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To investigate the gas-liquid two-phase flow characteristics in an emergency rescue drainage pump, the MUSIG model was adopted to analyze the effect of the gas phase on the internal flow characteristics of the pump. The results show that the gas phase predominantly accumulated in the impeller region, with significant tendencies for large diameter bubbles to fragment into smaller diameter bubbles. The bubbles of the impeller blades converged towards the middle zone of the blade near the hub, forming an air pocket that obstructed the flow passage through the impeller. Such findings ultimately resulted in a loss of pump performance. Moreover, as the diameter of inlet bubble increased, there was a greater tendency for the gas phase to converge into a concentration distribution, leading to unfavorable flow conditions in the pump. This phenomenon ultimately led to a decline in pump performance and may have resulted in the loss of water conveyance functionality. Meanwhile, the O method was used to investigate the vortex flow within the drainage pump under different gas contents. As the inlet gas volume fraction increased, the vortex area expanded and the vortex tended to fragment into multiple smaller pieces, resulting in the formation of more complex structures. [ABSTRACT FROM AUTHOR]

In order to determine the most suitable turbulence model for studying the aerodynamic performance of bus, the effects of different turbulence models on the aerodynamic characteristics of bus were investigated. A comparative analysis was conducted on five turbulence models (IDDES, DDES, DES, LES, URANS). The pressure distribution on the cross section at x=0 and y=0 is also analyzed for each model. The results reveal that IDDES accurately captures the negative pressure at the rear of the bus and predicts the pressure gradients more effectively than other models. IDDES also captures more vortices at the head of the bus and predicts the wake flow more widely than other models. DDES has obvious shedding phenomenon in the wake flow, while IDDES provides a relatively smooth airflow trajectory, but its prediction of airflow trajectory at a distance is less clear. Through quantitative and qualitative analyses of the aerodynamic characteristics of bus under different turbulence models, it can be concluded that IDDES is the most suitable turbulence model to study the aerodynamic characteristics of bus. [ABSTRACT FROM AUTHOR]

Under the influence of crosswind, when high-speed trains (HSTs) meet on a bridge, they produce complex vortexes, strong aerodynamic loads, and other aerodynamic effects. The purpose of this paper is to reveal the influences of crosswind and windbreaks on the vortexes generated by HSTs, the pressure distributions on the surfaces of the trains, and the aerodynamic load coefficients of the trains when they meet on a bridge, as well as the influence of the pressure waves generated by the trains on the windbreaks. The three-dimensional incompressible improved delayed detached eddy simulation (IDDES) method based on the SST k-ω turbulence model is used for numerical calculation purposes, and the overset grid method is used to realize the relative motions of the trains. The results show that the windbreaks can reduce the negative pressure (NP) imposed on the train surface and effectively improve the pressure distribution; crosswinds have a significant impact on the vortexes generated by trains, and the vortexes generated by the upstream train affect the stability of the downstream train; windbreaks can reduce the aerodynamic load applied when trains meet and thus improve the safety of the trains; and the head and tail waves generated by trains impose pressure on the windbreaks, which affects the reliability of the windbreaks installations. The simulation results can provide a preliminary reference for future research. [ABSTRACT FROM AUTHOR]

In order to study the unsteady flow and vortex characteristics of tongue cavitation, numerical calculation is carried out for the whole flow channel given different conditions. Then, the calculation results are verified experimentally. The results show that after the occurrence of tongue cavitation in the centrifugal pump, it deteriorates with the decrease of NPSHa. However, when NPSHa is reduced to 3.78 m, it does not change significantly anymore with the decrease of NPSHa. The extrusion of fluid by the vapor at the tongue promotes the formation of the separation vortex, and the re-jet flow caused by the separation vortex leads to vapor shedding. The frequency of cavitation shedding is consistent with the frequency of vortex shedding. In the vorticity transport equation, the relative vortex stretching term and the relative vortex dilatation term dominate the vapor shedding by controlling the change in vorticity. The baroclinic torque term mainly affects the change of vorticity at the vapor-liquid interface, but to a much lesser extent than the first two terms. [ABSTRACT FROM AUTHOR]

In the field of hydrogen safety and combustion, the effect of obstacles on hydrogen deflagration is a topic of general interest to scholars. In previous studies, scholars usually used uniform obstacles under various operating conditions and obtained conclusions by changing their number and positions. However, in practice, the shapes of obstacles at an accident site are often not the same and regular. In this paper, a series of obstacles with variations in length were investigated, and the effects of the obstacles on hydrogen deflagration under different working conditions were analyzed. The configuration of the obstacles with gradually increasing lengths amplified the vortices in the flow field so that the propagation direction of the flame front surface was reversed after passing three obstacles. The variations in the lengths of the obstacles had a significant stretching effect on the propagation of the flame and a considerable acceleration effect on the propagation speed of the flame. The main reason for the acceleration was the rapid propagation of the flame achieved by the vortex when rupture occurred. The change in the pressure gradient that occurred at the center of rotation caused rapid movement of the combustion gases, which ultimately led to an increase in the flame propagation speed. A configuration with gradually increasing lengths of the obstacles promoted the overpressure. A configuration with gradually decreasing lengths of the obstacles suppressed the overpressure. The reason for the formation of the local high-pressure area was that unburned gas was accumulated there by pressure waves and the obstacle walls, and then the thermal expansion formed a high pressure. The Rayleigh-Taylor and Kelvin-Helmholtz instabilities caused the overpressure to rise further. The results can provide a theoretical basis for hydrogen transportation, storage, and safety. [ABSTRACT FROM AUTHOR]

In this study we examine the flow of inelastic fluids with various shear properties in axisymmetric contractions with various contraction ratios are selected as 4:1, 6:1 and 8:1 with both rounded-corner and sharp. Particular attention is paid to the effect of shear thickening and shear thinning upon the solution behavior. Power-law inelastic model is employed coupling with the conservation of momentum equation and continuity equation. The numerical simulation of such fluid is performed by using the Taylor Galerkin pressure correction (T-G/P-C) finite element algorithm. The effects of geometry structure and many factors such as Reynolds number (Re) and the parameters of power law model are presented in this study. Particularly, in this study we are focused on the influence of these factors on the solution components and the level of convergence. This research was a comparative study between sharp and rounded-corner contraction geometries with a ratio of 4:1, and to another comparative study among sharp contraction geometries with ratios of 4:1, 6:1, and 8:1. The practical implications of this study focused on vortex length and the impact of varying the parameters of the power law model and the Reynolds number (Re) on it for 4:1 contraction flow. The study dealt with the effect of different geometries on the rates of convergence of velocity and pressure as well as the characteristics of axial velocity and pressure on the axis of symmetry. [ABSTRACT FROM AUTHOR]

One of the basic phenomena when a liquid leaves a tank is the formation of vortices. This phenomenon can have a significant impact on the liquid mass remaining in the tank and the ingress of air and bubbles into the system. As a result, the performance of the system can be disturbed. The purpose of this study is to numerically investigate the effect of gas pressure on vortex formation and critical height. It also verifies the relationships presented for turbulent viscosity. In addition, the near-wall behavior of the analytical relationships proposed for the tangential velocity is revised based on the boundary layer theory. Some common effective factors such as angular velocity, discharge time, and liquid height are also investigated. The volume of fluid (VOF) model and the Transitional SST k-ω turbulence model were used to solve the two-phase turbulent flow. The results show that increasing the gas pressure from 1 to 5 bar and its direct impact on the liquid surface significantly accelerates the formation of the vortex and the critical height. This phenomenon causes the air core to reach the inlet of the outlet pipe approximately 7 seconds earlier after the start of the liquid discharge. As a result, much more liquid mass remains in the tank. The increase in the angular velocity of the reference frame from 0.1 to 1 rad/s also causes the critical height to be reached much earlier and the remaining liquid mass to increase by 32 kg. In addition, the amount and variations of turbulent viscosity differ significantly from the semi-empirical constants, limiting their use to certain flows. [ABSTRACT FROM AUTHOR]

Knock is one of the main obstacles to improving the thermal efficiency of spark-ignition internal combustion engines. Although knock has been widely studied and accepted as a result of end-gas auto-ignition, the fundamentals regarding auto-ignition behaviors are still not fully revealed. In this study, the ignition behaviors of primary reference fuels were investigated in an optical rapid compression machine equipped with a quartz combustion chamber allowing for visualizing the combustion process from the lateral view. By combining both the lateral view and the top view photography, ignition behaviors under vortex-existing conditions with a creviced piston and vortex-minimized conditions with a flat piston were comprehensively analyzed to reveal the impact of the vortex on the ignition behaviors of PRF fuels. The influence of fuel reactivity was also investigated. The results showed that mild ignition was prevalent under large Da* numbers. The occurrence of mild ignition was closely related to the ignition delay time of the mixture, and the critical ignition delay time was not fixed but decreased with increasing initial temperature. The propensity of mild ignition could be boosted under vortex-existing conditions due to the increasing hotspot formation probability. Vortices were demonstrated to be capable of mitigating knock intensity via 1) the buffer effect of surrounding burned regions on the shock waves generated from surrounded unburnt pockets; 2) a larger burned mass fraction at the instant of the final ignition under vortex-existing conditions. The results also showed that strong ignition was more likely to occur under vortex-minimized conditions. Besides, higher fuel reactivity also could increase the probability of strong ignition occurrence. Compared with the creviced piston, the use of the flat piston could shift the ignition regime towards regions with higher Re t and lower Da t in the Da t - Re t diagram, where the strong ignition is less pronounced. [ABSTRACT FROM AUTHOR]

Shear banding in amorphous metals originates from the activation and percolation of flow units. To uncover the self-assembly dynamics of flow units in metallic glasses, a rectangular sample with two flow units embedded in the matrix undergoing simple shearing was analyzed using finite element simulations. The vortex evolution behavior, including activation, growth, and collapse during the self-assembly of flow units, was revealed. It was found that the formation of a mature vortex indicates the onset of yielding, and the collapse of the vortex represents the percolation of flow units or shear localization. The effects of initial free volume distribution and the distance between flow units on vortex behavior were also studied. Increasing the initial free volume concentration within flow units or the matrix leads to a gentler vortex evolution process and better homogeneous plasticity. The shape of vortex tends to be "flatter" with the increase in flow units' spacing, and the optimal spacing was found to maximize the strength of the material. [ABSTRACT FROM AUTHOR]

Low-frequency buffeting is a common problem in automobile wind tunnels, it induces pulsations of pressure and velocity in the test section. A 1:15 3/4 openjet return-type scaled wind tunnel was used for this research, and numerical simulations and tests were implemented to study the flow characteristics of the jet shear layer in a model wind tunnel. The results show that guide devices on the inner wall of the nozzle can effectively reduce the low-frequency buffeting, but the presence of the devices deteriorated the axial static pressure gradient of the flow in the test section. The shape of the guide devices was optimized through the Explorative Gradient Method, and numerical simulations were carried out. An optimal shape can effectively reduce the low-frequency buffeting and ensure flow field uniformity in the test section. Finally, the reliability of the numerical simulation and the practicability of the optimal case were verified through a hot wire test and a microphone test. [ABSTRACT FROM AUTHOR]

The micro tube bank model is a commonly used structure in microelectro mechanical cooling systems. Flow across a micro tube bank is a basic benchmark for analyzing flow resistance and heat transfer capability. In this paper, the flow around a micro tube bank model was studied both experimentally and numerically. Micro Particle Image Velocimetry technology was used to measure the flow field at different inlet flow rates. The laminar flow model, S-A model and standard k-ε model were used to calculate the flow field inside the micro tube bank model. By comparing the results from the three numerical models with the experimental results, there is a certain gap between them can be noted. However, it was found that the standard k-ε model is better than laminar model and S-A model in the comparison between numerical results and experimental results. In conclusion, the standard k-ε model is more suitable for the numerical calculation of the flow field around a micro scale tube bank model. [ABSTRACT FROM AUTHOR]

Moving model simulations have been a key method of predicting the aerodynamic performances of High-Speed Trains (HSTs). Ideally, the aerodynamic characteristics of a train moving or being blown by the wind are the same with appropriate ground configurations. In a numerical simulation, there are differences due to interpolation errors and errors caused by model movement. The impact of the error caused by the movement on the result is not known. Therefore, in this study, stationary and moving cases were used to assess the magnitude of the movement's effect using the Improved Detached Eddy Simulation (IDDES) method. A wind tunnel test validated the numerical algorithm at 60 m/s and a common yaw angle of 0°. Moreover, the spatial and time discretization satisfied the high accuracy requirements, as determined through a mesh independence study and convective Courant number testing. The time-averaged drag coefficients predicted by the moving case were similar to those of the stationary case, especially the total drag coefficients. In contrast, differences were determined in the stationary and moving cases in terms of the flow structure and slipstream. The motion encouraged the streamwise vortices around the tail car and the wake vortices to expand along the spanwise direction and the wall-normal direction, and the vortex cores shifted away from the outer surface of the vehicle. As a consequence, the average value and the standard deviation of the slipstream increased. Therefore, moving model simulations require more caution. These findings can help researchers make directional corrections in the numerical simulation of train-tunnel systems. [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation of the interaction among wave, flow and a fixed cylinder using the naoe-FOAM-SJTU solver, which is a viscous solver for hydrodynamics based on OpenFOAM. The simulation considers the strong nonlinear interaction among a regular wave, flow, and a single fixed cylinder due to viscosity, which is common in offshore structures. The study focus on the vortex induced by viscosity and its significant role in hydrodynamic performance computation. A mesh convergence study is conducted prior to the simulation, and a proper set of mesh is chosen. The simultaneous generation of the regular wave and flow is realized using the numerical field boundary, and the wave propagation is validated. The results of wave elevation and pressures captured by wave gauges and probes around the fixed cylinder are compared with experiment results. The structure of vortices is displayed at significant times, and the phenomena of wave elevation and pressure changes around the cylinder are analyzed in detail using the Omega-Liutex identification method. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[Display omitted] • Anisotropic meta -atoms are designed for the generation of four-channel vortex beams via a single metasurface. • Functions of metasurfaces are dynamically adjusted by altering the polarization of incident wave and the state of VO 2. • The generated vortex beams own contrasting OAM modes, quantities, and deflection directions. In recent years, vanadium dioxide (VO 2) has drawn enormous attention in dynamic electromagnetic (EM) manipulation, owing to its mild phase change condition and prominent diversity of optical characteristics. In this paper, anisotropic meta -atoms integrating VO 2 are proposed to obtain four polarization-multiplexing channels. The meta -atom is composed of two stacking metal–insulator–metal (MIM) structures. For the modulation of EM wavefront in desired manners, a meta -atom database composed of 256 meta -atoms is elaborately designed. Applying the meta -atom database and the degree of freedom in interfacial phase distribution, two metasurfaces are demonstrated in the verification of four-channel polarization-multiplexed vortex beams. The firstly proposed metasurface realizes the generation of four vortex beams with different topological charges. Each channel is dependent on the polarization of the incident wave and VO 2 state. The further investigated metasurface achieves simultaneous control over the reflection direction, quantity, and mode of vortex beams under different VO 2 states and polarization states of incident wave. In addition, designed metasurfaces exhibit wideband effect for over 100 GHz. The proposed design method enables four-channel generation of vortex beams using a single metasurface, and may have potential applications in dynamic and integrated terahertz communication. [ABSTRACT FROM AUTHOR]

To assess unsteady vortex interaction between rim seal purge flow and upstream stator, numerical investigations were conducted under different purge flow rates. The vortex distributions for the stator and cavity were investigated and the interaction processes near the cavity exit, in particular the vorticity change resulting from the ingress and egress, were analyzed. Results show the intensity of hub passage vortex (HPV) and hub trailing shedding vortex (HTSV) at stator exit is decreased as a consequence of enhancing blockage effects caused by the egress flow. However, when the purge flow rate increases, from stator exit to downstream of cavity exit, the reduction in the intensity of two vortices is weakened as the extrusion of egress flow thins their vortex tubes. The vortex inside the cavity is generated as the combined effect of relative rotation of cavity walls and nonuniform circumferential pressure mainly imposed by upstream stator. The ingress leads the positive axial vorticity near the stator hub to ingest into the cavity and eject into the main passage due to the blockage of purge flow. Furthermore, the interaction between the ingress of the mainstream and purge flow produces local negative axial vorticity. The egress flow carries negative axial vorticity mainly originated from the rotational cavity wall, and enters into the main flow passage near the rotating hub, then locations of HPV and HTSV move to the mid-span slightly with the extrusion of egress flow. [ABSTRACT FROM AUTHOR]

The effects of a Trapped Vortex Cavity (TVC) on the aerodynamic performance of a NACA 0024 airfoil at a constant angle of attack (AoA) of 14° were investigated in this study. It was observed that mass suction (MFR) was required to stabilise the vortex within the cavity segment. Lift to drag ratio (L/D) and MFR were chosen as performance objectives, along with a fully attached flow constraint (flow separation at X/c ≥ 95% ). Parametric analysis was carried on the baseline airfoil with and without suction and compared to the airfoil with TVC with and without suction. It was observed that L/D increases as MFR increases for a baseline airfoil, and flow separation is delayed at high suction values (MFR = 0.2 kg/s). The TVC modifies the pressure distribution on the baseline airfoil when MFR is applied to the cavity section and there is a significant increase in lift; thus, L/D increases and flow separation is delayed. A lower value of MFR = 0.08 kg/s is sufficient to stabilise the vortex and improve the efficiency of the TVC airfoil. The findings of these parametric studies were used to do a multi-objective optimisation using a genetic algorithm to attain the desired cavity shape while achieving the largest L/D and the lowest MFR (that is proportional to the power required for control) with a fully attached flow constraint. It was found that mass suction and cavity shape both had an equal influence on flow control. The Pareto optimal front yielded a series of optimum designs. One of them was subjected to an off-design analysis in order to validate its performance at other incidences. It was observed that it performs better than the baseline airfoil, with an improved L/D and an increase in stall angle from 10° to 14°. [ABSTRACT FROM AUTHOR]

Unsteady pressure pulsation and fluid force induced by flow instabilities in the centrifugal pump is an important cause of vibration, which is detrimental to the safe operation of the pump. In this study, we numerically investigated the pressure pulsation and radial force in a low-specific-speed centrifugal pump by using the detached-eddy simulation method. We also performed a vibration displacement experiment on the shaft of the centrifugal pump. The vortex identification method was introduced to clarify the internal correlation between unsteady flow structures with pressure pulsations. The results showed that the pressure pulsations at the impeller outlet were closely associated with the periodic vortex shedding from the blade pressure surface. The rotor-stator interaction between a relatively big trailing vortex core and volute tongue generated larger pressure pulsation and radial force in the pump at a low flow rate. Under a large flow rate, the trailing vortex core was easily broken and dispersed, and this resulted in smaller pressure pulsation and radial force compared with that at a low flow rate. Under the design flow rate, the pressure pulsation intensity and the radial force in the impeller were smaller than that under the off-design flow rate. Compared with the spectra between the radial force on the impeller and radial displacement on the shaft, they both presented higher amplitude at the shaft frequency. The vibration of the pump shaft was closely related to the radial force on the impeller. [ABSTRACT FROM AUTHOR]

Inducers in centrifugal pumps are generally placed upstream to increase the pressure before the impeller and prevent cavitation occurrence. Their general goal is to obtain a positive impact on the performances of a pump in a two-phase regime. Cavitation phenomenon has been the subject of many studies; however, the influence of the presence of dissolved gas in the liquid pumped under particular operating conditions remains not sufficiently explored. To the best of our knowledge, aviation jet fuel cavitation is moderately documented. In the present work, we conducted an experimental study on two three-bladed axial inducers at partial flow rates only in cavitating and noncavitating regimes. The experimental work used aviation jet fuel, water, and water with dissolved content of CO2 at constant temperature in two closed loops with transparent test sections. In one tank, a specific device is placed to inject a controlled quantity of CO2 and to dissolve it in water. We achieved a comparison of the flow dynamics through the use of a high-speed camera with a sampling rate of 1000 Hz. The results show inducers' water-CO2 cavitation performances to be in good agreement with aviation jet fuel cavitation results. [ABSTRACT FROM AUTHOR]

Air-breathing propulsion has the potential to decrease the cost per kilogram for access-to-space, while increasing the flexibility of available low earth orbits. However, to meet the performance requirements, fuel-air mixing inside of scramjet engines and thermal management still need to be improved. An option to address these issues is to use intrinsically generated vortices from scramjet inlets to enhance fuel-air mixing further downstream, leading to shorter, less internal drag generating, and thus more efficient engines. Previous works have studied this vortex-injection interaction numerically, but validation was impractical due to lack of published experimental data. This paper extends upon these previous works by providing experimental data for a canonical geometry, obtained in the T4 Stalker Tube at Mach 8 flight conditions, and assesses the accuracy of numerical methodologies such as RANS CFD to predict the vortex-injection interaction. Focus is placed on understanding the ability of the numerical methodology to replicate the most important aspects of the vortex-injection interaction. Results show overall good agreement between the numerical and experimental results, as all major features are captured. However, limitations are encountered, especially due to a localised region of over predicted heat flux. [ABSTRACT FROM AUTHOR]

New observations are reported of the processes leading up to lean blowoff (LBO) in a two-dimensional confined bluff body flame by visualizing LBO from a spanwise perspective. Time-resolved OH* chemiluminescence imaging simultaneous with particle image velocimetry are used to characterize the spanwise structure and dynamics. For reacting conditions, newly observed large-scale corner vortex structures (CVS) are present downstream of the bluff body inside the recirculation zone near the span walls. The CVS are orthogonal to the conventional recirculation zone observed in a bluff body flow, and the CVS are absent under non-reacting conditions. As the equivalence ratio is decreased, the vorticity and circulation of the CVS increase, contributing to significant nonuniformity across the spanwise direction both inside the recirculation zone and on the surrounding combustion. Approaching LBO, increased quantities of vanishing combustion near the span walls implies increased quantities of reactants entering and diluting the recirculation zone. Since cold reactant entrainment into the recirculation zone has been suggested as a possibly important LBO contributing factor, the current study suggests that this wake disruption mechanism begins much earlier than previously thought. The CVS are also the final regions of the flow to extinguish before LBO is complete, emphasizing that LBO is a highly three-dimensional process. A bluff body with an aspect ratio three times larger was also investigated, and the LBO process is observed to remain qualitatively similar with significant spanwise nonuniformity and containing the CVS. This paper intends to improve the three-dimensional understanding of two-dimensional bluff body stabilized premixed flames approaching LBO. [ABSTRACT FROM AUTHOR]

Flow around the Guide vane! (GV) in Francis turbine differs with the shape of hydrofoils. The difference in the pressure of fluid travelling 10 pressure side and suction side of GV contributes to flow behavior. This study presents the numerical technique using alternative clearance gap method to predict the flow around GV and its consequent effect on turbine performance. GV profile has a significant effect on the performance of the turbine with sediment contained flui i flow. In this paper, symmetrical NACA 0012 and cambered NACA 2412, NACA 4412 hydrofoils are studied introducing 0 mm, 2 mm, and 4 mm clearance gaps. Vortex filament can be seen when fluid leaves the clearance gap due to the leakage flow occurring through the gap. The intensity of vortex leaving clearance gap rises with an increase in the size of the clearance gap. However, in the case of asymmetrical GV profile, the velocity of fluid travelling along the vortex compared to that of symmetrical hydrofoil is lower. In case of low specific speed Francis turbines, this vortex is found to be a major reason to erode the runner surface d ie to high velocity of a sand particle travelling with them. With the alternative clearance gap approach, this paper compares the pressure pulsation downstream o f GVs contributed by leakage flow for three NACA profiles, whose frequency is half of blade passing frequency. [ABSTRACT FROM AUTHOR]

Vortex is the basic obstacle envisaged in the morning glory spillways that can lead to the reduction of spillway efficiency due to decreasing the discharge coefficient. It is well known that the vortex breakers are the best for increasing the discharge coefficient of spillway. In the present study, the physical model of morning glory spillway is constructed to investigate the influence of the number and geometry of pyramidal vortex breakers on discharge coefficient of the spillway. A set of empirical equations are developed as predictors for the discharge coefficient due to pyramidal vortex breakers. Sensitivity analysis is performed to explore efficient parameters on the discharge coefficient. Findings show, a group of six vortex breakers causes a significant increase in the Performance Index for discharge coefficient up to 50.97% in the crest control and an increase up to 16.13% in the orifice control compared to the normal morning glory spillway. [ABSTRACT FROM AUTHOR]

Copyright of Industria Textila is the property of Institutul National de Cercetare-Dezvoltare pentru Textile si Pielarie and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• The left ventricular (LV) vortex is an important predictor of adverse outcomes in congestive heart failure patients. • Higher circulation and altered energy dissipation are seen in patients with tetralogy of Fallot. • Posterior paravalvular leak (PVL) post-transcatheter aortic valve replacement has more negative impact on LV flow compared to anterior PVL. Various forms of vortex formation in the cardiovascular system convey valuable information regarding the function of heart and great vessels. The vortex ring that forms during systole in the aortic sinus is the first that was recognized and the asymmetric transmitral vortex ring that forms in the left ventricle during diastole has been most commonly used for diagnosis and follow up of heart failure patients. Adverse vortex interaction in the heart can also occur due to valvular regurgitation and may have energetic consequences to the heart. Furthermore, vortices do exist in other chambers such as the right ventricle and may even arise in the great arteries and veins due to congenital heart disease. Here, we summarize diagnostic and prognostic significance of vortices and vortex imaging in the heart, their applications in clinical medicine, and discuss how these flow features can be used to assess functional status of the heart. [ABSTRACT FROM AUTHOR]

The characteristics of the acceleration a and its correlation with the vortex core in the swirling flow are analyzed in this paper. The swirling flows of four swirl numbers (Sn = n S 0, 0.10, 0.20 and 0.36) are simulated by the direct numerical simulation, and the fluid mass particles from the inlet of the swirling flow are traced as a database for the current study. The correlations of the acceleration a with the vortex identification parameters of R and ω are quantified, where R is the parameter of the "Liutex"-method proposed by Prof. Liu, and its early version is "Rortex". The probability density functions of the included angles of a - R and a - ω are computed, which are used to clarify the geometrical configuration between a and R. The covariance coefficients between a and the parameters of various vortex core criteria (Q, λ2, ΩL, ΩR, ω and R) are computed and their relative levels of correlation are compared. Compared to the velocity, the expectation and the rms of the acceleration magnitudes and its projections on R and the plane perpendicular to R are computed for better explaining the correlation features between a and R. It is found that a and R are always either perpendicular or parallel to each other with the quantized included angles of ∠(a, R) = kπ/2, (k = 0,1,2). This confirms the role of R which works as the axis of the vortex exclusively. [ABSTRACT FROM AUTHOR]

We investigate the ground-state phases and spin textures of rotating binary dipolar Bose–Einstein condensates with Lee–Huang–Yang (LHY) correction and Raman-induced spin–orbit coupling (SOC) in a harmonic trap. Without rotation and SOC, the enhanced LHY correction can lead to structural phase transitions of the system. In the presence of SOC, a phase diagram as a function of the Raman coupling and LHY correction strengths is given. It is shown that the system exhibits rich and exotic quantum phases including quantum droplet (QD) phase with hidden vortex–antivortex pairs, droplet-stripe coexistence phase with hidden vortex–antivortex cluster, QD phase with visible triangular vortex lattice, annular stripe phase containing Anderson–Toulouse coreless vortex, and annular phase with vortex–antivortex pair necklace. In particular, for the rotation case, with the variation of Raman coupling strength the system displays complicated ground-state structures, such as layered structure of droplet necklaces and annular stripe with hidden layered vortex necklace and antivortex necklace, toroidal stripe phase with hidden antivortex necklace, and composite phase of visible square antivortex lattice and annular stripe. Furthermore, the system sustains fascinating novel spin textures and skyrmion excitations, including triangular half-antiskyrmion lattice, alternating meron-antimeron necklace, double-layer half-skyrmion necklace, and triangular half-skyrmion lattice. • Quantum phases of rotating BECs with SOC, DDI and LHY correction are investigated. • The system shows rich ground states depending on the competition between parameters. • The system sustains exotic spin textures and skyrmion excitations. [ABSTRACT FROM AUTHOR]

Recently, a new definition, called rortex, has been proposed to quantify the purely rotational motion of fluids. In this work, based on the DNS data we employed the rortex to assess and visualize the rotational motion and structure of vortex in swirling jets in comparison with other kinds of vortex criteria of Q, λ2, vorticity and Omega. The rortex vector, Omega, Q, and λ2 criteria are found to be better than vorticity for vortex core identification. The vector triangle formed by the Rortex R, nonrelational shear S, and vorticity ΩV is analyzed to give mechanical explanations, especially on the effect of non-rotational shear on rotation of fluids. In addition, the probability density distributions (PDF) of Rortex R, nonrotational shear S, and vorticity ΩV have been computed. The peak value of PDF of vorticity could be used to explain the pure rigid rotation effect and combination effects of rigid rotation and non-rotational shear. [ABSTRACT FROM AUTHOR]

The spacer grid is one of the most important parts of a fuel assembly for enhancing thermal-hydraulic performance. The mixing vane is a critical component of the spacer grid (or mixing vane grid) to produce lateral flow, turbulence, vortex, and other mixing mechanisms downstream of the grid. The design and arrangement of mixing vanes could influence the flow condition downstream, especially the lateral flow and vortex surrounding the rod bundle, which directly affect not only the hydraulics and heat transfer but also the critical heat flux. Understanding fundamental mixing characteristics is of great importance for fuel assembly design. Instead of using complicated geometries, this paper studies the lateral flow velocity and vortex in a simple 2 × 1 channel with a spacer grid in order to obtain the behavior of a single mixing vane and its effect on the downstream lateral velocity and vortex. Then, the effect of mixing vane arrangements on pressure drop is studied by researching the lateral velocity and vortex in the 2 × 1 channel with two mixing vanes. Several indexes that could reflect the mixing characteristics, such as lateral velocity and vortex, are introduced to assess the performance of the mixing vanes. Because of the presence of walls in both the experiment and the simulation, the lateral flow will reflect upon the impact of the obstruction walls or rods, which would cause vortex rotation. Rotation time and flow pattern are also studied in this paper. Qualitative and quantitative analyses are carried out to obtain the lateral velocity, the vortex angle, and its period of rotation. This work may be applied to the design and optimization of mixing vanes. [ABSTRACT FROM AUTHOR]

Three dimensional flows of complex non-Newtonian fluids in sudden expending pipes are numerically investigated in this paper. The distribution channels have one or multiple inlet pipes and one outlet pipe. The working fluids have a shear thinning behavior modeled by the Ostwald De Waele law. The effects of different parameters on the flow fields and pressure drop are explored. It concerns the effect of Reynolds number Re (from 0.1 to 600), power law index n (from 0.4 to 1), number of branching channels (nb = 1, 2, 3 and 4), spacing between the branching channels (l/D = 0.1, 0.2, 0.3 and 0.4) and the expansion ratio (d/D = 0.2, 0.35, 0.5, 0.6 and 0.8). Three-dimensional complex flows were observed in the downstream expansion for such multiple branching systems, especially when the spacing l/D is small, where an asymmetry of flows is observed and a third recirculation loop is formed. A considerable increase in pressure drop is found with the rise of Reynolds number, with increased power law index and decreased expansion ratio. However, only a slight increase is observed with decreased spacing ratio and it remained almost the same with increased number of branching channels. [ABSTRACT FROM AUTHOR]

Copyright of Avian Conservation & Ecology is the property of Resilience Alliance and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the present study, the performance of the vorticity confinement method has been improved by combining it with the vortex feature detection methods. In the conventional vorticity confinement method, the only parameter to apply or not to apply vorticity confinement is the non-zero value of vorticity. On the other hand, the presence of vorticity in some cases, like the boundary layer and the shear layer flows, does not imply the presence of vortices. Applying the vorticity confinement at these points can lead to errors, in addition to loss of solution time. In order to solve this problem, using the combination of vorticity confinement method and four methods of vortex feature detection (non-dimensional Q, non-dimensional λ2, non-dimensional modified Δ, and the S − Ω correlation) the vorticity confinement term is applied only in vortex regions. In order to investigate the effects of this combination, the compressible Euler equation has been investigated for the problem of two-dimensional stationary single vortex at Mach number 0.5. The results indicate significant positive effects in reducing the solving time, decreasing the sensitivity of the solution to the amount of confinement parameter and significant elimination of the oscillation. [ABSTRACT FROM AUTHOR]

The aortic valve is located at left ventricular outlet and is exposed to the highest pressure in the cardiovascular system. Problems associated with the valve leaflet movement can cause complications for the heart. Specifically, aortic stenosis (AS) arises when aortic leaflets do not efficiently open. In the present study, Lagrangian Coherent Structures (LCSs) were utilized by processing a variety of Computational Fluid Dynamics (CFD) models velocity vector data further to identify the characteristics of AS jets. Particularly, effective orifice areas (EOA) for different cases were accurately identified from unstable manifolds of finite time Lyapunov exponent (FTLE) fields. Calcified leaflets were modeled by setting the leaflet's Young modulus to 10 MPa and 20 MPa for moderately and severely calcified leaflets respectively while a healthy leaflet's Young modulus was assigned to be 2 MPa. Increase in calcification degree of the leaflet caused destruction of the vortex structures near the fibrosa layer of the leaflet indicating a malfunctioning for the movement mechanism of the leaflet. Furthermore, when we analyzed stable manifolds, we identified a blockage region at the flow upstream due to the stagnant blood here. Compared to a healthy case, for the calcified valve, this blockage region was enlarged, implying an increase in AS jet velocity and wall shear stress on leaflets. As a conclusion, results from the present study indicate that aortic leaflet malfunctioning could be accurately evaluated when LCS technique was employed by post processing velocity vector data from CFD. Such precise analysis is not possible using the Eulerian CFD approach or a Doppler echocardiography since these methods are based on only analyzing instantaneous flow quantities and they overlook fluid flow characteristics of highly unsteady flows. [ABSTRACT FROM AUTHOR]

High Pressure Torsion (HPT) is historically the first and is currently most common process of the severe plastic deformation (SPD). HPT is used for producing nanocrystalline structures in metals and alloys, as well as for cold welding of powders. The result of the HPT treatment is determined by the flow kinematics and the stress state of a material under deformation. P. Bridgman proposed a simple model for the initial assessment of shear strain in the sample during HPT. A number of recent investigations show that the true plastic flow during HPT can differ significantly from the simple model. We present in our report results of the FEM investigation of different types of flow during HPT. We propose a hypothesis that the vortex formation during the SPD process is caused by the local blocking of simple shear in a material under deformation. [ABSTRACT FROM AUTHOR]

The use of ferrofluids as shapeable external appendage to a submerged body and as a mean of vortex flow induction is studied in this paper. Ansys-CFX numerical results are validated against analytical problems and used to analyze the ferrofluid free surface shape affected by gravity, different magnets, and different densities of the surrounding non-magnetic fluids. It is demonstrated that the height, width, and curvature of ferrofluid can be controlled by magnet size and strength. It is also observed that ferrofluid mass loss may occur due to gravity, which should be addressed in designing a fluid appendage. Subsequently, vortex production inside the ferrofluid is investigated via a shear flow on the magnet. It is shown that ferrofluid can contain complex vortices while being shaped by the magnetic field, gravity, and the vortices. It is also observed that vortices inside the ferrofluid affect the flow of the surrounding fluid. Additionally, the effects of surface tension and viscosity are briefly analyzed to roughly show the importance of these parameters for further works. Overall, it is concluded that using ferrofluids as appendages for shaping and controlling fluid flow around submerged bodies seems to be practical and calls for more attention. [ABSTRACT FROM AUTHOR]

• Flow problem is analyzed of influence of a magnetic field on the hybrid nanofluid flow in a cavity due to a dipole. • The applied magnetic field as an agent of vortices generation the hybrid nanofluid flow is considered. • Lorentz force in the flow regime containing Cu and Fe 3 O 4 nanoparticles is used. • The numerical outcoming are achieved by Alternating Direction Implicit (ADI) methodology. A vortex is a location in a fluid where the flow revolves around an axis line, which may be flat or curved. Researchers must look at vortices whenever and wherever they are found since they are present in natural systems. The purpose of this investigation is to present an understanding of how the nanofluid flow (driven by an external mechanism) interacts with the magnetic field produced by a nearby paced magnetic source. While most of the scientific literature is enriched with investigations dealing with the problems assuming a uniform magnetic field occupying the flow field, the current analysis is devoted to studying the complex interaction of the spatially varying magneto force with the nanofluid flow. We have noticed that the magnetic field has caused the evolution of new vortices (which are very important while analyzing any flow model due to their importance in interpreting fluid mixing and mass transport phenomena) in the flow field, thus adding much more significance to our work. The single-phase model (SPM) has been used to describe the hybrid nanofluid whereas the numerical solution to the governing differential equations has been obtained by employing an algorithm based on the central difference discretization and the alternating direction implicit method. The governing factors for the current examination are the Reynolds number, the magneto variable, and the volumetric concentration of the nanoparticles, with the ranges, considered being 1 ≤ Re ≤ 150 , 0 ≤ M n ≤ 150 and 0 ≤ ϕ ≤ 0.2 , respectively. The analysis reveals that the Nusselt number (Nu) steepens noticeably at the enclosure's upper left corner. 20% increment in nanoparticle volume fraction may result in up to 72% boost in the Nusselt quantity whilst causing an up to 33% decrease in skin friction. Furthermore, compared to copper, iron oxide nanoparticles are shown to be more dependent on drag force. The flow field is dominated by two almost similar main vortices while there is no magnetic source, but as the magnetic source gets stronger, the bottom vortex gets stronger. It enlarges and constricts the top vortex, breaking it down while creating two new, weaker vortices. As it produces three vortices at comparatively lower values of the pertinent parameters, the Reynolds number functions as a catalyst for the action of the magneto force variable. Finally, the Nusselt quantity and frictional factor both significantly alter once the nanostructure is incorporated into the base fluid. [ABSTRACT FROM AUTHOR]

In this series of articles, the authors discuss various phenomena in fluid dynamics, which may be investigated via tabletop experiments using low-cost or home-made instruments. The seventh article in this series explores the formation, structure, and properties of antibubbles. [ABSTRACT FROM AUTHOR]

The spatial relationship between the energy dissipation slabs and the vortex tubes is investigated based on the direct numerical simulation (DNS) of the channel flow. The spatial distance between these two structures is found to be slightly greater than the vortex radius. Comparison of the core areas of the vortex tubes and the dissipation slabs gives a mean ratio of 0.16 for the mean swirling strength and that of 2.89 for the mean dissipation rate. These results verify that in the channel flow the slabs of intense dissipation and the vortex tubes do not coincide in space. Rather they appear in pairs offset with a mean separation of approximately 10η. [ABSTRACT FROM AUTHOR]

The hydraulic force on the reversible pump turbine might cause serious problems (e.g., the abnormal stops due to large vibrations of the machine), affecting the safe operations of the pumped energy storage power plants. In the present paper, the hydraulic force on the impeller of a model reversible pump turbine is quantitatively investigated through numerical simulations. It is found that both the amplitude of the force and its dominant components strongly depend on the operating conditions (e.g., the turbine mode, the runaway mode and the turbine brake mode) and the guide vane openings. For example, the axial force parallel with the shaft is prominent in the turbine mode while the force perpendicular to the shaft is the dominant near the runaway and the turbine brake modes. The physical origins of the hydraulic force are further revealed by the analysis of the fluid states inside the impeller. [ABSTRACT FROM AUTHOR]

The large eddy simulation(LES) of the flow characteristics in an annular jet pump (AJP) is conducted, and the flow characteristics are systematically analyzed from both time-averaged and instantaneous aspects. The jet expansion, the velocity distribution and the energy are considered to analyze the time-averaged evolution of the flow field in the AJP. The transient flow characteristics can also be acquired from the analysis of the turbulence intensity and the Reynolds stress. The simulation demonstrates that in the time-averaged characteristics, the potential cores increase linearly with the increase of the flow ratio. With the flow development, the jet half-width gradually increases and the residual energy coefficient decreases. Compared with the distribution of the time-averaged axial velocity, that of the instantaneous velocity is more complex and disorderly. The high intensity of the axial turbulence mainly occurs in the mixing layer and the near-wall regions of the diffuser. The annular distribution of the Reynolds stress is mainly in the mixing layer and the recirculation region. There is a low-stress zone between the mixing layer and the high-stress region in the wall-boundary layer. The intensity of the spanwise vortexes is larger than that of the streamwise vortexes, and therefore, the former make greater contribution to the total vorticity. This research provides a better understanding of the flow characteristics in the AJP. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the present study, vortices were generated in open channel flow with a cross-flow cylinder installed horizontally near the bed. Sediment pickup rates were then measured over the channel bed downstream the cylinder using a sediment lift. The experimental data show that the pickup rate increases exponentially in the presence of vortices. Two different relationships can be clearly observed between the pickup rate and the maximum root-mean-square (rms) value of the streamwise velocity fluctuation, one for the cylinder-obstructed flow and the other for the unobstructed flow. The results imply that the vortex-induced sediment pickup cannot be explained based on the traditional boundary layer theory. [ABSTRACT FROM AUTHOR]

Copyright of Revista de Climatología is the property of Revista de Climatologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Because the numerical simulation of soot production in turbulent flames is quite challenging, it is useful to consider simpler aerodynamic configurations retaining unsteady strain rate and curvature effects. The present article reports detailed numerical simulations of a planar vortex interacting with a sooting laminar diffusion flame formed by a parallel flow of acetylene and air. Calculations are carried out to reproduce the experimental data reported by Cetegen and Basu (2006). Compared to previous numerical works on this configuration based on simple two-equations soot models, a detailed numerical mechanism, accounting for 97 gaseous species and 59 solid BINs, is considered here to represent the chemistry in the gas phase and the production and oxidation of soot particles. Three different vortex strengths are considered and vortices are formed by pulsing the air or the fuel streams, allowing comparisons between the calculated soot-vortex-flame interactions with LII images. Calculations adequately retrieve experimental data when the vortex is initiated at the fuel side. Differences are observed when the vortex is formed on the air side. The simulations, however, are useful for examining strain rate and curvature effects on soot volume fractions of small spherical particles and large aggregates, and to study physical processes underlying the soot production. It is shown that the variability of the soot volume fraction is highly correlated to the response of soot precursors to flame curvature. Soot variability in the mixture fraction space depends on the behavior of large aggregates that, being characterized by high Schmidt numbers, are more sensitive to the convective motion imposed by the vortex compared to the gaseous phase. The observed behavior has to be reproduced by the models developed for numerical simulations in order to obtain an accurate prediction of soot production in turbulent flames. [ABSTRACT FROM AUTHOR]

Copyright of Ingenium is the property of Facultad de Ciencias Basicas e Ingenieria de Universidad de San Buenaventura, Revista Ingenium and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)