Symmetric Velocity Profiles Research Articles

Fluid dynamics, structural, micro-structural, and kinematic analyses on the Kuh-e-Namak (Dashti) salt diapiric rectangular cuboid channel flow, Iran

A study was conducted to investigate the Kuh-e-Namak (Dashti) salt diapir using fluid dynamics, structural, and microstructural, analyses. The study focused on transient flow caused by salt diapirism within the restraining bend of the Kazerun fault system. The salt diapir is located in Bushehr Province, Iran, and it was found that it represents Newtonian viscous flow within a rectangular cuboid channel, rather than a circular channel as previously thought. The study discovered that the salt diapir underwent laminar irrotational flow (Re = 1147.31) upward, with the symmetric parabola velocity profile dominated by Poiseuille flow. When loaded by sedimentary overburden, the salt tended to migrate. The upper part of the salt dome and diapiric flow transferred from irrotational laminar Poiseuille flow to transient Poiseuille-Couette and turbulent Poiseuille-Couette flows with a non-uniform asymmetric parabola profile. The drag sheath folds from diapiric flow showed monoclinic symmetry patterns, which led to a relative increase in the ellipticity of individual sheath fold rings to define the analogous eye-folds and cat ‘s-eye-folds. The presence of porphyroclasts or vortexes of σ, δ, and φ types in sheath folds indicates that the upper sections of the salt dome and diapir went through a Poiseuille-Couette flow or transient and turbulent flow during a later stage. The salt transient and turbulent flow can gradually lead to increased shear stress and high strain rates that are superposed by sub-simple shear, resulting in activation of the faults and consequently, the earthquake as we have seen in the destructive Kaki-Shonbe earthquake (Mw = 6.3).

Modeling trajectories of human speech articulators using general Tau theory

This paper presents an application of general Tau theory to the modeling and analysis of articulatory trajectories in speech. We evaluated the model using electromagnetic articulometry data from 12 native speakers of English reading a common text, where trajectories of the following sensors were fitted: lower and upper lips, jaw, and three tongue sensors. Additionally, we analyzed trajectories of the lip aperture signal. Our experiments show that the general Tau theory model gives a better fit than existing (i) methods based on critically damped oscillators, and (ii) a method based on sequential target approximation. These findings support the hypothesis of Tau-guided movements of articulators during speech production. In the second part of the paper, our Tau theory analysis shows that articulatory movements follow similar velocity profile distributions across speakers. In particular, the value of the shape parameter κ of the Tau theory equation is identically distributed across speakers, following a unimodal distribution. The statistical mode of the distribution corresponds to the value of κ that generates a symmetric velocity profile. The analysis of the statistical distribution of κ values also reveals that its variance decreases when greater articulatory effort is required, such that produced articulatory effort remains close to that predicted by the theoretical minimal cost function based on forces acting on the moving articulator. This provides new evidence that articulatory effort is optimized during speech production.

Numerical analysis of liquid flow measurement using multipath ultrasonic phased array flowmeter

In this paper, multipath ultrasonic flowmeter using phased array transducer is introduced to measure the flowrate. In the proposed flowmeter, the path velocities are achieved by dynamic beam steering via phased array sensor then numerical integration is used to calculate the flowrate. Turbulent flow profile through a straight pipe, flow field downstream of single bend, and double bend are studied in this paper. For each case, the influence of the number of paths, beam angle, and installation angle on the performance of the proposed flowmeter is discussed. Because of symmetric velocity profile for turbulent flow through the straight pipe, relative errors are not dependent on the installation angle and its minimum value is obtained 0.03 % under [±56.6°, 0] path arrangement. Relative errors after single and double bend depend on the installation angle due to the asymmetric flow field. In 3-path configuration, for velocity profile after single bend and double bend, the minimum error range is 1.35 % and 2.38 % under [±55o, 0] and [±45o, 0] path arrangement, respectively. In 5-path arrangement, after single bend and double bend, the minimum error range is achieved by 0.14 % and 1.03 % under [±70o, ±35o, 0] and [±65o, ±25o, 0], respectively. The validity of multipath ultrasonic phased array flowmeter after the single bend in Re = 2 × 105 to 106 has been examined with the computational fluid dynamics simulation. The maximum absolute relative error under [±55o,0] and [±70o,±35o,0] was achieved at about 3 % and 1.8 % respectively.

JMEMS Letters Fabrication of Self-Sealed Circular Microfluidic Channels in Glass by Thermal Blowing Method

We report fabrication of circular glass microchannels with radius less than 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> using the glass blowing technique. Silicon trenches filled with nitrogen are used for microchannel fabrication. We report an interesting reflow regime where the flowing glass fills the silicon trenches to form a completely circular microchannel. Circular microchannels have symmetric velocity profile and do not suffer from flow stagnation problems observed in rectangular channels. Besides circular shape, fabrication conditions of the semi-circular and elliptically shaped channels are also discussed. A mathematical model explaining the observation is also presented and is compared with the experimental results. [2021-0183]

Group-velocity symmetry in photonic crystal fibre for ultra-tunable quantum frequency conversion

Low-noise frequency conversion of single photons is a critical tool in establishing fibre-based quantum networks. We show that a single photonic crystal fibre can achieve frequency conversion by Bragg-scattering four-wave mixing of source photons from an ultra-broad wavelength range by engineering a symmetric group velocity profile. Furthermore, we discuss how pump tuning can mitigate realistic discrepancies in device fabrication. This enables a single highly adaptable frequency conversion interface to link disparate nodes in a quantum network via the telecoms band.

Effects of inflow boundary layer on the wake of a radially non-uniform porous disk

This study presents the results of an experimental investigation focusing on the effects of the inflow boundary layer on the wake characteristics of a 0.12 m diameter porous disk with radially non-uniform porosity in terms of mean flow, turbulence, and wake scaling. Two-dimensional two-component particle image velocimetry measurements within the wake are performed up to 7.5 diameters downstream as the disk is lowered deeper into a boundary layer that is representative of a neutral atmospheric boundary layer over a flat terrain. Results show that otherwise symmetrical wake velocity profiles that exist outside the boundary layer get skewed and sheared around the disk centerline in the boundary layer due to the inflow wind shear. The turbulent kinetic energy, its production, and Reynolds shear stress levels in the wake get asymmetrical around the centerline of the disk such that the production of turbulent kinetic energy is observed to be higher above centerline. Due to the inflow shear, the wake centerline gets shifted downwards (i.e., toward the wind tunnel wall), which is in contrast to the observations on real wind turbine wakes in the literature where the wake actually lifts up. The asymmetrical and skewed velocity profiles both in the streamwise and cross-stream directions can be collapsed onto a single function by using proper wake scaling parameters based on the ratio of local strain to average strain within the velocity profile calculated separately for either side of the wake.

Poloidally resolved measurements of the perpendicular propagation velocity of density fluctuations in ASDEX Upgrade L-mode plasmas

Poloidal asymmetries of the propagation velocity of density fluctuations perpendicular to the magnetic field measured with Doppler reflectometry have been reported in several magnetic confinement plasma devices. Careful analysis of a large variety of different low confinement mode plasma scenarios performed at the ASDEX Upgrade tokamak does not reveal such an asymmetry outside the uncertainties of the evaluation process of the measurement data. The perpendicular velocity is investigated between mid-radius and the plasma edge and follows the poloidal dependence of the E × B drift velocity regardless of the probed turbulence structure size. Compared to measurements of a charge exchange recombination spectroscopy diagnostic this points towards a significantly smaller phase velocity than the E × B drift velocity. The analysis technique is presented in a representative discharge together with a sensitivity study of the impact of density, magneto hydrodynamic equilibrium and diagnostic alignment on the interpretation of the measured Doppler shift using ray tracing and thus on poloidal asymmetries. Three more highly different plasma scenarios with poloidally symmetric velocity profiles are shown.

Mechanically driven circulation in a rotating cylinder/disk device

The circulation flow of a viscous incompressible fluid in the cylindrical containers bounded by the ends with the rotating and fixed disks are explored. The main goal of the research is aimed to study influence of rotation of casing and end disk on a circulation flow in a cylinder/disk device. This problem relates to inducing a circulation flow in a mechanical centrifuge for mixture separation. To solve this complex problem, an approximate calculation approach is proposed. It is based both on the integral relationships reducing to the balance of the azimuthal moment friction forces acting on the rotating volume and continuity of a circulation flow. To evaluate the friction forces at the ends of a cylinder, the case of infinitely extended disks is considered. For this case, the approximate analytical solutions of the hydrodynamic problem for the turbulent boundary layers on the rotating and fixed extended disks are obtained. In contrast to the previously published works, the inertial convective term associated with the angular momentum transfer from the external flow to the boundary layer in the equations of motion and the symmetrical radial velocity profile are taken into account.

Transient freezing of water between two parallel plates: A combined experimental and modelling study

The transient freezing/solidification of water subjected to shear flow inside a rectangular cell is investigated under laminar flow conditions. A flow of freezing water is established inside the cell by cooling the top surface of the conductive, copper plate that forms the cell’s top side by contact with boiling liquid nitrogen (−197∘C). This heat removal results in an ice layer that forms and grows gradually on the ceiling of the cell, which is subjected to shear from the flow below it inside the channel. The spatiotemporal characteristics of the ice layer are recorded with optical, laser-based measurements and are compared with predictions from a transient freezing model that is developed for this purpose. Furthermore, tracer particles are introduced into the flow to aid the tracking of the ice layer and to allow for measurements based on particle image velocimetry (PIV) of the velocity field inside the flow during the ice-layer evolution. After an initial time-lag/‘buffer’ period (of 5−40 s) that depends on the flow conditions, a quasi-linear growth of the ice layer is observed; at longer times the thickness of the ice layer reaches a maximum and then decreases again. The increase in the thickness, and hence thermal resistance, of the ice layer is counter-balanced by a decrease in the temperature of the copper plate and, therefore, a decrease in the temperature difference across the ice layer. Furthermore, it is found that the flow is associated with symmetric velocity profiles, recorded along the vertical spanwise length between the ice layer at the top of the cell and the floor of the cell, while an increase of the velocity maxima is recorded as the ice layer gradually thickens and, consequently, the flow cross-section is reduced. A constant heat flux of 19.7 × 103 W m−2 is measured on the top side of the channel, while the heat transfer coefficient on the top side of the channel is found to be in the range of 90–110 W m−2 K−1, depending on the wall temperature. Finally, from comparisons against the experimental data, it is concluded that the model developed herein is able to predict the freezing of water and the growth of the ice layer in these flows over a range of water inlet temperatures and Reynolds numbers. This model can be incorporated in thermohydraulic codes for the design of relevant heat-exchange components in the precence of freezing/solidification.

Spatiotemporal Parameterization of Human Reaching Movements Based on Time Base Generator

Human reaching movement is characterized by the invariant features of linearity and the symmetrical bell-shaped velocity profile of the hand trajectory. Reaching movement has been widely evaluated in fields such as rehabilitation and interface design; however, no standardized protocols exist for data collection, processing, or analysis. This paper proposes a spatiotemporal parameterization method that evaluates reaching movements with a trajectory generation model based on a time base generator. The proposed method extracts motion information as a set of model parameters, such as motion duration, distance, and asymmetry of the bell-shaped velocity profile from the reaching data, that are estimated by fitting the model to reaching data with a robust parameter estimation method. The reaching trajectory generation model, for which a straight trajectory in a three-dimensional space is assumed, is also derived from the proposed model. Experiments were conducted using simulated data and real-world three-dimensional and one-dimensional human reaching movement datasets. The results show that the model assuming a straight trajectory in the three-dimensional space is reasonable for evaluating reaching movements. In addition, the model parameters were estimated with relatively greater robustness than were those of the conventional model and were highly correlated with physical features extracted from measured datasets. The results also showed that the parameters representing the asymmetry of the bell-shaped velocity profile differed between individuals. Therefore, the characteristics of reaching movements can be parameterized and evaluated with the proposed method.

Effect of carrier fluid rheology on shear-induced particle migration in asymmetric T-shaped bifurcation channel

Separation of particles from the carrier fluid of suspension is important in many engineering applications. In this work numerical simulations of particle migration during the flow of concentrated suspension through 3D asymmetric T-shaped bifurcating channels were carried out. The carrier fluids were considered to be non-Newtonian and inelastic. Diffusive flux model of shear-induced migration in conjugation with the power-law and Bird-Carreau constitutive models for the carrier fluid was used in the simulations. The velocity and particle concentration profiles in a non-Newtonian suspending fluid showed marked differences compared to that in the Newtonian carrier. Enhanced migration was observed in the case of shear thinning fluid while low for shear thickening. The symmetric velocity and concentration profiles in the inlet branch become asymmetric in the daughter branches and the degree of asymmetry strongly depends on the carrier fluid rheology. The results showed that the particle partitioning between daughter branches do not follow the fluid partitioning and the degree of separation depends on the relative volumetric flow rate of bulk suspension in the daughter branches. Higher separation efficiency was achieved for suspension in shear thinning fluid and relatively lower in Newtonian and shear thickening fluids.

Experimental investigation of particle migration in suspension flow through bifurcating microchannels

Experimental measurements of velocity and concentration profiles were carried out to study transport of non‐colloidal suspension in bifurcating micro channels for both diverging and converging flow conditions using a combination of mirco‐particle image velocimetry and particle tracking velocimetry techniques. Migration of particles across the streamline was observed and symmetric velocity and concentration profile in the inlet branch becomes asymmetric in the daughter branches. Further migration of particles toward the center of the channel in the outlet branch make the profiles again symmetric. The evolution of velocity and concentration profiles was observed to be different in the symmetric and asymmetric bifurcation channels. The comparison of the streamlines for the fluid and the particles showed significant deviation near the bifurcation region. This may explain why there is unequal flow and particle partitioning during flow of suspension in asymmetric bifurcating channels as reported in many previous studies. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2293–2307, 2018

Wall shear stress and velocity distributions in different types of stenotic bifurcations

Blood flow following Carreau-Yasuda viscosity model at steady-state through various categories of stenotic arterial bifurcations based on Movahed [1] was investigated by using finite element method. Reynolds number was fixed at 233. Results are reported in terms of Wall shear stress (WSS) and velocity distributions. The maximum peaks of WSS were found at the minimum flow area, where high velocities were present. Symmetric stenotic sites give rather symmetric WSS distribution and symmetric velocity profile, whereas on asymmetric sites, the skewness depends upon the presence of the stenotic site as it introduces curvature. Volumetric flow rate ratios at various locations were introduced to indicate the crucial conditions. In addition, levels of stenosis between 30-60 % based on flow area were considered. The 60 % level gave significantly higher WSS peak and the lowest WSS at the location behind the stenosis for the symmetric case. For the asymmetric case, the 50 and 60 % levels show the lowest WSS values at the end of the stenotic site.

Modeling Rossby Wave Breaking in the Southern Spring Stratosphere

Abstract Rossby wave breaking (RWB) plays a central role in the evolution of stratospheric flows. The generation and evolution of RWB is examined in the simple dynamical framework of a one-layer shallow-water system on a sphere. The initial condition represents a realistic, zonally symmetric velocity profile corresponding to the springtime southern stratosphere. Single zonal wavenumber Rossby waves, which are either stationary or traveling zonally with realistic speeds, are superimposed on the initial velocity profile. Particular attention is placed on the Lagrangian structures associated with RWB. The Lagrangian analysis is based on the calculation of trajectories and the application of a diagnostic tool known as the “M” function. Hyperbolic trajectories (HTs), produced by the transverse intersections of stable and unstable invariant manifolds, may yield chaotic saddles in M. Previous studies associated HTs with “cat’s eyes” generated by planetary wave breaking at the critical levels. HTs, and hence RWB, are found both outside and inside the stratospheric polar vortex (SPV). Significant findings are as follows: (i) stationary forcing produces HTs only outside of the SPV and (ii) eastward-traveling wave forcing can produce HTs both outside and inside of the SPV. In either case, HTs appear at or near the critical latitudes. RWB was found to occur inside the SPV even when the forcing was located completely outside. In all cases, the westerly jet remained impermeable throughout the simulations. The results suggest that the HT inside the SPV observed by de la Cámara et al. during the southern spring 2005 was due to RWB of an eastward-traveling wave of wavenumber 1.

The flow downstream of a bifurcation of a flow channel for uniform flow distribution via cascade flow channel bifurcations

Uniform flow distribution is an important and fundamental issue to miscellaneous devices. The present work studied the details of flow in a channel with a fundamental structure—a symmetric bifurcation of one flow channel into two sub-channels. The structure is designated to split one flow into two streams of even flow rate. Key geometric design factors of the flow channel are investigated regarding the effect to the development of a symmetric velocity profile after the flow channel bifurcation, as the symmetric velocity profile is critical to the even split of the flow into two streams in the next stage of flow channel bifurcation. The study is based on both two-dimensional and three-dimensional CFD analyses. Both laminar and turbulent flows are investigated. Commercial CFD software ANSYS FLUENT® was used. The numerical treatment of convection terms in governing equations was based on the QUICK scheme, and the SIMPLE algorithm was used to treat the coupling of pressure and velocity fields. The obtained results are of great significance to the design of flow distributors using cascade flow channel bifurcations.

Visuomotor adaptation to a visual rotation is gravity dependent.

Humans perform vertical and horizontal arm motions with different temporal patterns. The specific velocity profiles are chosen by the central nervous system by integrating the gravitational force field to minimize energy expenditure. However, what happens when a visuomotor rotation is applied, so that a motion performed in the horizontal plane is perceived as vertical? We investigated the dynamic of the adaptation of the spatial and temporal properties of a pointing motion during prolonged exposure to a 90° visuomotor rotation, where a horizontal movement was associated with a vertical visual feedback. We found that participants immediately adapted the spatial parameters of motion to the conflicting visual scene in order to keep their arm trajectory straight. In contrast, the initial symmetric velocity profiles specific for a horizontal motion were progressively modified during the conflict exposure, becoming more asymmetric and similar to those appropriate for a vertical motion. Importantly, this visual effect that increased with repetitions was not followed by a consistent aftereffect when the conflicting visual feedback was absent (catch and washout trials). In a control experiment we demonstrated that an intrinsic representation of the temporal structure of perceived vertical motions could provide the error signal allowing for this progressive adaptation of motion timing. These findings suggest that gravity strongly constrains motor learning and the reweighting process between visual and proprioceptive sensory inputs, leading to the selection of a motor plan that is suboptimal in terms of energy expenditure.

Turbulent slurry flow measurement using ultrasonic Doppler method in rectangular pipe

Distribution of velocity and Reynolds stress was measured using ultrasonic velocimetry in flows of water and Newtonian water-ballotini slurries in a pressurized Plexiglas pipe. Profiles of the measured parameters were sensed in the vertical plane at the centreline of a rectangular cross section of the pipe. Reference measurements in clear water produced expected symmetrical velocity profiles the shape of which was affected by secondary currents developed in the rectangular pipe. Slurry-flow experiments provided information on an effect of the concentration of solid grains on the internal structure of the flow. Strong attenuation of velocity fluctuations caused by a presence of grains was identified. The attenuation increased with the increasing local concentration of the grains.

Multiple solution for a nematic liquid crystal flowing in converging and divergent channels

We consider a nematic liquid crystal flowing in converging and divergent channels delimited by two intersecting solid planes forming angular sector region. There is a source or sink of nematic, at the planes intersection, whether the nematic flow is outwards or inwards. We find the planar multiple configurations of the director of the nematic satisfying in-plane planar hard-anchoring boundary conditions for 4′-n-pentyl-4-cyanobiphenyl (5CB). Also, we obtain the corresponding velocity profiles parametrised by the Reynolds number for non-slip boundary conditions. We have obtained both symmetric and asymmetric velocity profiles for outwards and inwards flows, nevertheless, none of these profiles has counterflows regions as it occurs for isotropic liquids. Finally, we calculate the mass rate and Frank’s elastic energy for the same multiple velocity profiles and nematic textures we found. We hope this model can be useful as an extreme confining case which helps to understand the industrially important processes of blade coating and cavity filling of liquid crystalline materials.

Shear flow of dense granular materials near smooth walls. I. Shear localization and constitutive laws in the boundary region

We report on a numerical study of the shear flow of a simple two-dimensional model of a granular material under controlled normal stress between two parallel smooth frictional walls moving with opposite velocities ± V. Discrete simulations, which are carried out with the contact dynamics method in dense assemblies of disks, reveal that, unlike rough walls made of strands of particles, smooth ones can lead to shear strain localization in the boundary layer. Specifically, we observe, for decreasing V, first a fluidlike regime (A), in which the whole granular layer is sheared, with a homogeneous strain rate except near the walls, then (B) a symmetric velocity profile with a solid block in the middle and strain localized near the walls, and finally (C) a state with broken symmetry in which the shear rate is confined to one boundary layer, while the bulk of the material moves together with the opposite wall. Both transitions are independent of system size and occur for specific values of V. Transient times are discussed. We show that the first transition, between regimes A and B, can be deduced from constitutive laws identified for the bulk material and the boundary layer, while the second one could be associated with an instability in the behavior of the boundary layer. The boundary zone constitutive law, however, is observed to depend on the state of the bulk material nearby.

Moving boundary simulation of airflow and micro-particle deposition in the human extra-thoracic airway under steady inspiration. Part I: Airflow

Airflow into the lung is the result of negative alveolar pressure caused by the simultaneous action of diaphragm contraction and rib cage expansion. However, all of the determinate CFD simulations on airflow and particle deposition in the human upper respiratory tract to date have employed a fixed boundary condition, i.e. uniform or axial symmetrical velocity profiles at the mouth inlet and outlet/opening boundary at the end of the airway. In this study, the realistic breathing mechanism, i.e. expansion of the pleural cavity, is mimicked by the fluid–structure interaction employing a junction box routine to assign the motion of the moving wall boundary at the bottom of the extra-thoracic airway model with an extra bell-mouthed tube. The airflow and particle deposition are investigated, particularly for the movable boundary cases, and compared with the fixed cases. In Part I, the flow characteristics which are important factors for particle deposition, i.e. pressure drop, turbulence intensity, secondary intensity and velocity profiles, are illustrated at three flow rates, as well as the detailed recirculation flow in the trachea region. Compared with the fixed boundary cases, several notable differences are found:(i) the velocity profiles at the mouth inlet are not uniform or axially symmetric, but askew with high-speed flow shifted to the upper wall of the mouth inlet tube, and a more evident recirculation zone occurs near the lower wall of the inlet tube; (ii) the pressure drop and turbulence intensity are lower and the secondary intensity is higher than that in the fixed boundary case because of the askew profile in the mouth cavity and modified recirculation flow in the trachea region; (iii) at three flow rates, the secondary intensities exhibit identical characteristics before the larynx where the turbulence fluctuations are very weak, but discrepancies are evident in the trachea region because of the high level of turbulence intensity and different pattern of recirculation zones; (iv) the length of the recirculation zones increase at three flow rates and the minor separation and reattachment occur in the middle portion of the recirculation flow, while the recirculation flow layer is divided into two parts at higher flow rates; (v) the peaks of the secondary flow intensity in the trachea region are located near the flow separation and reattachment points (both the major and minor) and the peaks of turbulence intensity in the trachea seem to correspond to the major separation and reattachment region.