Vortex Flow Pattern Research Articles

Gas dynamic-thermal-concentration fields and evaporation process of quartz particles in Ar–H2 inductively coupled plasma

The gas dynamic-thermal-concentration fields and evaporation process of quartz particles in the TICP torch of argon–hydrogen plasma have been studied. The effects of different methods of supplying hydrogen on the hydrogen concentration and gas temperature distributions, as well as on the vortex flow patterns have been discussed. The particle injection conditions in the pure argon and argon–hydrogen plasma have been determined. The dependences of the axial gas temperature and velocity distributions on the hydrogen volume fraction, flow rate of central gas and particle feed rate have been established. The effect of hydrogen volume fraction and different methods of supplying hydrogen on the evaporation degree of quartz particle in the TICP torch has been determined. The influences of the particle injection conditions (flow rate of central gas, probe tip position and injection patterns) on the evaporation degree in the TICP torch have also been evaluated. The specific heat cost for quartz particle evaporation has been calculated to evaluate the utilization efficiency of thermal energy.

Influences of mitral annuloplasty on left ventricular flow dynamics assessed with 3-dimensional cine phase-contrast flow magnetic resonance imaging

ObjectivesWe assessed the influence of annuloplasty procedures in mitral repair on left ventricular (LV) vortex flow patterns and aortic outflow patterns, and flow energy loss (EL). MethodsTwenty healthy volunteers and 14 patients who had undergone mitral valve repair were examined using 3-dimensional cine phase-contrast magnetic resonance imaging. A band group included 7 patients with semi-rigid and 2 with flexible partial bands. The ring group included 5 patients with semi-rigid complete rings. LV vortex flow patterns, aortic outflow patterns, EL, and aortic annulus changes during one cardiac cycle were evaluated. ResultsMitral repair induced different vortex flow patterns compared with that of healthy volunteers. The vortex beneath the anterior mitral leaflet with semi-rigid devices was double-stranded in early diastole, and it was single-stranded with flexible bands with a large shift toward the apex during diastole. LVEL in patients who underwent mitral repair (0.84 ± 0.42 mW) was greater than that in healthy volunteers (0.47 ± 0.10 mW). Complete rings disturbed aortic outflow patterns, with EL distribution changes. Smaller devices relative to patient body size disturbed LV flow patterns and caused high EL. No significant relationship was found between indexed ring orifice area and transmitral mean pressure gradient (r = −0.25, P = .414), but a negative relationship exists between indexed ring orifice area and LVEL (r = −0.84, P < .001). ConclusionsMitral repair, especially with relatively small annuloplasty rings, induced abnormal LV flow patterns and EL elevation, which have the potential to be a novel hemodynamic evaluation method after mitral repair.

Experimental Vortex Flow Patterns in the Primary and Secondary Pump Intakes of a Model Underground Pumping Station

In order to provide specific references and suggestions for the design and operation of underground pumping stations, in this paper, an experimental model of an underground pumping station, including 4 pumps and 2 pump intakes (primary and secondary), was obtained through similitude of fluid mechanics. The phase diagrams of various vortices, in terms of different dimensionless numbers are presented, which can reveal their appearance and evolution process. Three specific cases with different vortex flows were analyzed. The experiment results may provide a reference for the current design guidelines for underground pumping stations.

Investigation of vortex flow patterns at the meniscus in a water caster mould

ABSTRACTVortices at the meniscus of the continuous casting mould can entrain mould powder into the liquid pool. The entrained globules will form slivers in the subsequent downstream processing of the slabs. This article presents a three-dimensional computational study of the vortexing at the meniscus with an emphasis on capturing flow behaviours of vortices in continuous casting mould. We have used ANSYS FLUENT 19.2 a commercial CFD package. Two turbulence models, namely standard k- model and shear stress transport (SST) k- model, are employed in this work. The performance of the two turbulence models has been evaluated by comparing the flow measurements from 0.4-scale water model experiments. Both the turbulence models could capture vortices at the top surface. The transient vortex flow characteristics such as formation, expansion (and sustenance), thinning, merging and dissipation of the rotational flow are also predicted by the numerical simulations. In general, the standard k- model and the SST k- model exhibited good capability in predicting the complex, unsteady and turbulent vortex flow phenomena at the meniscus in continuous casting mould.

A case study on internal flow patterns of the two-phase closed thermosyphon (TPCT)

This study investigates types of two-phase flow patterns that affect the heat transfer rate which occurs within the two - phase closed thermosyphon (TPCT) made of heat-resistant glass tube with inner diameters of 7 and 25.2 mm. Aspect ratio was 5 while the inclination angels were 0°, 80° and 90°, and the evaporator temperature were 50, 70 and 90 °C. Furthermore, the addition rate of chemical reactants was 50% by volume of the evaporator component whilst the water temperature within the condensation unit was maintained at 20 °C. From the experimental results, the TPCT's inner diameter was 7 mm, the inclination angels were at 80° and 90°. There were four types of flow pattern including; bubble flow pattern, slug flow pattern, churn flow pattern and annular flow pattern. Churn flow pattern and the annular flow pattern affected the heat transfer rate of the TPCT with the inner diameter of 7 mm at the inclination angels of 80 and 90° respectively. As for the TPCT test, the inner diameter of 25.2 mm with the inclination angels of 80° resulted in four types of the flow patterns, including the bubble flow pattern, slug flow pattern, churn flow pattern and stratified flow pattern respectively. According to the results, churn and stratified flow patterns, were the types of flow that affected the heat transfer rate. According to the experiment of TPCT with inner diameter of 25.2 mm at the inclination angels of 90°, four flow patterns including the bubble pattern, slug flow pattern, churn flow pattern and the vortex flow pattern were found. The vertex flow pattern was initiated when the temperature of the evaporator section was raised from 70 to 90 °C. According to this experiment, the churn flow and the vortex flow patterns were able to affect the heat transfer rates. Furthermore, the experiment revealed that heat flux that was obtained from the experiments of TPCT with the inner diameter of 7 and 25.2 mm showed the highest heat transfer rate at evaporation temperature of 90 °C and the inclination angels of 80° which were 31.88 and 58.15 W, respectively.

Numerical Simulation of the Evaporation Process of Monodispersed Quartz Particles in an Argon Plasma Flow of Induction Plasmatron

The processes of the heating and evaporation of quartz particles in an argon plasma flow of high-frequency induction plasmatron are numerically simulated within the model of a two-phase, collisionless, monodispersed mixture. The conditions for the implementation of a ring-type vortex flow pattern with full and partial particle penetration into the high-temperature zone are determined. The effect of particle feed rate on the gasdynamics of a dispersed flow is shown. The dependences of the evaporation efficiency on the main operating parameters of particle processing process, primarily, the particle feed rate, Joule power of the plasmatron, particle size and injection angle are established. Recommendations are given for the selection of the optimal operating parameters of the plasmatron and flow parameters of the processed quartz particles. It is shown that such a plasmatron with a power of about 5 kW provides a complete evaporation of quartz particle flow with diameter up to 50–70 μm and feed rate up to (8–10) × 10–5 kg/s at specific energy costs at a level of 50 MJ/kg.

Flow around the wing models with straight and swept leading edge in case of contact with turbulent wake

The paper presents the results of experimental studies of the flow around wing models with a straight and swept leading edge in contact with a turbulent wake. The experiments were carried out in subsonic wind tunnels at low Reynolds numbers. A fluffy thread was used to simulate a turbulent wake in the flow. The flow patterns on the surface of the wings were obtained before and after the impact of the turbulent wake at various angles of attack, wing sweep angles and free-stream velocity values. It was found that the wake has a significant effect on flow separation and on vortex structures arising above the wings. The evolution of the vortex flow patterns in the areas of separation of the boundary layer and with a change in the flow regime is shown.

Numerical analysis of the groove effect on the tip leakage vortex cavitating flow

In this paper, the groove effect on the tip leakage vortex cavitating flow characteristics of a simplified NACA0009 hydrofoil with tip gap is studied. Considering local rotation characteristics and curvature effects of the tip leakage vortex flow, the rotation-curvature corrected shear-stress-transport turbulence model is applied to simulate the time-averaged turbulent flow. The Zwart–Gerber–Belamri cavitation model is used to simulate the cavitating flow. The results show that the groove could affect the tip leakage vortex cavitating flow. The groove enhances the interaction between the tip leakage flow and main flow, and then it affects the cavitation of the tip leakage vortex. Compared with the non-groove case, for groove cases of αgre ≤75°, the tip leakage vortex cavitating flow is suppressed, the flow pattern in the gap is improved, and the mean leakage velocity Vlk &lt; 0.8. The region of high leakage velocity is eliminated and the distribution of the pressure is more uniform. The tip leakage vortex cavitation area is reduced, and the maximum decrease is 72.90%. While for groove cases of αgre≥90°, neither the tip leakage vortex cavitating flow nor flow pattern in the tip gap is ameliorated, the mean leakage velocity Vlk lies the range from 0.90 to 0.96. The region of high leakage velocity still exists and even the tip leakage vortex cavitation area is increased. Based on three-dimensional streamlines and vorticity transport equation, the interaction between the tip leakage flow and main flow leads to the variation of the tip leakage vortex cavitating flow. This paper aims for a useful reference to mitigate the tip leakage vortex cavitation and control the influence of the tip leakage vortex cavitating flow for the hydraulic machinery.

Enhancement of Heat Transfer in Laminar Flows Using a Toroidal Helical Pipe

We examine the effectiveness of forced convective heat transfer in a toroidal helical pipe (THP), as a compact process intensification device for use in heat exchangers. Earlier, we showed that mixing was enhanced significantly in such devices due to a continuously changing curvature along the length of the pipe while retaining its compactness. In this work, we examine six Reynolds numbers ranging from 1 to 200, two Prandtl numbers (1 and 7), and two thermal boundary conditions (fixed temperature and fixed flux). The heat transfer efficiency in THP is quantified mainly by the Nusselt number as a function of the downstream distance, and it is compared with that in straight pipes of identical setup. Thus, enhancement by the geometric factor alone is extracted. We found in THP that the Nusselt number is not monotonic but varies periodically around mean values that can be more than four times higher than straight pipes. The unique coupled-Dean vortex flow pattern, due to the varying curvature of the THP axis,...

Vortex dynamics and flow patterns in a two-dimensional oscillatory lid-driven rectangular cavity

Abstract The vortex dynamics in a two-dimensional oscillatory lid-driven cavity with depth-to-width ratio 1:2 has been investigated, covering a wide range of Reynolds numbers and Stokes numbers where this flow is known to be in the two-dimensional regime. Numerical simulations show that the present flow can be divided into four flow patterns based on the vortex dynamics. The regions of these flow patterns are given in the Stokes number and Reynolds number space. For the flow pattern with lowest Reynolds number, there is no transfer of vortices between two successive oscillation half-cycles while for the three other patterns, vortices are carried over from one oscillation half-cycle to the next. For a given Stokes number, the flow pattern appears sequentially as the Reynolds number increases, showing that the transition between the different flow patterns depends strongly on the Reynolds number. However, if the frequency of oscillation is increased (i.e., the Stokes number is increased) for a given Reynolds number, the extrema of the stream function have less time to grow and the center of the primary vortex has less time to move away from the lid. To compensate these effects, the amplitude has to be increased with increasing frequency to maintain the same flow pattern.

Studies of vortex characteristics and gas-dynamic fields in Ar-H2 inductively coupled plasma

Numerical simulation of a technical RF inductively coupled torch of Ar-H2 plasma were made with five turns and under a variation of H2 mole fraction from 0 to 20%. The coupled power and generator frequency varied in the range from 4 to 16 kW and from 1 to 10 MHz, respectively. The gas dynamic fields were compared with experimental and numerical results. The presence of frontal and stern vortices on the upstream and downstream sides of discharge zone was analysed. The differences in the vortex flow patterns and gas-dynamic fields under different H2 mole fractions, coupled powers and generator frequencies were compared. Special attention was paid to investigate the transition conditions of the frontal vortex from Benard to toroidal, as well as the conditions to sweep away the stern vortex. Two different methods have been applied to penetrate the frontal vortex. The critical flow rates of central and outer gases have been determined under different H2 mole fractions, coupled powers and generator frequencies. The choice about the injection probe position to penetrate the frontal vortex in Ar-H2 plasma with different gas compositions has been discussed. The dependences of the vortex intensity on the generator frequency and H2 mole fraction under different coupled powers have been established.

Energy Dissipation in Resynchronization Therapy: Impact of Atrioventricular Delay

Optimal atrioventricular delay (AVD) achieves maximum cardiac output in patients undergoing cardiac resynchronization therapy (CRT). Nonoptimal AVD decreases left ventricular (LV) end-diastolic volume and causes loss of flow momentum prior to LV ejection. We investigated the potential role of energy dissipation (ED) in these changes in cardiac output through the study of intraventricular flow. We hypothesized that short and long AVD increases ED when compared with optimal AVD by altering the physiologic flow mechanics that preserve kinetic energy in the LV. Forty-four patients under CRT underwent echocardiographic LV flow analysis under optimal, short, and long AVD. LV ED and vortical flow in the inflow-outflow tract were studied during the end-diastolic and early systolic period, and paired comparisons were obtained between optimal and nonoptimal values. ED in the left ventricle was minimal in optimal AVD and significantly increased with nonoptimal values (79.1±27.5J/m·sec inoptimal AVD vs 96.5±34.7J/m·sec in short AVD; n=18, P=.006; 123.3±67.6J/m·sec in optimal AVD vs 292.4±202.5J/m·sec in long AVD; P<.001). Increase in ED occurred due to inadequate flow redirection toward the outflow tract in short AVD and due to both turbulence and prolonged ineffective flow rotation in long AVD. Optimal AVD in resynchronization therapy favors physiological vortex flow patterns in the left ventricle during the end-diastolic and early systolic period. These patterns are altered when nonoptimal values are programmed, increasing ED.

Flow Structure and Thrust Change at Gas Jet Injection into the Supersonic Part of a Nozzle

The numerical simulation of gas-dynamic processes accompanying the transverse injection of a gas jet into the supersonic part of a nozzle is considered in the context of creating steering forces in rocket engines. Numerical calculations are conducted based on various turbulence models at different mass flow rates of the injected gas. The calculation results obtained for the non-viscous, laminar, and turbulent formulation of the problem are compared with each other and with the physical experiment data. The formation of a shock wave and vortex flow pattern is discussed. Conclusions about the effect of problem input parameters on the thrust gain coefficient are made.

Структура течения и изменение тяги при вдуве струи газа в сверхзвуковую часть сопла

AbstractThe numerical simulation of gas-dynamic processes accompanying the transverse injection of a gas jet into the supersonic part of a nozzle is considered in the context of creating steering forces in rocket engines. Numerical calculations are conducted based on various turbulence models at different mass flow rates of the injected gas. The calculation results obtained for the non-viscous, laminar, and turbulent formulation of the problem are compared with each other and with the physical experiment data. The formation of a shock wave and vortex flow pattern is discussed. Conclusions about the effect of problem input parameters on the thrust gain coefficient are made.

A Change in the Structure of a Flow under the Action of Highly Inertial Particle when a Hypersonic Heterogeneous Flow Passes over a Body

The results of numerical modeling of the gasdynamic interaction between a highly inertial particle and the shock layer are presented. The evolution of the shock-wave and vortex flow pattern that appears when a particle reflected from a streamlined surface passes through a shock wave is analyzed. It is shown that an essential part is played in the formation of a wave flow pattern by a toroidal vortex, which results in the “nonviscous” detachment of the near-axis incident flow from the symmetry axis and its further interaction with the outer flow and the body surface. It is indicated that an intensive pressure wave passes along the streamlined surface, thus creating the conditions for the intensification of convective heat transfer.

On the Structure and Intensity of Vortex in RF Inductively Coupled Argon Plasma

Numerical simulation of a specific technical RF inductively coupled argon plasma with three coils, discharge current in the range of Jcoil = 100–250 A, and generator frequency 3 MHz is presented. The temperature, pressure, and velocity fields are obtained under different discharge currents and different flow rates of central gas. A reversed flow (vortex) is found between the injected cool gas and high-temperature plasma-forming gas. The formation mechanisms of such a vortex and the influence of the discharge current and flow rate of central gas on the vortex structure and intensity are studied. Special attention is paid to investigating two different kinds of vortex flow patterns—Benard and toroidal. A critical flow rate of central gas above which the flow pattern would transform from Benard to toroidal is determined and approximated as a function of the discharge current by theoretical calculations and numerical simulations. The maximum negative velocities along the axis in the vortex zone are also determined under different discharge currents and different flow rates of central gas.

Numerical investigation into the characteristics of a vortex in an argon inductively coupled plasma

A numerical simulation of a technical radio frequency inductively coupled plasma was made with three coils and coupled power in the range of 2–10 kW. The generator frequency varied from 1.76 to 13.56 MHz. The mechanisms of forming a vortex on the upstream side of the discharge and the influences of coupled power, generator frequency and flow rate of central gas on the vortex dimensions were studied. Special attention was paid to investigate two different kinds of vortex flow pattern—Benard and toroidal—as well as the vortex intensity under those two kinds of flow pattern. A critical flow rate of central gas, above which the flow pattern would transform from a Benard to a toroidal vortex, was found on the basis of force balance between the dynamic head of central cool gas and magneto-hydrodynamic and Stokes drag forces of plasma. The influences of coupled power, generator frequency, diameter of the injection probe and the compositions of central gas on the critical flow rate of the central gas were discussed. The dependences of the vortex intensity and maximum vorticity on the coupled power under different generator frequencies and flow rates of central gas were established.

A High-Throughput Electrokinetic Micromixer via AC Field-Effect Nonlinear Electroosmosis Control in 3D Electrode Configurations.

In this study, we make use of the AC field-effect flow control on induced-charge electroosmosis (ICEO), to develop an electrokinetic micromixer with 3D electrode layouts, greatly enhancing the device performance compared to its 2D counterpart of coplanar metal strips. A biased AC voltage wave applied to the central gate terminal, i.e., AC field-effect control, endows flow field-effect-transistor of ICEO the capability to produce arbitrary symmetry breaking in the transverse electrokinetic vortex flow pattern, which makes it fascinating for microfluidic mixing. Using the Debye-Huckel approximation, a mathematical model is established to test the feasibility of the new device design in stirring nanoparticle samples carried by co-flowing laminar streams. The effect of various experimental parameters on constructing a viable micromixer is investigated, and an integrated microdevice with a series of gate electrode bars disposed along the centerline of the channel bottom surface is proposed for realizing high-flux mixing. Our physical demonstration on field-effect nonlinear electroosmosis control in 3D electrode configurations provides useful guidelines for electroconvective manipulation of nanoscale objects in modern microfluidic systems.

A topology-alterative two-phase flow solver and its validation for a dynamic hydraulic discharge process

ABSTRACTIn this paper, a domain-topology-based, two-phase, incompressible flow model is proposed to simulate transient flow variations associated with the gate opening motions of water conservancy projects, such as hydropower stations with plain and radial gates. The research source code is written in the OpenFOAM platform and incorporates the interDyMFoam solver. Two benchmark experiments were performed in the laboratory to validate the numerical results. The water level, pressure, flow pattern and development of vortices were recorded for comparison with numerical solutions. The results show that the relative error associated with the weir flow time was less than 5.00%. Moreover, good agreement was obtained between the time history curves of the free surface elevation and pressure based on numerical and experiment results. The detailed flow pattern reflects the simulation capability of the model, which can be used to numerically investigate the generation mechanisms of vertical vortices around gate grooves. The proposed model can be applied to further investigate flow variations in real hydraulic engineering applications.

Characteristics of Thermal–Hydraulic and Heat Transfer in Liquid Windowless Target of Accelerator Driven Subcritical

In recent years, the morphological characteristics and stabilization methods of free interface in liquid windowless target become hot research topics in accelerator driven subcritical system (ADS). Based on the structure design of a certain windowless spallation target, computational fluid dynamics (CFD) software of CFX was used to simulate and analyze its free interface character. The method of k–ε turbulence, cavitation, and volume of fluid (VOF) model was used to study the flow characteristic of liquid Lead-Bismuth eutectic (LBE) alloy with cavitation phase change and to analyze the free interface morphology characteristics of coolant in the target area. It is concluded that the target region forms two stable free interfaces when fluid outlet pressure is in the range of 10–40 kPa and fluid entrance velocity is in the range of 0.5–1.2 m/s. The flow field near the free interface structure is complex. The vortex region appears, and the disorders in the vortex flow pattern lead to fluctuation of the free interface. After the study of stable free interface morphology establishing process, heat transfer characteristic of windowless target was further analyzed.