Streamline Patterns Research Articles

CFD Investigation of Mechanical Heart Valve Orientations in Modulating Left Ventricular Hemodynamics

This study provides a comprehensive computational analysis of how mechanical heart valve orientations impact left ventricular (LV) hemodynamics, with potential implications for surgical valve placement. Focusing on monoleaflet valves (MLV) and bileaflet valves (BLV), the research explores how different valve angles influence blood flow patterns within the LV chamber. The analysis includes velocity contours, streamline patterns, vorticity contours, and temporal velocity fluctuations to elucidate the effects of valve orientation on LV performance. Findings indicate that valve orientation significantly influences flow coherence and blood velocity. For instance, a 20-degree orientation in the MLV alters jet flow in ways that could affect wall shear stress distribution. At a 45-degree angle, the MLV produces a more centralized jet flow, enhancing flow uniformity and aligning more closely with physiological conditions. In contrast, a 55-degree angle skews the jet flow, potentially leading to adverse hemodynamic effects. Similarly, BLV orientations at 45, 55, 60, and 70 degrees showed that lower angles improved flow efficiency, reducing energy losses and minimizing the risk of regurgitation, while higher angles led to turbulent and potentially damaging flow patterns. Comparative results at a 45-degree orientation demonstrated the superior performance of BLV in regulating normal velocity, with BLV reducing average blood velocity by 38.77% compared to a 29.53% reduction with MLV. These results underscore the importance of optimizing mechanical heart valve orientations to enhance left ventricular hemodynamics. The findings carry significant clinical implications, supporting evidence-based valve placement decisions that can substantially improve patient outcomes, survival rates and long-term cardiovascular health.

Solving the Small Disturbance Equation and Numerical Method Optimization in Subsonic and Supersonic Flows

This paper addresses the solution of the Small Disturbance Equation (SDE) under subsonic and supersonic flow conditions using Successive Over-Relaxation (SOR) techniques. The study implements and validates numerical methods tailored to the unique dynamics of these regimes by setting precise boundary conditions, adjusting computational stencils, and managing the Mach number ( M∞ ) across the solution domain. A detailed comparison of streamline patterns between the regimes illustrates the efficacy of the applied numerical strategies. In the subsonic domain, the flow demonstrates uniform and smooth characteristics, conducive to standard SOR techniques, as evidenced by the rapid decline in residual errors, confirming the method’s efficiency for accurate solutions. Conversely, the supersonic regime presents increased complexity where standard finite difference methods encounter notable challenges, necessitating more sophisticated approaches to capture the intricate flow behaviors effectively. Conversely, in the supersonic regime, where the flow behavior exhibits more complex characteristics, the standard finite difference method faces challenges.

Flow field analysis of self-sustained flutter of a wide-slotted bridge deck

This study delves into the flutter mechanism of a 5,000 m bridge with a wide-slotted deck, finding that the motion is self-sustained and not violently destructive. The system damping ratio is not fixed, and only one stable orbit exists. High-resolution PIV experiments at an experimental wind speed of 10.5 m/s measured the static and dynamic flow fields on the windward and leeward decks. The static results showed leading-edge separation on the windward deck within the reference range, while separation on the leeward deck was difficult to observe. Dynamic testing identified instantaneous vortices around the windward/leeward deck at each phase, with no signs of vortices in the wind speed vectors at all phases after phase-averaging, indicating that the vortex drift hypothesis is not valid. The analysis of the streamline pattern revealed periodic variations in leading-edge separation size and reattachment length on the windward deck during the vibration process, while the leeward deck showed consistently inconspicuous changes. Further examination uncovered a peculiar behavior in the horizontal wind speed profile on the leeward deck during the vibration process, attributed to dynamic changes in the height difference between the windward and leeward decks during flutter. The study suggests that the unusual wind speed profile on the leeward deck is caused by the dynamic changes in height difference between the windward and leeward decks during the flutter process, resulting in additional wind loading. These findings shed light on the complex dynamics of bridge flutter and have implications for the design and maintenance of long-span bridges.

Magnetohydrodynamic double diffusion natural convection of power-law Non-Newtonian Nano-Encapsulated phase change materials in a trapezoidal enclosure

PurposeThe present numerical investigation examines the magnetohydrodynamic (MHD) double diffusion natural convection of power-law non-Newtonian nano-encapsulated phase change materials (NEPCMs) in a trapezoidal cavity.Design/methodology/approachThe governing Navier-Stokes, energy and concentration equations based on the Cartesian curvilinear coordinates are solved using the collocated grid arrangement’s finite volume method. The in-house FORTRAN code is validated with the different benchmark problems. The NEPCM nanoparticles consist of a core-shell structure with Phase Change Material (PCM) at the core. The enclosure, shaped as a trapezoidal hollow, features a warmed (Th) left wall and a cold (Tc) right wall. Various parameters are considered, including the power law index (0.6 ≤ n ≤ 1.4), Hartmann number (0 ≤ Ha ≤ 30), Rayleigh number (104 ≤ Ra ≤ 105) and fixed variables such as buoyancy ratio (Br = 0.8), Prandtl number (Pr = 6.2), Lewis number (Le = 5), fusion temperature (Θf = 0.5) and volume fraction (ϕ = 0.04).FindingsThe findings indicate a decrease in local Nusselt (Nu) and Sherwood (Sh) numbers with increasing Hartmann numbers (Ha). Additionally, for a shear-thinning fluid (n = 0.6) results in the maximum local Nu and Sh values. As the Rayleigh number (Ra) increases from 104 to 105, the structured vortex in the streamline pattern is disturbed. Furthermore, for different Ra values, an increase in n from 0.6 to 1.4 leads to a 67.43% to 76.88% decrease in average Nu and a 70% to 77% decrease in average Sh.Research limitations/implicationsThis research is for two-dimensioal laminar flow only.Practical implicationsPCMs represent a class of practical substances that behave as a function of temperature and have the innate ability to absorb, release and store heated energy in the form of hidden fusion enthalpy, or heat. They are valuable in these systems as they can store significant energy at a relatively constant temperature through their latent heat phase change.Originality/valueAs per the literature review and the authors’ understanding, an examination has never been conducted on MHD double diffusion natural convection of power-law non-Newtonian NEPCMs within a trapezoidal enclosure. The current work is innovative since it combines NEPCMs with the effect of magnetic field Double diffusion Natural Convection of power-law non-Newtonian NEPCMs in a Trapezoidal enclosure. This outcome can be used to improve thermal management in energy storage systems, increasing safety and effectiveness.

Study of the impurity dissolution kinetics, rheological characterization, and hydrodynamic aspects during the bioleaching of iron ore pulp in a bioreactor

AbstractThis research aims to study the rheological behavior and impurities dissolution kinetics in a bioleaching process of two particle sizes and three different pulp densities, which are analyzed and compared. It was found that the small particle size with 40% (w/w) pulp density provides the maximum dissolution of impurities in the shortest bioleaching time (in 2 days). Furthermore, through a CFD simulation in a system with 40% (w/w) pulp density and 44 μm particle size, a stirring speed of 700 rpm provides the best mixing conditions in the bioreactor, enabling good distribution of recirculation zones and adequate streamline patterns with a viscosity map that minimizes regions of high and low viscosity. Graphical abstract

Analysis of a Bifurcation and Stability of Equilibrium Points for Jeffrey Fluid Flow through a Non-Uniform Channel

This study aims to analyze how the parameter flow rate and amplitude of walling waves affect the peristaltic flow of Jeffrey’s fluid through an irregular channel. The movement of the fluid is described by a set of non-linear partial differential equations that consider the influential parameters. These equations are transformed into non-dimensional forms with appropriate boundary conditions. The study also utilizes dynamic systems theory to analyze the effects of the parameters on the streamline and to investigate the position of critical points and their local and global bifurcation of flow. The research presents numerical and analytical methods to illustrate the impact of flow rate and amplitude changes on fluid transport. It identifies three types of streamline patterns that occur: backwards, trapping, and augmented flow resulting from changes in the value of flow rate parameters.

The effect of slip parameter in an axisymmetric oscillatory Stokes flow

A general solution of Stokes equations for the problem of an axisymmetric oscillatory flow of an incompressible, viscous fluid past a sphere satisfying general boundary conditions is obtained. The behavior of the magnitude of drag is observed with the variation of the slip parameter. Some more interesting behaviors are detailed, and several existing results pertaining to steady flows and flows with rigid and shear free boundary conditions are recovered as special cases. The corresponding results are discussed for four different axisymmetric oscillatory Stokes flows, namely, uniform flow, flows generated due to a dipole, a source, and a Stokeslet. A few interesting streamline patterns like formation, elongation, and disappearance of viscous eddies in the vicinity of the sphere with a periodic reversal of the flow are observed at different frequencies for different values of the slip parameter.

P-wave velocity evolution and interpretation of seepage mechanisms during CO2 hydrate formation in quartz sands: Perspective of hydrate pore habits

The hydrate-based CO2 storage (HBCS) is a promising technology for controlling CO2 emissions. A comprehensive understanding of the hydrate pore habits and seepage mechanism of hydrate-bearing sediments (HBSs) could provide a theoretical basis for HBCS. In the study, the hydrate occurrence characteristics, water migration and P-wave velocity response during hydrate formation in quartz sands are investigated. In addition, a new theoretical equation that relates P-wave velocity to permeability is presented. The digital core of porous media containing hydrate is also established, and the seepage characteristics during hydrate formation are revealed by numerical simulation. The results show that hydrates are preferentially generated in large pores and initially appear in a non-cementing pore-filling pattern, while an annular flow path for water is formed in quartz sands during hydrate formation. The hydrate morphology is changed from a pore-filling pattern to a patchy pattern at a critical hydrate saturation of around 3–7% for quartz sands with various particle diameters. The formation sites and spatial heterogeneity of hydrates can be depicted by the evolution pattern of streamlines. The results of the experiments indicate that the new semiempirical model is effective for estimating the permeability from the P-wave velocity of HBSs. These findings offer significant theoretical and practical insights for HBCS in porous media.

Dynamics of elevated dodecane jets in crossflow at supercritical pressure

In advanced aero-engines, kerosene is often transversely injected into the combustor at supercritical pressure, where the shorter jet penetration depth may result in poor mixing and the local hot spots near the combustor wall. Elevating the jet nozzle is proposed to remedy these issues, where the flowfield complexity increases as a result of the intricate interactions among the jet, crossflow, and stack wake. The distinct flow dynamics of elevated dodecane jets in crossflow (EJICF) at supercritical pressure are numerically investigated using large eddy simulation. The effects of various parameters, including ambient pressure, elevation stack thickness, and stack height are studied. The results reveal that, the jet-wake recirculation bubble is prominently evident at low supercritical pressure, attributed to the strong real-fluid effect resulting from significant density stratification in the jet's upstream shear layer. Analysis of streamline patterns and vorticity budgets underscores the role of the real-fluid effect in delaying the shift of the flow pattern from the transitional regime to the jet-dominated regime. Increasing stack thickness mitigates the impact of jet upshear effects and has the potential to eliminate the lock-in phenomena between jet wake and stack wake. A reduction in stack height leads to the diminishment of the stack wake vortex shedding. In contrast to conventional JICF, the EJICF configuration exhibits a heightened tendency for recirculation bubble formation in the jet wake region. An analysis of spatial mixing deficiencies demonstrates that incorporating an elevation stack with proper thickness and height can dramatically improve the jet-crossflow mixing efficiency.

Kinetically anisotropic Hamiltonians: plane waves, Madelung streamlines and superpositions

A Hamiltonian in two space dimensions whose kinetic-energy contributions have opposite signs is studied in detail. Solutions of the time-independent Schrödinger equation for fixed energy are superpositions of plane waves, with wavevectors on hyperbolas rather than circles. The local velocity (e.g. in the Madelung representation) is proportional to the kinetic momentum, i.e. local particle velocity, not the more familiar canonical momentum (phase gradient). The patterns of the associated streamlines are different, especially near phase singularities and phase saddles where the kinetic and canonical streamline patterns have opposite indices. Contrasting with the superficially analogous circular smooth solutions of kinetically isotropic Hamiltonians are wave modes that are anisotropic in position and also discontinuous. Pictures illustrating these phenomena are included. The occurrence of familiar concepts in unfamiliar guises could be useful for teaching quantum or wave physics at graduate level.

Numerical study of energy consumption in spacer-filled feed channels through 3D inverse modeling and computational fluid dynamics

This project employs advanced Computational Fluid Dynamics (CFD) simulations to investigate the complex flow field dynamics within the channel of membrane module featuring a commercially available feed spacer. Utilizing Micro-CT scanning, the intricate three-dimensional (3D) structure of the spacer is accurately captured, enhancing the precision of the simulation models. The project focuses on the effects of varying Reynolds number (Re) and Aspect Ratio (AR) on the energy consumption within the feed channel of membrane module, analyzing streamline patterns, vorticity, and flow separation angles in detail. Findings indicate that the total enstrophy identification method effectively pinpoints areas of high energy consumption, especially at lower Re levels where flow separation significantly contributes to hydraulic losses. As Re increases, the separation vortex shifts rearward, resulting in a marked decrease in the energy consumption coefficient. Furthermore, the flow separation angle consistently declines with increasing Re, stabilizing at higher levels. Significantly, a reduction in AR from 1.015 to 0.725 more than doubles the decrease in flow separation angle, highlighting substantial potential energy savings through spacer design optimization. These insights are crucial for improving the design and efficiency of spiral wound membrane modules and for refining feed spacer configurations to enhance performance.

Evaluation of Heat Transfer and Fluid Dynamics across a Backward Facing Step for Mobile Cooling Applications Utilizing CNT Nanofluid in Laminar Conditions

In a variety of engineering applications, the efficacy of heat dissipation in mobile cooling systems is greatly influenced by the Backward Facing Step. Its significance in optimizing cooling solutions for mobile devices is highlighted by the fact that its design and fluid dynamics are crucial in minimizing skin friction and improving passive heat transfer. In this paper, we present a verification of an advanced numerical model for heat transfer and fluid flow through a Backward Facing Step, used in mobile cooling. The objective of this study is to explore fluid separation, a method enhancing passive heat transfer and reducing skin friction. ANSYS/FLUENT software has been used to solve the backward facing step in a horizontal duct filled with pure water. Carbon nanotube (CNT) dispresed into the base fluid at different volume fractions of 0.2%, 0.65%, and 1%. This study focused on laminar flow conditions ranging from Reynolds numbers 200 to 900. In order to reduce the computation time and ensuring the accuracy and reliability of numerical simulations, a grid independence study has been conducted. The findings revealed a substantial rise in the average Nusselt number and heat transfer coefficient with increased Reynolds number and volume fraction of nanoparticles. Specifically, the nanofluid (CNT/water) exhibited the highest average Nusselt number and heat transfer coefficient with volume fractions 1%. Furthermore, the research showed a decrease in the skin friction factor as both Reynolds number increased and nanoparticles’ volume fraction decreased. The increments of nanoparticles' concentrations lead to increase viscosity, promotes agglomeration, alters flow behaviour by inducing turbulence, and enhances heat transfer. These factors collectively contribute to higher skin friction due to increased resistance to fluid flow and disrupted streamline patterns

Numerical simulation of flow over short crested weirs - case study: Quarter-circular crested weir

In this study, the flow characteristics over a quarter-circular crested spillway (QCCS) were investigated using computational fluid dynamics (CFD) simulations. The simulations included an in-depth analysis of parameters such as flow velocity, pressure distribution, and streamline patterns. The RNG turbulence model was used to simulate the flow field and hydraulic characteristics. In particular, the simulations were performed at the design discharge. The numerical results were carefully compared with laboratory observations, showing that there is good agreement between the simulated results and the observed data. The results of the numerical simulation showed that the streamlines are completely in line with the curvature of the crest and that there is no separation zone (separation of the streamlines from the surface of the crest). furthermore, there is no negative pressure zone along the crest, which means that the risk of cavitation is eliminated. The highest value of velocity and the lowest pressure of flow occur at the outlet end of the crest.

Micropolar Fluid Flows Past a Porous Shell: A Model for Drug Delivery Using Porous Microspheres

The creeping flow of an incompressible, bounded micropolar fluid past a porous shell is investigated. The porous shell is modeled using a Darcy equation, sandwiched between a pair of transition Brinkman regions. Analytical expressions for the stream function, pressure, and microrotations are given for each region. Streamline patterns are presented for variations in hydraulic resistivity, micropolar constants, porous layer thickness, and Ochoa-Tapia stress jump coefficient. An expression for the dimensionless drag for the unbounded case of the system is presented, and its variation with hydraulic resistivity and porous shell thickness is presented. The unbounded case represents a theoretical model for oral drug delivery using porous microspheres. It was found that optimal circulation between the porous region and the outer fluid occurred for low values of hydraulic resistivity and for a complete porous sphere.

A multi-region analysis of unsteady Oseen's equation for accelerating flow past a circular cylinder

It is difficult to find a valid high-order (of Reynolds number) analytical approximation to the uniform viscous flow past an infinite circular cylinder by applying perturbation techniques. In this study, we show that by accelerating flow past a circular cylinder with taking unsteady Stokes' solution as an initial approximation, higher-order approximation solutions to unsteady Oseen's equation can be obtained by an iteration scheme of perturbation, which exactly satisfy the boundary conditions. As a matter of fact, the nonlinear (convective) term linearized by Oseen's approximation is overweighted especially near the body surface. To eliminate the overweight, a multi-region analysis is proposed in this study to improve analytical unsteady Oseen's solution so as to extend the valid range of Reynolds numbers. In other words, the flow region is hypothetically divided into several annular regions, and the linearized convective term in each region is modified by multiplying with a Carrier's coefficient c (0 < c ≤ 1). The results show that, when the accelerating parameter in the range of 0.5 ≤ a ≤ 4, the maximum effective Reynolds number Reeff of the fourth-order five-region solution is both much larger than that of Stokes' and Oseen's ones. For example, when a = 0.5, Reeff = 22.26 is roughly eight times that of Stokes' solution (Reeff = 2.67), and nine times that of Oseen's solution (Reeff = 2.41). Moreover, when the instantaneous Reynolds number Re(t) is smaller than the Reeff, the flow separation angle and the wake length are both consistent with the numerical results obtained by accurately solving the full Navier-Stokes equations. In addition, the flow properties, including the drag coefficients, streamline patterns, and the pressure coefficients, as well as the vorticity distributions also agree well with the numerical results. This study represents a significant extension of our previous study for unsteady Stokes' equation [Xu et al., Phys. Fluids 35, 033608 (2023)] to unsteady Oseen's equation and its generalization.

Electro-fluid-dynamics (EFD) of soft-bodied organisms swimming through mucus having dilatant, viscous, and pseudo-plastic properties

The sperm propelling mechanism has been proposed as a possible resource for soft micro-robots in confined spaces, with potential applications in biomedical engineering. Human sperm cells essentially swim through the non-Newtonian liquid (cervical mucus) to reach their target. Thus, sperm cells swimming through non-Newtonian fluids is not vital only for physiology, but also for the fabrication of swimming micro-robots. Inspired by these remarkable applications, we examine the basic mechanics of spermatozoa motility using an undulating sheet model. This undulating sheet is bounded between two rigid walls which is self-propeling in the negative axial direction. The liquid around the spermatozoa is taken as Carreau fluid with electro-osmotic properties. The application of the lubrication approximation results in the reduction of momentum equations. The resulting ODE is solved numerically via the finite difference method and MATLAB’s built-in routine bvp5c. The unknowns that are present in the boundary conditions are refined by the root-finding algorithm. Power losses, cell speed, flow rate, velocity of the fluid, and streamline pattern are visualized by graphs. The findings of this study have important implications for the designing and optimization of electrically controlled microswimmers.

Unsteady, two-dimensional magnetohydrodynamic (MHD) analysis of Casson fluid flow in a porous cavity with heated cylindrical obstacles

This research presents an analysis of entropy generation during natural convection in a porous medium using triangular heated cylindrical obstacles with equal spacing. The study consists of three cylindrical obstacles arranged in a triangular pattern. Each cylinder is uniformly spaced from its neighboring cylinders, creating equilateral triangles throughout the arrangement. All of these cylindrical obstacles are heated. The triangular arrangement guarantees an even distribution of obstacles across the experimental space. The governing equations, with entropy, are numerically solved using the finite element method. The study aims to investigate the interactions between several key elements in fluid dynamics: Casson fluid, magnetohydrodynamics, the Darcy–Forchheimer model, entropy, and natural convection. The goal is to gain insights into the individual behaviors of these elements and their interactions in combined systems. The results indicate that the Casson fluid parameter has an impact on the flow and heat transfer characteristics, while the Hartmann and Nusselt numbers exhibit control mechanisms for the intensity of natural convection and affect the patterns of isotherms, streamlines, and entropy.

Slip topology of steady flows around a critical point: Taking the linear velocity field as an example

The flow of viscous fluids is considered as the aggregation of the motion of fluid particles when the fluid is conceived to be made up by an infinite number of particles. As an alternative of this conventional model, fluid motion could be understood as the slip of fluid layers with a molecular scale over each other, where the slip structures of fluid and their associated small-scale motion are characterized by an axial-vector-valued differential 1-form, called the vortex field. In this paper, in the case of steady flows we define the swirling degree of the velocity field at a point, and further the swirl field of the steady flow, to study the slip topology of fluid or the local streamline pattern around the critical point. The linear velocity field in the right real Schur form is used to carry out detailed analyses around the isolated critical point. Theoretical deduction and numerical test unveil the connection between the swirling degree and the swirl field, greatly make clear the topological property of slip structures of fluid in steady flows, especially in three-dimensional space.

Instability of Jeffrey Fluid Throughflow in a Porous Layer Induced by Heat Source and Soret Effect

Abstract In this study, we investigated the instability of thermosolutal convection of Jeffrey fluid in a porous layer with internal heating and the Soret effect. The layer is bounded by two fixed permeable parallel plates which are assumed to be isothermal and isosolutal. An existing initial flow in the vertical direction is passing the layer at a constant speed. The flow fields are adequately presented by PDEs and transformed into dimensionless forms. A small perturbation to the basic flow profiles with linear stability analysis results the problem in an eigenvalue problem. The Runge-Kutta method is used to derive the numerical value of the critical thermal Rayleigh number. The convective instability for asymptotic cases for Le = 1 and Pe = 0 are also examined as special cases. The analysis reveals that for a non-positive Soret parameter, the flow is stable for all Lewis numbers and independent of the heat source. But with a positive Soret parameter in the absence of a heat source, the fluid flow is stable for Le = 3 while the influence of a heat source destabilizes the flow for Le > 2. In high and low shear flows with increasing solutal gradient, the solutal Rayleigh number shows a highly destabilizing nature for all Le. Moreover, smaller relaxation and higher retardation time are the most unstable characteristics of the heat source system. In convective longitudinal rolls, the uni-cellular streamline patterns tend to become bi-cellular by the influence of positive Soret parameters and energy sources.

Catalytic effects on peristaltic flow of Jeffrey fluid through a flexible porous duct under oblique magnetic field: Application in biomimetic pumps for hazardous materials

Homogenous and heterogeneous reactions play an essential role in polymer production, combustion, ceramic production, catalysis, distillation, and biochemical procedures. As a result of this advancement, a mathematical model is developed to examine the role of catalytic chemical reaction effects on the magneto-hydrodynamic peristaltic transport in a flexible divergent duct containing a non-deformable porous medium as a model for complex hazardous waste bio-inspired pumping mechanisms. The Jeffrey model is utilized to simulate strong non-Newtonian characteristics. Additional multi-physical features included in the model are heat generation, thermal radiation, Hall current, and complaint wall properties along with an inclined (oblique) magnetic field. The long wavelength and low Reynolds number approximations are deployed to transform the primitive conservation equations from a moving boundary problem to a fixed frame. Appropriate transformations are then utilized to render the model dimensionless. The exact solutions are obtained for stream function and velocity. Further, the R-K-Fehlberg integration scheme is applied to solve the energy and concentration equations. Velocity, temperature, concentration, skin friction, and Nusselt number profiles are visualized graphically. Streamline patterns are also included to capture bolus dynamics. Validation with previous simpler studies has been included. A detailed appraisal of key control parameters on transport characteristics is conducted. It is found that velocity is suppressed with elevation in the damping force parameter while it is enhanced with an increment in regime permeability i. e. Darcy number. Both homogeneous and heterogeneous reactions are observed to exert a significant impact on the species concentration. The volume of the trapped fluid bolus size is shown to be an increasing function of the peristaltic wave amplitude ratio. The present work generalizes existing studies to consider catalytic effects on dissipative peristaltic pumping of the Jeffrey fluid with heat generation and radiative flux, aspects which have been neglected in a single model previously. The simulations are relevant to better characterize the complex transport phenomena in nuclear reactor waste transport via biologically inspired pumping designs.