Streamline Flow Research Articles

In-situ flow visualization with Geo-Positron-Emission-Tomography in a granite fracture from Soultz-sous-Forêts, France

We investigate the fluid flow field in a fractured granite core sample. Sequential imaging with Positron-Emission-Tomography (PET) allows direct reconstruction of flow streamlines, thus providing a unique insight into the fluid dynamics of complex fractured crystalline materials. Pulse migration experiments using the positron-emitting radionuclide 18F− as tracer were conducted on a fractured granitic drill core, originating from a depth of 1958 m of the Enhanced Geothermal System (EGS) reference site at Soultz-sous-Forêts, France. The flow field was analyzed as a function of in- and outlet positions across the fracture, as well as applied flow rates. Different flow path characteristics were identified. Both the fracture aperture variation and the topography of the fracture surface affect the flow field with consequences on flow channeling and preferential flow paths. Furthermore, pulse migration experiments were also numerically simulated with a 2.5D model using COMSOL Multiphysics®.While the higher flow rate experiments show wider and higher dispersion of the flow path, lower velocity results in more localized flow and channeling behavior. This type of study thus yields enhanced experimental insights into the hydrodynamics of fracture flow and its relation to the rough structure of a single fracture, compared to input-output experiments. It can help to validate model simulations and experimentally determine hydrodynamic parameters needed for reactive transport modeling that are otherwise estimated with a high degree of uncertainty.

Computational analysis of conductive fluid flow with tangential components of magnetic flux density and electric field in metallic and non-metallic circular pipe

This paper has focused on the study of flow characteristics of a steady conductive fluid through a circular pipe in the presence of an applied transverse uniform magnetic field. A numerical simulation of the fluid flow was performed using a multi-physics computational tool. The radial velocity distribution due to the effect of the tangential component of induced magnetic flux density and electric fields at various axial positions is examined in metallic and non-metallic surfaces of the circular pipe. This simulation study helps to analyse the effect of drag force on the variation in axial velocity close to the metallic and non-metallic walls. The induced electric potential is directed along the normal to the Laplacian tangential surface of the pipe. In addition to that, sigmoidal-shaped field profiles are observed when the fluid flow crosses from the upstream to downstream of the magnet edge and vice versa along the axial length of the circular pipe. Simultaneously, it is observed that the average velocity of the fluid flow decreases for a laminar and increases for turbulent Reynolds number. Streamline plots pertinent flow variable such as flow velocity are presented for non-conducting and conducting walls.

Lagrangian transport in the time-periodic two-dimensional lid-driven square cavity

The Lagrangian transport in the laminar incompressible flow in a two-dimensional square cavity driven by a harmonic tangential oscillation of the lid is investigated numerically for a wide range of Reynolds and Strouhal numbers. The topology of fluid trajectories is analyzed by stroboscopic projections revealing the co-existence of chaotic trajectories and regular Kolmogorov–Arnold–Moser (KAM) tori. The pathline structure strongly depends on the Reynolds number and the oscillation frequency of the lid. Typically, most pathlines are chaotic when the oscillation frequency is small, with few KAM tori being strongly stretched along instantaneous streamlines of the flow. As the frequency is increased, the fluid motion becomes more regular and the size of the KAM tori grows until, at high frequencies, they resemble streamlines of a mean flow.

Lifting Stokes' paradox by accelerating flow past a circular cylinder and extension of the analysis to the sphere

It is known that Stokes' paradox exhibits in various flow conditions, most notably, in flow past a two-dimensional (2D) circular cylinder. In this study, we provide an example through detailed analytical solution that Stokes' paradox can be lifted by accelerating flow past a stationary cylinder. The analysis is also extended to the case of the accelerating flow past a stationary sphere although in this case, there is no Stokes' paradox. The effects of the acceleration parameter on the flow streamlines, the pressure, and the vorticity distributions, as well as on the drag coefficient, are investigated. The drag comprises the potential component and vorticity component, which are further due to form drag and frictional drag receiving a separate investigation. However, the drag decomposition is also examined the viewpoint of the force decomposition: the total drag = the potential component + surface vorticity component + volume vorticity component.

Influence of inflow directions and setting angle of inlet guide vane on hydraulic performance of an axial-flow pump

Inlet flow direction significantly affects the hydraulic performance of an axial-flow pump. Usually, the research papers ignore this phenomenon, resulting in discrepancies between simulation and experimental results. This study examines the influence of inflow direction in five cases (0%, 5%, 10%, 15%, and 30% pre-swirl intensities) to determine the relationship between the pre-swirl intensity and the hydraulic performance of the axial-flow pump. Based on this, changing the setting angle of the inlet guide vane (IGV) is proposed and thoroughly investigated to reduce the effect of inflow direction. In this study, the influence of clearances in IGV blades on hydraulic performance is also investigated in detail. Numerical simulations are performed using ANSYS–CFX and a shear stress transport reattachment modification (SST k-omega) turbulence model with small y+ values at all walls. Specifically, the hydraulic performance curves and internal flow characteristics, including contours and streamlines, are assessed and analyzed. The inflow direction significantly impacts the hydraulic efficiency of the axial-flow pump. Increased pre-swirl intensity causes more loss in the IGV passage. The internal flow field and performance are not affected by the clearance at the hub and shroud of the IGV. However, the tip clearance of the impeller causes a decrease in hydraulic efficiency due to the tip leakage vortex. By adjusting the setting angle of the IGV, the efficiency and head gradually increase from a negative to a positive setting angle. Additionally, 30° is considered the critical setting angle for IGV.

Unsteady convective ferrohydrodynamic flow of MnZnFe2O4/FeCrNbB - EG hybrid nanofluid in a horizontal channel with porous fins and semi-circular heaters

In this study, we investigate the unsteady incompressible flow of ethylene-glycol (EG) based MnZnFe2O4/ FeCrNbB hybrid nanofluid through a horizontal channel. Three semi-circular heaters are mounted on the lower channel wall, whereas four porous fins are mounted on the upper channel wall. The Forchheimer model is utilized to describe convective nanofluid flow within the porous fins. Also, a variable magnetic field is produced by an electrical wire within each heater and induces motion and heat transfer within the hybrid nanofluid. Governing equations associated with the mathematical model are numerically solved via the mixed finite element technique. Using the computed graphical and tabular results, we examine the effects of the magnetic parameter (105≤Mn≤3×106), size of the porous fins (0.2≤hfin≤0.6), heater radius (0.2≤r0≤0.3), and solid volume fractions of MnZnFe2O4 and FeCrNbB nanoparticles (0≤ϕ1≤0.02 and 0≤ϕ2≤0.02) on the flow velocity, streamlines, isotherms, pressure drop, and heat transfer performance in the channel. The main findings of the study are that increasing the magnetic number and volume fractions of MnZnFe2O4 and FeCrNbB nanoparticles, and decreasing the height of the porous fins and size of the heaters, leads to greater convective heat transfer in the channel. Furthermore, the pressure drop is enhanced when each of the aforementioned parameters is increased.

The rangeomorph Pectinifrons abyssalis: Hydrodynamic function at the dawn of animal life

Rangeomorphs are among the oldest putative eumetazoans known from the fossil record. Establishing how they fed is thus key to understanding the structure and function of the earliest animal ecosystems. Here, we use computational fluid dynamics to test hypothesized feeding modes for the fence-like rangeomorph Pectinifrons abyssalis, comparing this to the morphologically similar extant carnivorous sponge Chondrocladia lyra. Our results reveal complex patterns of flow around P.abyssalis unlike those previously reconstructed for any other Ediacaran taxon. Comparisons with C. lyra reveal substantial differences between the two organisms, suggesting they converged on a similar fence-like morphology for different functions. We argue that the flow patterns recovered for P.abyssalis do not support either a suspension feeding or osmotrophic feeding habit. Instead, our results indicate that rangeomorph fronds may represent organs adapted for gas exchange. If correct, this interpretation could require a dramatic reinterpretation of the oldest macroscopic animals.

Effects of Boulder Arrangement on Flow Resistance Due to Macro-Scale Bed Roughness

Flow resistance in gravel-bed channels is not only affected by the shape and size of the roughness elements, but also by their arrangement on the channel bed surface (position to flow streamlines, spacing between elements, and their protrusion from the channel bed). Many investigations proved that open channel flow resistance can be obtained by integrating the power velocity profile. For a macro-scale roughness condition, this study aims to investigate the effect of different boulder arrangements on flow resistance. First, for each arrangement, the equation relating Γ function of the power velocity profile, the Froude number, and the channel slope was calibrated using available measurements performed in a flume covered by pebbles with “Random”, “Transversal stripe”, and “Longitudinal stripe” arrangements. For each arrangement, the experimental datasets were divided to consider the effects of boulder concentration Ch. Moreover, the relationship obtained for the “Random” arrangement and element concentration lower than 48% was tested using literature measurements performed in a flume covered by coarse elements randomly arranged. Finally, the effects of the different boulder arrangements on the flow resistance law were investigated by imposing a concentration threshold. The results demonstrated that (i) the Darcy–Weisbach friction factor can be accurately estimated by the proposed flow resistance equation, (ii) the flow resistance increases with Ch for low values (<48%) of concentration, while it does not depend on Ch for high concentrations (≥48%), and (iii) the effect of the boulder arrangement on flow resistance law is more evident for low element concentrations.

Direct Carotid Artery Cutdown and flow diversions for the bilateral Internal Carotid Artery Dissecting Pseudoaneurysms: A Case Report

Background: Surpass streamline flow diversion is performed by transfemoral, transradial or both approaches. Safety and feasibility of direct carotid artery cutdown and is not known. Objective is to report Surpass streamline flow diversion via direct carotid artery utdown for a patient with bilateral internal carotid artery dissecting pseudoaneurysm. Method: Case report. Outcome was measured using modified ranking scale (mRS). Results: Sixty-seven-year-old man with history of repaired aortic arch dissecting aneurysm using aortic stent, developed worsening headaches and dizziness and diagnosed with bilateral internal carotid artery dissecting pseudoaneurysm on a computed tomographic angiography; right internal carotid artery dissecting pseudoaneurysm measured 19x15x20 mm and left was 16x9x22 mm. Digital subtraction angiogram was attempted but failed. A direct carotid artery cutdown followed by surpass streamline flow diversion was performed in a staged fashion. A 6-french sheath was placed from right common carotid artery to right internal carotid artery by a vascular surgeon and was confined with digital subtraction angiography. An intermediate catheter was navigated to the internal carotid artery beyond the internal carotid artery dissecting pseudoaneurysm and surpass streamline flow diversion was achieved with 3 devices; 4x50 mm x2 and 5x40 mm. Carotid artery cutdown site was sutured by vascular surgeon. Patient was extubated and discharged home in 48 hours with NIHSS 0 and mRS1 at his baseline. The left internal carotid artery dissecting pseudoaneurysm was repaired after 3 month using similar technique as described above with two 5x50 mm flow diverters. For the second procedure, angioplasties were required for better appositions of flow diverters. Patient was discharged home in 24 hours. Patient’s symptoms resolved and resumed baseline activities. Prescribed to continued 325 mg aspirin and 75 mg clopidogrel for six months followed by 162 mg aspirin and 75 mg of clopidogrel. Patient maintained mRS 0 in follow-up visits but refused to have a computed tomographic angiography, which finally performed in 24 months, demonstrates complete obligations of the left internal carotid artery dissecting pseudoaneurysm but occlusion of right internal carotid artery with robust collaterals from left internal carotid artery through collaterals. Patient admits premature discontinuation of antiplatelets when he learned about his computed tomographic angiography results. Conclusion: This is the first report of treatment of bilateral internal carotid artery dissecting pseudoaneurysm repaired by direct carotid artery cutdown approach. This is also the first report of a patient with an aortic arch stent, who developed bilateral internal carotid artery dissecting pseudoaneurysm and direct carotid artery cutdown required for treatment. Additionally, antiplatelets must be continued to prevent device occlusion.

Comparative Study on the Effect of Leading Edge Protuberance of Different Shapes on the Aerodynamic Performance of Two Distinct Airfoils

This study investigated the effect of leading-edge protuberances on the aerodynamic performance of two distinct airfoils with low Reynold’s number (Re): E216 and SG6043. Three protuberance shapes, namely sinusoidal, slot, and triangular, were considered. The amplitudes (A) of protuberances considered were 0.03c, 0.06c, and 0.11c, and the wavelengths (W) were 0.11c, 0.21c, and 0.43c, where c is the chord of the airfoil. The numerical and experimental analyses were performed in the angle of attack (AoA) range of 0° to +20° at and Re of 105. The numerical investigation was performed using the commercial computational fluid dynamics package ANSYS FLUENT. The SST k-ɷ model was used to simulate turbulent flow. The experimental force measurements were conducted using a highly sensitive three-component force balance in a subsonic wind tunnel facility. The flow physics was analyzed using vorticity contours in streamwise and spanwise slices and static pressure distribution contours. The smoke flow visualization technique was used to observe flow streamlines, boundary layer separation, and reattachment over the airfoil surface. The result indicated that the triangular and slot protuberances were the most beneficial for improving poststall lift and reducing skin friction drag. The operating mechanism involved a shift in pressure distribution due to leading-edge alterations and flow energization by secondary flow emanating from the protuberances.

Statistical topology of the streamlines of a two-dimensional flow

Recent experiments on mucociliary clearance, an important defense against airborne pathogens, have raised questions about the topology of two-dimensional (2D) flows, such as the proportion of topologically closed and open streamlines. We introduce a framework for studying ensembles of 2D time-invariant flow fields and estimating the probability for a particle to leave a finite area (to clear out). We establish two upper bounds on this probability by leveraging different insights about the distribution of flow velocities on the closed and open streamlines. We also deduce an exact power-series expression for the trapped area based on the asymptotic dynamics of flow-field trajectories and complement our analytical results with numerical simulations.

Surpass Intracranial Aneurysm Embolization System Pivotal Trial to Treat Large or Giant Wide-Neck Aneurysms – SCENT: 3-year outcomes

BackgroundTo report the 3-year safety and effectiveness of the Surpass Streamline flow diverter in the SCENT trial (Surpass Intracranial Aneurysm Embolization System Pivotal Trial to Treat Large or Giant Wide-Neck...

Reduced surface accumulation of swimming bacteria in viscoelastic polymer fluids

Surface-associated bacterial communities flourish in nature and in the body of animal hosts with abundant macromolecular polymers. It is unclear how the endowed viscoelasticity of polymeric fluids influences bacterial motile behavior in such environments. Here, we combined experiment and theory to study near-surface swimming of flagellated bacteria in viscoelastic polymer fluids. In contrast to the swimming behavior in Newtonian fluids, we discovered that cells swim in less curved trajectories and display reduced near-surface accumulation. Using a theoretical analysis of the non-Newtonian hydrodynamic forces, we demonstrated the existence of a generic lift force acting on a rotating filament near a rigid surface, which arises from the elastic tension generated along curved flow streamlines. This viscoelastic lift force weakens the hydrodynamic interaction between flagellated swimmers and solid surfaces and contributes to a decrease in surface accumulation. Our findings reveal previously unrecognized facets of bacterial transport and surface exploration in polymer-rich environments that are pertinent to diverse microbial processes and may inform the design of artificial microswimmers capable of navigating through complex geometries.

Propagative-rhythmic membrane contraction modulated efficient micropumping of non-Newtonian fluids

We here discuss a novel bioinspired pumping mechanism of non-Newtonian fluids in a microfluidic configuration, consistent with the propagative rhythmic contraction–expansion of a membrane attached to the wall of the fluidic channel. We consider the Rabinowitsch model to represent the rheology of non-Newtonian fluids. By employing lubrication theory and approximating the underlying flow to be in the creeping regime, the transport equations governing the pumping process are framed pertaining to the chosen setup. The transport equations are then evaluated by employing a well-established perturbation technique. By depicting the flow velocity components, streamline patterns, and velocity contours graphically, we aptly discuss the flow structure developed in the flow pathway and demonstrate the eventual consequence of these flow parameters to the net throughput during both compression and expansion phases of the pumping process. Finally, by demonstrating a phase-space diagram, we also discuss the impact of fluid rheology and membrane kinematics on the pumping capacity. The results obtained from the proposed model establish that the net flow owing to propagative rhythmic membrane contraction strongly relies on exponent parameter M and rheological parameter β. These consequences are expected to be of substantial practical relevance in designing micropumps intended to yield unidirectional flow of the complex fluids with improved efficiency, commonly used in biochemical/biomicrofluidic applications.

Experimental and numerical study on the performance of a new dual-inlet gas–liquid cylindrical cyclone (GLCC) based on flow pattern conditioning

Gas-Liquid Cylindrical Cyclone (GLCC) is a compact and efficient separation device used in oil and gas separation field. A new dual-inlet GLCC which can change the flow area ratio was designed and examined. The liquid separation efficiencies under five flow area ratios were experimentally measured. The liquid film velocity distribution was measured by MATLAB PIVlab. The finite volume method (FVM) was used to discretize the control equations. The liquid film thickness, gas–liquid flow distribution ratio and liquid flow streamline were obtained. The simulated liquid film velocities were seen to be consistent with experimental observations. Experimental and simulation results showed that by changing the flow area ratio of the upper and lower inlet pipes, the flow distribution in the upper and lower inlet pipes changed, liquid entering the upper GLCC cylinder reduced, the liquid film tangential velocity near the lower inlet increased and the change of liquid film axial velocity tended to be stable. The new type of GLCC expanded the safe operational separation envelop (envelop of the no LCO).

Preliminary Experience of the Surpass Streamline Flow Diverter for Large and Giant Unruptured Internal Carotid Artery Aneurysms.

As of January 2021, the Surpass Streamline (SS) is the most recently approved flow diverter in Japan. A total of 28 Japanese patients, including 9 clinical trial patients, with 28 large or giant unruptured internal carotid artery (ICA) aneurysms, underwent SS embolization at Juntendo University Hospital. Procedural failure occurred in two patients due to the difficulty to navigate the device in the tortuous parent artery. Therefore, 26 patients with 26 aneurysms were available for clinical and anatomical assessments. Patients' mean age was 62.6 years (range 46-86), and 24 patients (92.3%) were female. Mean aneurysm size and neck width were 15.4 mm and 7.7 mm, respectively, with 20 saccular and 6 fusiform aneurysms. Seven aneurysms were symptomatic due to the aneurysmal mass effect. Twenty patients underwent a 6-month follow-up angiography to evaluate the degree of occlusion. Anatomical outcomes were 12 (60%) complete occlusion (CO), 4 (20%) residual neck (RN), and 4 (20%) residual aneurysm. Favorable aneurysm occlusion consisted of CO, and RN was achieved in 16 (80.0%). There were no significant device stenoses. Aneurysmal mass effect improved in one and was unchanged in eight patients. There were three device-related complications, namely, delayed aneurysm rupture, minor ischemic stroke, and device occlusion (11.5%). One patient with minor ischemic stroke fully recovered before 30 days, and our series showed 7.7% risk of major ipsilateral stroke and neurological death at 30 days. The SS embolization for large and giant unruptured ICA aneurysms offers satisfactory anatomical and clinical outcomes with a low risk of device-related complications.

Numerical analysis of hydrodynamic and thermal characteristics of three inside channel configurations of a plate and shell heat exchanger (PSHE)

The Plate and Shell Heat Exchanger (PSHE) is a variation of the Plate Heat Exchanger (PHE) with a more compact and robust geometry. This paper presents the analysis of the flow in the inner channel formed by a pair of plates of a PSHE employing computational fluid dynamics to determine the hydrodynamic and thermal characteristics for three Chevron angle configurations, 15° × 15° (High/High-HH), 45° × 45° (Low/Low-LL) and 15° × 45° (High/Low-HL). The ANSYS CFX software was employed with the application of the Standard k-ε and the SST (Shear-Stress-Transport) turbulence models for comparison. Experimental pressure drop data and flow streamlines were used to validate the numerical model and to analyze simplifications in the geometric model. Pressure drop, friction factor, and Nusselt number were evaluated for the three geometries studied. A local analysis of the parameters that describe the channels was also performed in this study.

Melting dynamics analysis of a multi-tube latent heat thermal energy storage system: Numerical study

This numerical study investigates the melting dynamics of paraffin wax as a phase change material (PCM) in a multi-tube latent heat thermal energy storage system (MT-LHTESS). The performance of an arrangement with four tubes is compared with a concentric single tube arrangement keeping the same cross-section area of heat transfer fluid tubes and the same PCM quantity. Four longitudinal fins of two types are also incorporated to further improve the melting. Thirteen cases with different arrangements of tubes and fins are compared in this study. The study attempts to select a suitable arrangement of the tubes. A two-dimensional enthalpy-porosity model in ANSYS-Fluent is used to solve the governing equations. The melting results are depicted as the contours of liquid fraction, temperature, and flow streamlines. The transient performance is assessed based on progress plots of liquid fraction and average domain velocity. It is observed that splitting into multiple tubes and using fins enhance the melting performance. The generation and coalescence of small vortices in the molten PCM accelerate the melting performance. The staggered array, larger eccentricity, and (+ type) finned tubes outperform their counterparts. The lowest melting time is observed in Case 2(+), having four staggered tubes, at 30 mm eccentricity, and with (+ type) fins. This case takes 75 min for complete melting, and 1411.1 kJ/m heat at a rate of 322 W/m is stored. The melting time gets reduced by 53.3–71.1% using four tubes and by 65.78–83.33% using finned four tubes as compared to the single tube case.

Plasma Gurney Flap Flight Control at Low Angle of Attack

A flight control concept without movable surfaces using electrofluidic actuators is assessed from low-speed scaled two-dimensional (2-D) rectangular wings up to three-dimensional (3-D) full-scale tapered swept wings at realistic aircraft operating conditions. The plasma Gurney flap concept consists of placing spanwise dielectric barrier discharge (DBD) plasma actuators on both sides of a wing or empennage near the trailing edge, and pointing in opposite directions, to change the flow curvature in this region, thus altering lift. Low-speed wind-tunnel tests and corresponding computational fluid dynamics (CFD) simulations are first carried out for this concept on scaled 2-D rectangular wings. Measured lift moment and flow streamlines are used to validate the simulation (CFD) tool. Simulations with this tool are then performed to assess the effect of wing taper and sweep on the effectiveness of the concept at low speed and to evaluate the concept for full-scale 3-D tapered swept-wing geometries for a single-aisle airliner. The results indicate that the plasma Gurney flap has better performance on tapered and swept wings relative to rectangular wings because of the reduction in the velocity component normal to the plasma actuator. Moreover, the presence of shocks at cruise flight conditions improves the effectiveness of the plasma Gurney flap concept.

Two-Dimensional Turbulent Thermal Free Jet: Conservation Laws, Associated Lie Symmetry and Invariant Solutions

The two-dimensional turbulent thermal free jet is formulated in the boundary layer approximation using the Reynolds averaged momentum balance equation and the averaged energy balance equation. The turbulence is described by Prandtl’s mixing length model for the eddy viscosity νT with mixing length l and eddy thermal conductivity κT with mixing length lθ. Since νT and κT are proportional to the mean velocity gradient the momentum and thermal boundaries of the flow coincide. The conservation laws for the system of two partial differential equations for the stream function of the mean flow and the mean temperature difference are derived using the multiplier method. Two conserved vectors are obtained. The conserved quantities for the mean momentum and mean heat fluxes are derived. The Lie point symmetry associated with the two conserved vectors is derived and used to perform the reduction of the partial differential equations to a system of ordinary differential equations. It is found that the mixing lengths l and lθ are proportional. A turbulent thermal jet with νT≠0 and κT≠0 but vanishing kinematic viscosity ν and thermal conductivity κ is studied. Prandtl’s hypothesis that the mixing length is proportional to the width of the jet is made to complete the system of equations. An analytical solution is derived. The boundary of the jet is determined with the aid of a conserved quantity and found to be finite. Analytical solutions are derived and plotted for the streamlines of the mean flow and the lines of constant mean thermal difference. The solution differs from the analytical solution obtained in the limit ν→0 and κ→0 without making the Prandtl’s hypothesis. For ν≠0 and κ≠0 a numerical solution is derived using a shooting method with the two conserved quantities as targets instead of boundary conditions. The numerical solution is verified by comparing it to the analytical solution when ν→0 and κ→0. Because of the limitations imposed by the accuracy of any numerical method the numerical solution could not reliably determine if the jet is unbounded when ν≠0 and κ≠0 but for large distance from the centre line, ν>νT and κ>κT and the jet behaves increasingly like a laminar jet which is unbounded. The streamlines of the mean flow and the lines of constant mean temperature difference are plotted for ν=0 and κ=0.