Streamline Patterns Research Articles

Numerical investigation on the flow field of a modified vortex spinning system for producing core-spun yarns

A modified vortex spinning technology, which produces core-spun yarns by means of a tangentially injected swirling airflow, is of great prospect in view of its production rate and yarn structure. In this paper, a numerical study based on computational fluid dynamics is presented to investigate the characteristics of the flow field of this system. In the simulation, the effect of the rotating front rollers on the flow field is taken into consideration. Flow characteristics inside the spinning nozzle, flow field of the front rollers, and streamline patterns have been revealed. The results show that a high-speed swirling flow is generated in the near-wall region in the nozzle chamber due to the ejection of air-jets from the tangential injectors. An asymmetric sub-pressure zone is formed in the core region of the nozzle chamber where the interactions of the high-speed swirling flow and three streams of secondary flows generate three vortices. Airflows in the vicinity of the front rollers generally converge toward the nozzle entrance from all directions except those in the boundary layer of the front roller surfaces, which is helpful for the delivery of fibers into the nozzle. A vortex is formed above the top roller and another beneath the bottom roller. The results of the streamline patterns show that the flow characteristics of the modified vortex spinning can facilitate the formation process of the core-spun yarn, which presents a qualitative explanation to the dynamic behavior of the fibers that was experimentally obtained.

Time-dependent analysis of electroosmotic fluid flow in a microchannel

The present work models electroosmotic induced fluid flow in a microfluidic device. For theoretical analysis, the geometry of this device is considered as an asymmetric, narrow, wavy channel with charged surface. It is assumed that the length of the channel is finite and the characteristic wavelength is very large compared to the half width of the channel. The flow is assumed to be governed by Navier–Stokes equations augmented with electric body force. A transient two-dimensional flow analysis is presented by employing lubrication theory. Debye–Huckel linearization is adopted to obtain a general solution of Poisson–Boltzmann equation. The flow rate, velocity profile, pressure distribution, and wall shear stress are analyzed as functions of various parameters involved like zeta-potential ratio, Debye–Huckel parameter, etc. It is noted that the fluctuations in pressure and shear stress increase with the increasing zeta-potential ratio when the Helmholtz–Smoluchowski velocity is positive. The streamline pattern and the particle trajectories are analyzed to understand the trapping phenomenon and the retrograde motion. It is observed that the electroosmosis phenomenon drastically modulates the fluid flow in microchannels. Although the asymmetric nature of the wavy channel does not support active particle transport, the applied electric field enhances the particle motion favoring optimal conditions. It is observed that the extreme asymmetry of the wall motility reduces the net flow rate. Further, it is noticed that the asymmetry reduces the amplitudes of the pressure. This model can help toward designing artificial organs based on microfluidic devices which can also be applicable to analyze lumenal flow inside arteries and flow inside intrauterine system, and to implant the embryo at the best location in the uterus for human-assisted reproduction.

Effect of spacing on laminar natural convection flow and heat transfer from two spheres in vertical arrangement

Laminar natural convection heat transfer from two vertically arranged spheres has been investigated numerically in air (Pr=0.72) for large Rayleigh number (Ra=105). The effect of sphere spacing (S) on fluid flow and heat transfer is comprehensively analyzed within the ratio of spacing to radius (S/R) ranging from 4 to 48, i.e., 2⩽S/D⩽24. Extensive results are obtained for complete descriptions on natural convection of two-sphere system, such as the streamline patterns and isotherm contours, dimensionless velocities and temperature profiles, drag coefficient, local and average Nusselt numbers. Comparisons with the isothermal bisphere have also been reported with the previous studies. Due to the interaction of preheating effect and flow mixing, the lower sphere has a great influence on the fluid flow and heat transfer around the upper sphere with the change of spacing between the two spheres. The variation of dimensionless temperature with the dimensionless distance between the two spheres has been also concluded to explain the impact of preheating effect. Finally, correlations have been developed for accurate prediction of natural convection heat transfer for each single sphere and the whole two-sphere system, which can be applied to relevant engineering calculations, and provide values for academic research.

FLUID FLOW CHARACTERISTICS IN DOUBLE-SIDED LID-DRIVEN MICROCAVITY USING LATTICE BOLTZMANN METHOD

In this study, we analyze the fluid flow characteristic of rarefied gas flows in double-sided lid-driven microcavity subjected to various combinations of boundary conditions that simulate the slip at the walls using lattice Boltzmann method (LBM) constituting a single relaxation time (SRT) model. The fluid motion inside a closed square container with two rigid walls and two moving walls constitutes an exemplar for internal vortex flows. First, a complicated geometry, namely, the single-sided lid-driven microcavity is studied using the LBM-SRT model. Next, this code is extended to simulate flows in a double-sided microcavity flow. Numerical computation of fluid flow incorporating various slip boundary conditions as bounce-back and specular boundary condition (BSBC) for different values of tangential accommodation momentum coefficient (TMAC) has been investigated. Various values of Knudsen number in the slip and transition regime (Kn = 0.01, 0.05, 0.10, 0.135, and 0.15) along with different aspect ratios of 0.33, 0.50, 1.0, 2.0, and 3.0 have been considered in this study. The streamline patterns and velocity profiles were obtained for different Knudsen numbers. The formation and movement of primary vortices have been well captured with the variation of Knudsen numbers for different aspect ratios of microcavity.

STRUCTURAL BIFURCATION OF DIVERGENCE-FREE VECTOR FIELDS NEAR NON-SIMPLE DEGENERATE POINTS WITH SYMMETRY

In this study, topological features of an incompressible two-dimensional flow far from any boundaries is considered. A rigorous theory has been developed for degenerate streamline patterns and their bifurcation. The homotopy invariance of the index is used to simplify the differential equations of fluid flows which are parameter families of divergence-free vector fields. When the degenerate flow pattern is perturbed slightly, a structural bifurcation for flows with symmetry is obtained. We give possible flow structures near a bifurcation point. A flow pattern is found where a degenerate cusp point appears on the x-axis. Moreover, we also show that bifurcation of the flow structure near a non-simple degenerate critical point with double symmetry is generic away from boundaries. Finally, we give an application of the degenerate flow patterns emerging when index 0 and -2 in a double lid driven cavity and in two dimensional peristaltic flow.

A Class of Exact Solutions for a Variable Viscosity Flow with Body Force for Moderate Peclet Number ViaVon-Mises Coordinates

The objective of this article is to communicate a class of new exact solutions of the plane equation of momentum with body force, energy and continuity for moderate Peclet number in von-Mises coordinates. Viscosity of fluid is variable but its density and thermal conductivity are constant. The class characterizes the streamlines pattern through an equation relating two continuously differentiable functions and a function of stream function ψ. Applying the successive transformation technique, the basic equations are prepared for exact solutions. It finds exact solutions for class of flows for which the function of stream function varies linearly and exponentially. The linear case shows viscosity and temperature for moderate Peclet number for two variety of velocity profile. The first velocity profile fixes both the functions of characteristic equation whereas the second keeps one of them arbitrary. The exponential case finds that the temperature distribution, due to heat generation, remains constant for all Peclet numbers except at 4 where it follows a specific formula. There are streamlines, velocity components, viscosity and temperature distribution in presence of body force for a large number of the finite Peclet number.

Numerical study of unsteady MHD flow of Williamson nanofluid in a permeable channel with heat source/sink and thermal radiation

The present research work is dedicated to examine the heat and mass transport phenomenon due to unsteady MHD flow of Williamson nanofluid between the permeable channel with heat source/sink. The influence of buoyancy and thermal radiation effects are also considered for the present model. The flow equations are reduced to an equivalent nonlinear coupled partial differential equations (PDE) through suitable transformation. The numerical simulation is performed to attain the solution of the nonlinear system via the Crank-Nicolson finite difference scheme. The influence of various emerging parameters on velocity, temperature and concentration profiles are developed. The magnetic parameter plays the significant role to enhance the heat transfer rate but reduces the velocity profile. The velocity of the fluid increases gradually with respect to time and this influence is dominant at the center of the channel. Additionally, the velocity profile exhibits the increasing behavior by varying the Reynolds number for a small time. In the entire study it is analyzed that the temperature profile increases for increasing values of Reynolds, thermophoresis, Brownian motion and heat source numbers, while a low temperature profile is attained for Biot numbers. The thermophoresis and Brownian motion parameters provide the decreasing concentration profile however, an increasing result is noticed for Biot numbers. An increase in the values of Williamson parameter $ \Lambda$ , illustrates the increase effects on the skin friction coefficient when $ \eta=1$ while it shows the decrease behavior at $ \eta=0$ . The effects of the Reynolds number on streamlines pattern is presented. It is noticed that the higher values of Re affects the stream line pattern.

Shear Flows Accelerate Mixing Dynamics in Hyporheic Zones and Hillslopes

AbstractTopographic relief and river bedforms generate nested streamline patterns, which drive the propagation and mixing at depth of changes in surface water concentration or temperature. While concentration distributions and biogeochemical reactions in such flow cells are often studied under steady state transport conditions, there is increasing evidence that transient mixing processes may have a significant contribution to effective mixing and reaction rates. Here we show that these streamline patterns act as shear flows, which significantly accelerate mixing dynamics within flow cells and can lead to the formation of transient mixing hot spots at depth. We provide analytical solutions that quantify the dynamics of mixing in a flow cell for a pulse and a front initial solute distribution, which represent two idealized end‐members of more complex solute distributions in natural systems. These results provide new insights into the patterns and dynamics of mixing at hyporheic zone, hillslope, and catchment scales.

Heat Transfer Enhancement of a Flat Plate Boundary Layer Distributed by a Square Cylinder: Particle Image Velocimetry and Temperature-Sensitive Paint Measurements and Proper Orthogonal Decomposition Analysis

The current empirical study was conducted to investigate the wall neighborhood impact on the two-dimensional flow structure and heat transfer enhancement behind a square cylinder. The low- velocity open-circle wind tunnel was used to carry out the study tests considering the cylinder diameter (D)-based Reynolds number (ReD) of 5130. The selected items to compare were different gap height (G/D= 0.0, 0.1, 0.2 and 0.8). The flow field was measured using particle image velocimetry (PIV) with high image-density camera. The PIV-derived time-averaged quantities, including the streamline pattern, streamwise velocity fluctuation intensity, and reverse-flow intermittency, were examined for the flow past the square cylinder. The measurements of PIV were decomposed with the help of proper orthogonal decomposition (POD) approach that provides a proper view of the POD modes. To obtain the value of the heat transfer enhancement behind the square cylinder, the full-field temperature distributions of flat plate were measured through the temperature-sensitive paint (TSP) technique. Results showed that the maximum heat transfer enhancement was obtained at G/D=0.2 due to the high unstable flow near the wall.

Viscous Fluid Flows Induced by Translational-Oscillatory Motion of a Submerged Porous Sphere

Viscous fluid flows induced by a translational-oscillatory motion of a submerged porous sphere are determined. The fluidmotion inside and outside the sphere is considered in amoving noninertial reference frame fitted to the sphere. Exact analytical solutions of the Navier–Stokes equation outside the sphere and the nonstationary Brinkman equation inside the sphere are found. Examples of streamline patterns for some values of governing parameters are presented. It is shown that the results obtained earlier for particular cases of viscous flow around an impermeable solid sphere can be obtained from the solution presented.

Numerical Analysis on Effect of Jet Injection on Vortex Shedding for Flow Over a Circular Cylinder

Two-dimensional numerical investigations on the flow characteristics past a circular cylinder with a jet injection at the rear stagnation point are performed. Transient, incompressible, laminar, and isothermal flow governing equations are solved with finite volume method. Numerical simulations have been carried out at a Reynolds number of 150 with different injection ratios (IR) ranging from 0.5 to 7. Time evolutions of the coefficients of drag and lift, and streamline patterns are plotted. Three different flow pattern ranges are observed, namely wake dominant (IR $$\,=\,$$ 0–1.5), transition (IR $$\,=\,$$ 1.5–2.5) and jet dominant (IR > 2.5), and they are characterized by the combined effects of vortex shedding, undulation and jet dominant phenomena appearing in the flow downstream. It is also found that $$C_{\mathrm{d}}$$ decreases slightly with the injection ratio up to 1.5, after that it monotonically increases with the injection ratio. The similar incremental trend is observed in the Strouhal number variation with IR up to 1.5; then, it increases almost linearly till IR $$\,=\,$$ 4. When IR is greater than 4, there is a sudden drop in the Strouhal number value equal to zero and it remains constant after that for all the IR values considered in this study. The power spectral density of $$C_{\mathrm{l} }$$ indicates that the dominant frequency is present for the lower IR up to 4 and that no dominant frequency appears in the higher injection ratio range of 5–7 due to a complete suppression of the vortex shedding behind the cylinder by a dominant jet mechanism.

Natural convection heat transfer in a power-law fluid from a heated rotating cylinder in a square duct

Laminar natural convection heat transfer in a power-law fluid from an isothermal rotating cylinder placed coaxially in a square duct has been studied numerically over the following ranges of conditions: Grashof number (10⩽Gr⩽103); Prandtl number (0.72⩽Pr⩽100); power-law index (0.2⩽n⩽1.5) and non-dimensional rotational velocity (0⩽S⩽4). The spatial variation of the velocity and temperature fields are visualised in terms of the streamline and isotherm patterns, and temperature and vertical velocity at a few locations, respectively. Indeed, a range of flow patterns including twin-celled and single-celled recirculating regions can be observed depending upon the relative strengths of the buoyancy-induced and forced flow. The rate of heat transfer is described in terms of the distribution of the local Nusselt number over the surface of the cylinder together with its surface averaged value. As expected, the mean Nusselt number shows a positive dependence on the both Grashof and Prandtl numbers irrespective of the values of the power-law index and rotational velocity. For a non-rotating cylinder (S = 0), shear-thinning fluid behaviour promotes heat transfer, whereas shear-thickening viscosity impedes it with reference to that in Newtonian fluids otherwise under identical conditions. For the case of a rotating cylinder (S≠0), the rotation has positive influence on the rate of heat transfer at low values of the Grashof or Rayleigh number (Ra<500) irrespective of the type of fluid behaviour, i.e., shear-thinning or shear-thickening or Newtonian. However, at high values of the Grashof or Rayleigh numbers, the gradual increase of rotation of the cylinder first lowers the rate of heat transfer, and then increases it for shear-thickening (n > 1) and Newtonian fluids (n = 1). On the other hand, a reverse trend is seen for shear-thinning fluids. These non-monotonous trends in the overall heat transfer stem from the interactions between the rate of variation of the fluid viscosity and the temperature gradient on the surface of the cylinder. Therefore, a prudent choice of the operating conditions and the fluid behaviour can be used to regulate the rate of heating or cooling from a rotating cylinder. Finally, the present values of the average Nusselt number are correlated in order to facilitate the interpolation of the present results for the intermediate values of Gr, Pr, S and n and/or the estimation of heat transfer duty in a new application.

Physiological analysis of streamline topologies and their bifurcations for a peristaltic flow of nano fluid

In the present article, the techniques of dynamical systems are utilized to investigate the streamline patterns along their bifurcations for peristaltic flow under mixed convection effect. Here the peristaltic flow is discussed in a vertical channel. The flow is considered in a two-dimensional symmetric channel as well as an axisymmetric tube. We have evaluated the peristaltic flow of blood base nanofluid. The momentum equations are reduced by employing approximation of low Reynolds number and long wavelength. For the discourse of the path of particle in the wave frame, an arrangement of nonlinear independent differential equations are built up and the strategies for dynamical frameworks are utilized to examine the local bifurcations and their topological changes. Critical points classifications were made by scrutiny of the eigenvalues of the Jacobian matrix. This principle are utilized to divulge the local bifurcation of the critical points encountered for different flow situations. Flow situations marked as: backward flow, trapping or augmented flow. The analysis is disclosed that the number and size of trapped bolus increases in planner channel and decline in axisymmetric channel by increasing Grashof number. Moreover, the decreasing behaviour of temperature is depicted, which clarify the nanofluid as a cooling agent. Graphically, a wide range of topological changes of bifurcations are examined. At long last, to outline the bifurcation the diagram of global bifurcation is utilized.

Streamline Topology of Axisymmetric Flow Near Non-Simple Singular Point

The aim of this paper is to obtain streamline patterns of axisymmetric flow and their bifurcations for 2-D incompressible flows close to non-simple singular point. The streamlines of a Hamiltonian vector field system are simplified by using the homotopy invariance of the index theory. Using a homotopy invariance of the index, we develop a theory for the sufficient and necessary conditions for structural bifurcation of axisymmetric flow near non-simple degenerate critical points. The variation of parameters in the flow field can cause structural bifurcations. The bifurcation of the degenerate flow structure is obtained when it is perturbed slightly.

Qualifying the design of a floating closed-containment fish farm using computational fluid dynamics

In order to overcome the environmental consequences of traditional net pens in producing Atlantic salmon, closed containment aquaculture systems are being developed, where the culture volume is separated from the ambient environment by an impermeable wall. However, several challenges in terms of construction and hydrodynamic properties must be solved before such systems can be used on a large scale. A study was thus performed on the design of a floating closed-containment fish farm in sea. This paper presents the design and flow analysis of two versions of the globe; first is the pilot design of a 74 m3 globe, and the second is the design of a 3500 m3 globe for post-smolts of Atlantic salmon. The results of turbulence model of the pilot globe were validated against the velocity measurements using acoustic Doppler velocimetry. Computational assessment of various flow characteristics includes the velocity and vorticity fields. The streamline pattern confirmed the secondary vortices, creating the tea-cup hydrodynamics. Coherent vortices, identified by means of Q-criterion, show the presence of vortex column in the globe. Two inlet configurations were tested on the post-smolt globe for improved performance. Design 1 has the standard one-column nozzle configuration, and the Design 2 has two-column nozzles to create a V-shaped inflow. The mixing action of the two designs was examined using Lagrangian particle tracking. Considerable influence of inlet configuration on the particle motion was observed. It was found that V-nozzles (two columns of inlet nozzles) are more effective than standard nozzles in flushing the solid particles.

Unsteady Peristaltic Transport of a Particle-Fluid Suspension: Application to Oesophageal Swallowing

Abstract This model characterises the flow behaviour of suspended particles when swallowing through oesophagus. Transport of particle-fluid mixture induced by dilating peristaltic waves on a circular cylindrical tube was considered for investigation. Unsteady closed-form solutions for pressure gradient, velocity and stream function are obtained by applying regular perturbation technique up to the first order of wavenumber (the ratio of the tube radius to the wavelength). It is observed that the axial velocity of the fluid is greater than that of the solid particles almost everywhere. However, at the wall the axial velocity of the fluid is zero due to the no-slip condition imposed on it; but the suspended particulate material has non-zero positive axial velocity. Thus, the axial velocity of the suspended particles near the tube wall is more than that of the fluid velocity. It is further observed that the axial velocity is negative in the regions close to maximum occlusions giving way to instantaneous backward flow. It is also inferred that the maximum axial velocity of the particle-fluid suspension with non-zero wavenumber is more than that of the particle-free fluid with zero wavenumber. We examined the effect of volume fraction of suspended particulate matter on pressure gradient and velocity. An increase in the volume fraction diminished the pumping performance and also the axial and radial velocities. The results are also compared with those which were obtained for zero wavenumber. The outcome of the investigation endorses the doctors’ advice to patients suffering from achalasia, oesophageal stricture and oesophageal tumors to take liquid or food items with lesser solid contents. Streamline patterns are changed by increasing the flow rate while trapping occurs at high flow rates.

Nanoparticles (Cu, [formula omitted], [formula omitted]) analysis on unsteady blood flow through an artery with a combination of stenosis and aneurysm

A theoretical and numerical study of unsteady pulsatile blood flow through an artery with a combination of stenosis and aneurysm containing nano-particles (Cu, TiO2,Al2O3) has been discussed in this article. The transport equations comprise momentum and energy partial differential equations with physiologically realistic boundary conditions. The bi-directional, non-linear, coupled differential equations are simplified by using the assumption of mild stenotic condition. The coupled differential equations are solved numerically by using robust finite difference method. The effects of nano-particles along with aneurysm on blood flow rate, wall shear stress and impedance are discussed in detail through graphs. Similarly, the graphical results of nano-particles fluid show notable deviation when compared with pure blood profiles. At the end, it is also concluded from the calculated results that both source/sink β parameter and Grashof number (Gr) facilitates the blood to maximize its flow within the vessel and minimize the hemodynamic factors such as wall shear and impedance. The circulating regions inside the flow field are also investigated through instantaneous patterns of streamlines for different parameters of interest.

CFD modeling and sensitivity analysis of heat transfer enhancement of a ferrofluid flow in the presence of a magnetic field

In this paper, a numerical method is developed to simulate the effect of an external magnetic field on convection heat transfer of a ferrofluid flow inside a rectangular duct. This model is two-dimensional, steady-state, laminar and incompressible. Simple finite volume method is used to couple and solve continuity, momentum and energy equations. In the first part of this paper, it is observed that ferrofluid particles movement along the magnetic field of a line dipole changes the streamline patterns and enhances heat transfer. In the second part of this paper, a sensitivity analysis is performed to investigate the effects of Reynolds number, magnetic field strength, location, and number of line dipoles on the convection heat transfer. It is observed that cooling rate is higher at larger Reynolds numbers while increasing magnetic field strength would not necessarily result in noticeable improvement in heat transfer. It is also noticed that magnetic field strength should be large enough to merge small vortexes and to create large circulation zones inside the duct. Our simulation also revealed that heat transfer could be augmented by adding line dipoles on high-temperature regions closer to the duct inlet.

Flow Structure in a Ranque−Hilsch Vortex Tube

The structure of twisted flow in a Ranque−Hilsch vortex tube is investigated experimentally by modeling gas flow with an incompressible fluid flow. The velocity field is measured with a laser Doppler anemometer in the entire volume of the vortex chamber. The streamline pattern, which gives a complete presentation of the flow structure in the Ranque−Hilsch tube, is plotted in the axial section of the chamber. The resulting streamline pattern can serve as a basis for explaining the physical mechanism of the Ranque effect.

3D Model of Generalized Power Law Blood Flow in a Stenosed Bifurcated Artery

Numerical simulation of the behaviour of blood flow through a stenosed bifurcated artery with the presence of single mild stenosis at parent artery is investigated. The flow analysis applies the incompressible, steady, three-dimensional Navier-Stokes equations for non-Newtonian generalized power law fluids. Behaviour of blood flow is simulated numerically using COMSOL Multiphysics that based on finite element method. The results show the effect of severity of stenosis on flow characteristics such as axial velocity and its exhibit flow recirculation zone for analysis on streamlines pattern.