flow events and critical points in turbulent channels and toroidal pipes

A study of the back flow events and critical points in the flow through a toroidal pipe at friction Reynolds number Reτ ≈ 650 is performed and compared with the results in a turbulent channel flow at Reτ ≈ 934. The statistics and topological properties of the back flow events are analysed and discussed. Conditionally-averaged flow fields in the vicinity of the back flow event are obtained, and the results for the torus show a similar streamwise wall-shear stress topology which varies considerably for the spanwise wall-shear stress when compared to the channel flow. The comparison between the toroidal pipe and channel flows also shows fewer back flow events and critical points in the torus. This cannot be solely attributed to differences in Reynolds number, but is a clear effect of the secondary flow present in the toroidal pipe. A possible mechanism is the effect of the secondary flow present in the torus, which convects momentum from the inner to the outer bend through the core of the pipe, and back from the outer to the inner bend through the pipe walls. In the region around the critical points, the skin-friction streamlines and vorticity lines exhibit similar flow characteristics with a node and saddle pair for both flows. These results indicate that back flow events and critical points are genuine features of wall-bounded turbulence, and are not artifacts of specific boundary or inflow conditions in simulations and/or measurement uncertainties in experiments.

Transition from turbulent to coherent flows in confined three-dimensional active fluids.

Transport of fluid through a pipe is essential for the operation of macroscale machines and microfluidic devices. Conventional fluids only flow in response to external pressure. We demonstrate that an active isotropic fluid, composed of microtubules and molecular motors, autonomously flows through meter-long three-dimensional channels. We establish control over the magnitude, velocity profile, and direction of the self-organized flows and correlate these to the structure of the extensile microtubule bundles. The inherently three-dimensional transition from bulk-turbulent to confined-coherent flows occurs concomitantly with a transition in the bundle orientational order near the surface and is controlled by a scale-invariant criterion related to the channel profile. The nonequilibrium transition of confined isotropic active fluids can be used to engineer self-organized soft machines.

Self-localized and self-constricted electromagnetic field in plasma and atmosphere

A possibility of creation of a super-high-frequency electromagnetic-field clot in the plasma is shown. Two cases of the field self-localization in the plasma are considered. In the first case, a super-high-frequency electric field creates an annular channel by displacing the plasma and induces a curl-like magnetic field inside. In the second case, the electric field creates a toroidal channel where different field structures are possible. For example, the magnetic lines of the force are aligned along the big circle of the torus, while the curl-like electric lines are aligned along the small circle. Otherwise, the magnetic field is curl-like and the electric-field lines are aligned along the big circle. We evaluate the electric field energy that is required for a curl-like structure of about 3 cm in size to exist during 10 s in the atmospheric air. This energy sustains plasma in the vicinity of the curl-like area.

Direct numerical simulation of electromagnetically forced flows using OpenFOAM

We present direct numerical simulation results of a conducting fluid subject to the Lorentz force resulting from an external static magnetic field normal to the electric current direction. This research discipline, generally known as electromagnetic forcing flows, is motivated by many engineering and physical applications such as plasma physics, geophysics, weather prediction and solid melting processes. In this paper, a computational fluid dynamics (CFD) code is developed using the open source C++ library OpenFOAM. The solver is based on the electric potential method coupled to the Navier–Stokes equations. The code is then benchmarked to other well-known solvers using different numerical techniques and to the experiment. Excellent agreement is obtained for the forced toroidal channel flow, with three-dimensional dynamics, as well as for the confined vortex-pair in a cylindrical container, with quasi-two-dimensional dynamics. Quasi-two-dimensional forced flow in the presence of non-uniform magnetic field at low Hartmann number is also used for comparison. Furthermore, qualitative comparison with the experiment is made where we are able to successfully simulate the vortex pairs generated by the Lorentz force and the effect of the magnetic field gradient leading to the so-called gradB jets in accordance with the experiment.

Nonstationary magnetic microstructures in stellar thin accretion disks

We examine the morphology of magnetic structures in thin plasma accretion disks, generalizing a stationary ideal magnetohydrodynamics model for the time-dependent viscoresistive case. Our analysis deals with small-scale perturbations to a central dipolelike magnetic field, which give rise-as in the ideal case-to the periodic modulation of magnetic flux surfaces along the radial direction, corresponding to the formation of a toroidal current channel's sequence. These microstructures suffer an exponential damping in time because of the nonzero resistivity coefficient, allowing us to define a configuration lifetime which mainly depends on the midplane temperature and on the length scale of the structure itself. By means of this lifetime, we show that the microstructures can exist within the inner regions of stellar disks in a defined range of temperatures, precisely for radii of R</~10(9)cm and temperatures of 10(4)K</~T</~10(5)K. Their duration-minutes to hours-is shown to be consistent with local transient phenomena rather than with a steady equilibrium.

Magnetic field advection in liquid sodium flow in toroidal channel

Magnetic field advection in liquid sodium flow in toroidal channel

Enhanced control of light and sound trajectories with three-dimensional gradient index lenses

We numerically study the focusing and bending effects of light and sound waves through heterogeneous isotropic cylindrical and spherical devices. We first point out that transformation optics and acoustics show that the control of light requires spatially varying anisotropic permittivity and permeability, while the control of sound is achieved via spatially anisotropic density and isotropic compressibility. Moreover, homogenization theory applied to electromagnetic and acoustic periodic structures leads to such artificial (although not spatially varying) anisotropic permittivity, permeability and density. We stress that homogenization is thus a natural mathematical tool for the design of structured metamaterials. To illustrate the two-step geometric transform-homogenization approach, we consider the design of cylindrical and spherical electromagnetic and acoustic lenses displaying some artificial anisotropy along their optical axis (direction of periodicity of the structural elements). Applications are sought in the design of Eaton and Luneburg lenses bending light at angles ranging from 90° to 360°, or mimicking a Schwartzchild metric, i.e. a black hole. All of these spherical metamaterials are characterized by a refractive index varying inversely with the radius which is approximated by concentric layers of homogeneous material. We finally propose some structured cylindrical metamaterials consisting of infinitely conducting or rigid toroidal channels in a homogeneous bulk material focusing light or sound waves. The functionality of these metamaterials is demonstrated via full-wave three-dimensional computations using nodal elements in the context of acoustics, and finite edge-elements in electromagnetics.

Turbulent viscosity and turbulent magnetic diffusivity in a decaying spin-down flow of liquid sodium

The free decay of a strong flow of liquid sodium (at Reynolds number defined via the maximal mean velocity and the radius of the channel cross section up to Re≈3×10(60) and the corresponding magnetic Reynolds number up to Rm≈30) generated by the sudden stop of a rapidly rotating toroidal channel is studied experimentally. The toroidal and poloidal components of velocity are measured using a potential probe. We describe the onset of motion, the evolution of strongly anisotropic fluctuations, and the homogenization and decay of turbulence in the final period. We analyze the statistical characteristics of velocity fields in relation to the behavior of effective magnetic diffusivity estimated from measurements of the phase shift between the induced and applied magnetic fields. For the late (self-similar) decay of turbulent flow, turbulent viscosity is shown to be dependent on the root-mean-square velocity pulsations and can be expressed as νt∼νRe1.3. The behavior of turbulent magnetic diffusivity depends on the magnetic Reynolds number defined in terms of the root-mean-square velocity pulsations. At low magnetic Reynolds numbers (Rmrms<1), turbulent magnetic diffusivity grows rapidly with increasing velocity pulsations (ηt∼ηRmrms2). If the magnetic Reynolds number exceeds unity, the behavior of turbulent magnetic diffusivity becomes similar to the behavior of turbulent viscosity. The highest values of turbulent magnetic diffusivity are achieved at the end of braking, which corresponds to the transient stage of a strongly anisotropic turbulent flow in which the poloidal velocity oscillations prevail.

Focussing light through a stack of toroidal channels in PMMA

We propose a transformational design of an axi-symmetric gradient lens for electromagnetic waves. We show that a metamaterial consisting of toroidal air channels of diameters ranging from 23 nm to 190 nm in a matrix of Polymethylmethacrylate (PMMA) allows for a focussing effect of light over a large bandwidth i.e. [600-1000] nm. We finally propose a simplified design of lens allowing for a two-photon lithography implementation.

The screw dynamo in a thick torus

AbstractThe problem of magnetic field generation under screw motion in a toroidal channel is studied numerically. The screw dynamo in the cylinder with periodical boundary conditions was found to be a suitable approximation for generation of the magnetic field by a screw flow in a thin torus. For the thick torus, a principally new solution of the screw dynamo problem was obtained. In this case the growing global magnetic field mode has the scale of a maximal geometrical size of the torus and does not vanish on the axis of the torus (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Direct Measurement of Effective Magnetic Diffusivity in Turbulent Flow of Liquid Sodium

The first direct measurements of effective magnetic diffusivity in turbulent flow of electroconductive fluids (the so-called β effect) under the magnetic Reynolds number Rm≫1 are reported. The measurements are performed in a nonstationary turbulent flow of liquid sodium, generated in a closed toroidal channel. The peak level of the Reynolds number reached Re≈3×10(6), which corresponds to the magnetic Reynolds number Rm≈30. The magnetic diffusivity of the liquid metal was determined by measuring the phase shift between the induced and the applied magnetic fields. The maximal deviation of magnetic diffusivity from its laminar value reaches about 50%.

An integrated charge exchange recombination spectroscopy/beam emission spectroscopy diagnostic for Alcator C-Mod tokamak

A novel integrated charge exchange recombination spectroscopy (CXRS)/beam emission spectroscopy (BES) system is proposed for C-Mod, in which both measurements are taken from a shared viewing geometry. The supplementary BES system serves to quantify local beam densities and supplants the common calculation of beam attenuation. The new system employs two optical viewing arrays, 20 poloidal and 22 toroidal channels. A dichroic filter splits the light between two spectrometers operating at different wavelengths for impurity ion and beam neutrals emission. In this arrangement, the impurity density is inferred from the electron density, measured BES and CXRS spectral radiances, and atomic emission rates.