Vortex Movement Research Articles

Unsteady Hemodynamics in Intracranial Aneurysms With Varying Dome Orientations

Abstract Fluid loading within an intracranial aneurysm is difficult to measure but can be related to the shape of the flow passage. The outcome of excessive loading is a fatal hemorrhage, making it necessary for early diagnosis. However, arterial diseases are asymptomatic and clinical assessment is a challenge. A realistic approach to examining the severity of wall loading is from the morphology of the aneurysm itself. Accordingly, this study compares pulsatile flow (Reynolds number Re = 426, Womersley number Wo = 4.7) in three different intracranial aneurysm geometries. Specifically, the spatio-temporal movement of vortices is followed in high aspect ratio aneurysm models whose domes are inclined along with angles of 0, 45, and 90 deg relative to the plane of the parent artery. The study is based on finite volume simulation of unsteady three-dimensional flow while a limited set of particle image velocimetry experiments have been carried out. Within a pulsatile cycle, an increase in inclination (0–90 deg) is seen to shift the point of impingement from the distal end toward the aneurysmal apex. This change in flow pattern strengthens helicity, drifts vortex cores, enhances spatial displacement of the vortex, and generates skewed Dean's vortices on transverse planes. Patches of wall shear stress and wall pressure shift spatially from the distal end in models of low inclination (0–45 deg) and circumscribe the aneurysmal wall for an inclination angle of 90 deg. Accordingly, it is concluded that high angles of inclination increase rupture risks while lower inclinations are comparatively safe.

Water: a substance with unique properties

Water is a supramolecular aqua system with a single highly structurally dynamic network of hydrogen bonds. Since this grid is inhomogeneous in properties and structure, a proposed aquamezophase model of water takes into account the indicated heterogeneity and homogeneity of water. The peculiarities of intermolecular interactions for hydration and aquaclatratation, characteristic of water, are described. For the first time, the peculiarities of the chemistry and energy of water during vortex motion were revealed. This made it possible to propose a mechanism of action for vortex tubes, a cyclone of J. Rank, and aqua-vortex heat generators. Due to the vortex movement, the aquatic systems of the living organisms actively show restorative properties and become a source of energy necessary for life. Due to the thermodynamic nonequilibrium, openness, nonlinearity, and self-oscillating properties, water is a source of very weak acoustic and electromagnetic aqua emissions in a wide frequency range from fractions of Hz to 1017 Hz, which are recorded as emissions from the end of the 20th century. Since water is a source of radiation and is sensitive to external radiation, water is an aqua-radio system. Under even weak external influences, water is characterized by phase transitions of the second order under external weak influences, at which its ΔUtotal ≈ 0. At the first resonance stage, a quickly coordinated and conjugated transformation |ΔUfree|↔|ΔUconnect| occurs, which changes the properties of water. The second stage is a slow return to its original state, i.e., structural-temporal hysteresis is observed. The change in the properties of water as a result of a phase transition of the second kind is called aquacommunication. Given that living things in molecular composition consist of 99% of water, all living things are also aqua-systems.

Coupling analysis of contra-rotating fan interstage pressure pulsation and blade vibration based on wavelet reconstruction.

In recent years, the flow characteristics research of the interstage region in counter-rotating axial fans in terms of fluid dynamics has attracted much attention. Especially, the dynamic relationship between interstage pressure pulsation and blade vibration in counter-rotating axial fans has not yet been clarified. This paper performs the signal processing method of wavelet decomposition and reconstruction in time-frequency analysis process. Under different flow conditions, weak-coupling numerical simulation program is employed to analyze the fluid-structure coupling interaction between interstage pressure pulsations and blade vibrations in counter-rotating axial fans. The results indicate that the fluid-structure coupling interaction field in the interstage of counter-rotating axial fans mainly excites the first-order vibration of the second-stage blade. At the same time, the consistency between the pulsation frequency and the vibration frequency of the airflow reflects the good coupling property. Two stage blades cut the airflow to cause field changes and airflow pulsation, and then, airflow pulsation causes blades deformation and produces vibrations of the same frequency at the blade. The deformation of the blades, in turn, causes the flow field changes. Rotating stall, vortex movement and breakdown produced low-frequency airflow pulsation and vortex vibration of the blade.

Effect of ground on flow characteristics and aerodynamic performance of a non-slender delta wing

The aerodynamic performance and the structure of vortical flow on a delta wing are affected by the influence of the ground in take-off and landing stages. In this context, the effect of the ground on a delta wing having a sweep angle of 40° was investigated by employing Particle Image Velocimetry (PIV), aerodynamic force measuring system and the dye flow visualization technique. Flow characteristics of delta wing were examined under two different angles of attack, α=8° and 11° and variation of the distance between trailing edge of the wing and ground, h normalized with the root chord length, c of the wing. It was observed that the existence of the ground attenuates the magnitude of peak values of primary and secondary vortices due to incomplete development of vortices. The ground effect caused the outboard movement of the leading-edge vortex in a spanwise direction as well as an increase in the size of vortices. Furthermore, the presence of the ground induced a decrease in Strouhal number, St due to the slowing down of vortex formation. Lift and drag coefficient, CL, and CD of the delta wing were observed to increase with descending from unbounded flight region into ground effect region. Finally, it was found that CL/CD increases by reducing the distance between ground and wing, h/c, and a rise of CL/CD is much more effective under the lower angles of attack, α.

ОЦЕНКА ГЕОДИНАМИЧЕСКОЙ СИТУАЦИИ ВОРОНЕЖСКОГО КРИСТАЛЛИЧЕСКОГО МАССИВА ПО ГЕОДЕЗИЧЕСКИМ ДАННЫМ

Repeated geodetic measurements allow you to evaluate such geodetic elements as coordinates, heights, and directions. And also represent discretely the field of displacement vectors of geodesic points. The obtained vectors allow us to determine the stress-strain state of the earth's surface according to the accepted model. There is a reasonable opinion about the significant presence of rotational (vortex) movements in geodynamic processes. Here, the corresponding algorithms are used for the territory of the Voronezh Crystal massif. Separately, it is possible to calculate the differential characteristics of the vector field, called divergence (div) and rotor (vortex, rot, curl). The article proposes to determine the rotor field from discrete geodetic observations of displacement vectors on the surface of the studied territory. The most important continuation of this research work is the method of mathe-matical modeling of geodynamic systems for predictive purposes. For the study of complex (nonlinear) geodynamic processes, an appropriate mathematical basis should be chosen. Here, attention is drawn to the involvement of the mathematical foundations of field theory. To evaluate the characteristics of vector fields when using repeated geodetic measurements, the method of finite elements can be used. Dividing the territory under study into triangles allows us to determine the deformation characteristics after calculating the elements of the strain tensor. In particular, the value of the angular velocity of the triangle rotation relative to its center of gravity is found. Next, it is easy to calculate the value of the rotor. The example given in the article of real geodetic observations on the Voronezh crystal massif confirms the possibility of predicting the location of an upcoming seismic event – an earth-quake.

Вплив внутрішньої динаміки когерентних вихрових структур, що взаємодіють між собою, на генероване звукове поле

The article is dedicated to the glowing memory of the talented Ukrainian scientist-mechanic, professor, doctor of physical and mathematical sciences Vyacheslav Vladimirovich Meleshko. The sound fields of several coherent vortex structures interacting with each other were calculated using the moment model (MZS-model) of the first and second orders. In the first-order MZS-model, vortices are described by point vortices, in the second-order MZS-model--by Kirchhoff vortices. Sound fields as a result of vortex interaction are calculated using the Lighthill's acoustic analogy under Powell's formulation. The spectrum of the sound field in the description of coherent vortices by point vortices is characterized by a single frequency band, which reflects the motion of the vortex centers of vortices (large-scale vortex movements). Taking into account the inner vortex dynamics leads to the expansion of spectrum and level increasing of calculated sound: the lower band describes the motion of the vorticity centers of spots, the higher band describes the internal dynamics of the vorticity. It is shown that large-scale vortex movements can be modeled by point vortices, when the sound spectrum of distributed vortices is clearly divided into bands and the width of the lower frequency band is close to the width of the sound spectrum from point vortices. The presence of an upper frequency band in the sound field of interacting vortex spots does not allow us to describe the distributed vortices as point vortices when constructing a sound source, since such a simplification leads to a significant underestimation of the level of the calculated sound field.

Research on identification of vortex structure in oxy-fuel heating furnace based on vortex identification method

ABSTRACT MILD oxy-fuel combustion has become the subject of study as it can improve the combustion efficiency and reducing the emission of harmful gases. However, there are few researches on the vortex motion of Oxy-fuel combustion, and there is no clear definition for the application of gas vortex. In this paper, based on the experimental and simulation data of the heating furnace, the distribution of eddy motion was analyzed from aspects of the turbulent vortex formation, formation, and movement of the vortex. In this paper, the vortex structure of the furnace is analyzed by using the Q criterion, method, and method. We found that both Q criterion, criterion, and method could identify the vortex structure in the furnace, but method could identify the vortex structure that could not be identified by the other two methods. could display more vortex structures and could identify both weak and strong vertices, with stronger recognition ability.

Investigation on the Flow Field Entropy Structure of Non-Synchronous Blade Vibration in an Axial Turbocompressor.

In order to explore the inducing factors and mechanism of the non-synchronous vibration, the flow field structure and its formation mechanism in the non-synchronous vibration state of a high speed turbocompressor are discussed in this paper, based on the fluid–structure interaction method. The predicted frequencies fBV (4.4EO), fAR (9.6EO) in the field have a good correspondence with the experimental data, which verify the reliability and accuracy of the numerical method. The results indicate that, under a deviation in the adjustment of inlet guide vane (IGV), the disturbances of pressure in the tip diffuse upstream and downstream, and maintain the corresponding relationship with the non-synchronous vibration frequency of the blade. An instability flow that developed at the tip region of 90% span emerged due to interactions among the incoming main flow, the axial separation backflow, and the tip leakage vortices. The separation vortices in the blade passage mixed up with the tip leakage flow reverse at the trailing edge of blade tip, presenting a spiral vortex structure which flows upstream to the leading edge of the adjacent blade. The disturbances of the spiral vortexes emerge to rotate at 54.5% of the rotor speed in the same rotating direction as a modal oscillation. The blade vibration in the turbocompressor is found to be related to the unsteadiness of the tip flow. The large pressure oscillation caused by the movement of the spiral vortex is regarded as the one of the main drivers for the non-synchronous vibration for the present turbocompressor, besides the deviation in the adjustment of IGV.

Seedingless measurement of density fluctuations and flow velocity using high-speed holographic interferometry in a swirl-stabilized flame

Environmental protection is today’s major issue in the development of turbomachines. Especially, the reduction of pollutant and noise emission of aero engines and ground based gas turbines for power plants is a central task. Therefore, an improved understanding of the occurring complex flow phenomena in such turbomachines is necessary, which requires the investigation of influence and interaction of several process and flow quantities. A simultaneous detection of these quantities is needed in order to analyze the interaction by means of correlation. We present a new approach for simultaneous measurement of density fluctuations and advection velocity inside a turbulent flow without any invasive treatment of the process. Our approach is based on recent developments in the fields of high-speed camera technique and digital processing power, enabling pixel-wise detection of line-of-sight density oscillations and digital signal correlation with a high spatio-temporal resolution of 140μm2 using 79000 pixel at a frame rate of 120kHz, where the velocity measurement is performed by correlation of density vortex movement. A comparison with particle-based velocity detection is made in order to achieve new insights towards the still complicated interpretation of density-based velocity estimation.

Effect of Ground Boundary Condition on Near-Field Wingtip Vortex Flow and Lift-Induced Drag

Abstract The ground proximity is known to induce an outboard movement and suppression of the wingtip vortices, leading to a reduced lift-induced drag. Depending on the ground boundary condition, a large scatter exists in the published lift-induced drag and vortex trajectory. In this experiment, the ground boundary condition-produced disparity in the vortex strength and induced drag were evaluated. No significant discrepancy appeared for a ground distance or clearance larger than 30% chord. As the stationary ground was further approached, there was the appearance of a corotating ground vortex (GV), originated from the downstream progression of a spanwise ground vortex filament, which added vorticity to the tip vortex, leading to a stronger tip vortex and a larger lift-induced drag compared to the moving ground. For the moving ground, the ground vortex was absent. In close ground proximity, the rollup of the high-pressure fluid flow escaped from the wing's tip always caused the formation of a counter-rotating secondary vortex, which dramatically weakened the tip vortex strength and produced a large induced-drag reduction. The moving ground effect, however, induced a stronger secondary vortex, leading to a smaller lift-induced drag and a larger outboard movement of the tip vortex as compared to the stationary ground effect.

Effect of gusty inflow on the jet-switching characteristics of a plunging foil

The effect of stochastic inflow fluctuations on the jet-switching characteristics of a harmonically plunging elliptic foil at a low Reynolds number regime has been analyzed in the present study. The inflow fluctuations are generated by simulating an Ornstein–Uhlenbeck process—a stationary Gauss–Markov process—with a chosen correlation function. In the absence of fluctuations, quasi-periodic movement of the wake vortices plays a key role in bringing out jet-switching at κh ≥ 1.5. However, fluctuating inflow alters the organized arrangement of the vortex street even at a lower κh (κh = 1.0), giving way to an advanced jet-switching onset. More frequent switching with a larger deflection angle is also observed at κh = 1.5 as compared to the no fluctuation case. Effects of inflow timescales on the deflection angle and switching frequency of the wake are investigated by varying the input correlation-lengths. The underlying flow physics are investigated through a qualitative study of the near-field interactions as well as various quantitative measures derived from the unsteady flow-field.

Experimental investigation of a pitch-oscillating wind turbine airfoil with vortex generators

The inflow shear and turbulence, tilt or yaw misalignment, and tower passage lead to dynamic stall on turbine blades. The effects of vortex generators (VGs) on the aerodynamic performance of a typical wind turbine airfoil, namely, DU91-W2-250, are measured under the background that VGs are gradually and widely installed for energy improvement. The experiment is carried out in a wind tunnel at the Reynolds number of 3×105. The oscillation of the testing model is driven by a servo motor, and the aerodynamic performance is measured using an ESP-64 scanner. The flow separation is visualized with tufts. The obtained results show that the installation of the VGs could effectively control both static stall and dynamic stall of the airfoil because VGs cause a lower pressure region on the airfoil suction surface near the leading edge and a pressure plateau that appears later than in the smooth airfoil. Meanwhile, the VGs could effectively increase the adverse pressure gradient and lead to an early transition to delay the flow separation before stall and force the flow field in the turbulence state. It is also found that the VGs could reduce the pressure fluctuations caused by the turbulence of the boundary layer during dynamic stall. Furthermore, the VGs are also found to be useful in suppressing the span-wise movement of vortices. However, the VGs could not improve the aerodynamic performance in the deep stall region under none of the static and dynamic conditions.

Effect of the ballast height on the slipstream and wake flow of high-speed train

The improved delayed detached-eddy simulation (IDDES) method based on the shear-stress transport (SST) κ-ω turbulence model was employed to investigate the ballast height influence on aerodynamic performance at Re ​= ​9.12 ​× ​106. Both time-averaged and instantaneous slipstreams and near-wake flow structures and associated slipstream velocity distributions are compared for four cases. Results reveal that the mean lift force coefficient decreases with increasing ballast height. At the Technical Specifications for Interoperability (TSI) trackside position, the maximum slipstream velocity with a ballast height of 1.825 ​m (Case 3) is 97.4%, 15.6% and 11.7% lower than with a ballast height of 0 ​m (Case 1), 0.825 ​m (Case 2) and 2.825 ​m (Case 4), respectively. The TSI values in Case 3 ​at both the trackside and platform positions are the lowest. In the wake region, increasing the ballast height greatly constrains the outward and downward movements of vortices. The slipstream velocity in the wake region in Case 3 is the lowest among all cases. In this study, we found that Case 3 greatly decreases the slipstream velocity around the train and improves the flow structure in the wake region, which reduces the risk to workers and equipment along the railway.

A numerical and experimental investigation of wave generated by submerged landslides

The Weakly-Compressible Moving Particle Semi-implicit (WC-MPS) approach is applied to investigate the wave propagation and the flow fields induced by sliding blocks. Since there are already studies focusing on an inclination slope of 45°, two slope angles, 40° and 50°, are used to obtain the additional experimental results. Sliding blocks are released under water, where the top edges are parallel to the water surface. The simulation results are compared to the experimental measurements both on the water surface and the velocity distribution at specific locations. To analyze the flow fields, contour and vector plots illustrate the flow characteristics for the entire velocity distribution in the simulation domain along with the vortex movements from the sliding block. Two case scenarios are presented to investigate the velocity distribution of the sliding block. For the first case scenario, seven cross-sections, including the front edge, the top edge, and the back edge of the sliding block were selected to further identify the characteristics of the horizontal and vertical velocity distributions. The second case scenario has five specific locations at the front, top and back edge of the block. A good agreement was obtained between the WC-MPS simulated results to the experimental data.

Features of the upper tropospheric cyclonic vortices of Northeast Brazil in life cycle stages

AbstractThe main purpose of the study is to explore in more detail the Upper Tropospheric Cyclonic Vortices (UTCVs) features over Northeast Brazil (NEB) in an attempt to improve weather forecasts. The various aspects of the life cycle features of the UTCVs over NEB are presented here, because these aspects have not been investigated in previous studies. Initially, the UTCVs were identified at 200 hPa, and then, they were identified at lower levels to analyse their vertical structure, using 6‐hr data for a 30‐year period (1984–2013) from the European Center for Medium Range Weather Forecasts' reanalysis (ERA Interim). An objective method was improved to obtain at first‐hand the trajectory and the vertical extent of the UTCVs over NEB. Some statistics results were consistent with previous studies related to relative frequency, duration and direction of movement. However, further results were obtained too. An average distance of 2,000 km for the UTCVs total travel was found. Of this average distance, 750 km was reached by UTCVs on the first day of the life cycle, leading to the presumption of a possible suppression of vortex movement that depends on a diabatic mechanism. We also found predominance of UTCVs without vertical tilt or with east tilt with increasing height. When considering life cycle stages (formation, maximum depth and dissipation), diversity was observed in intensity with stages, levels and seasons of the year, with spring exhibiting the most intense UTCVs over all seasons. Finally, our finding about interannual variability is novel. There was a tendency for the average number of UTCVs to be slightly higher during El Niño summers compared with La Niña summers.

Effects of guardrails on wind environment for vehicles and aerodynamic stability for bridges with box girders

Normally strong winds in mountainous areas possess potential threats to the safety of vehicles travelling over the long-span bridges. Generally, decreasing the porosity of the guardrails could improve wind environment for vehicles, while the changed flow field around the bridge’s girder may weaken the structural aerodynamic stability simultaneously. To solve the two seemingly contradictory issues, such a long-span suspension bridge in mountainous areas is taken as the case study, and the guardrails are optimized with different schemes. The effects on wind environment for vehicles under normal traffic conditions are first studied by computational fluid dynamics (CFD) simulations. The further effects on the aerodynamic stability of the bridge under extreme winds are then determined by wind tunnel tests, and the observed non-divergent flutter is explainedbythe change in dynamic flow field. Results show that reducing the porosity of guardrails does improve the wind environment above the bridge deck, and the improvement on wind environment increases with the increase in angle of attack. After closing the guardrails completely, however, the girder appears non-divergent vibration different from the linear theoretical flutter when the critical wind speed is exceeded. The different post-flutter behaviors at different angles of attack are mainly related to the synchronization condition between the movement of vortex and the motion of the girder.

Wind Turbine Tip Vortices under the influence of Wind Tunnel Blockage Effects

The current paper describes the characteristics of the tip vortex in the near wake of a three-bladed upwind horizontal axis wind turbine with a rotor diameter of 3 m. Phase-locked stereo particle image velocimetry measurements were carried out under the influence of the wind tunnel walls that create a high blockage ratio. The location of the vortex, convection velocity, core radius, and strength were investigated and compared with similar investigations, including different blockages cases. Additionally, the same performance of the wind turbine model was simulated in the open source wind turbine tool QBlade, using the lifting line free vortex wake module in the absence of the walls.The results showed that the location of the tip vortices was more inboard the tip and more downstream the tunnel compared to the simulations and similar experiments. The convection velocity remained similar in the axial direction and changed in the lateral direction, contributing to the delay of the movement of the tip vortex outboard the tip. The strength, based on the circulation, was found with a difference of 4% between simulation and experiment.

A numerical study of drag reduction performance of simplified shell surface microstructures

Antifouling and drag reduction are two critical issues for the shipping industry. Previous studies have revealed that biomimetic shell surfaces have distinct antifouling features. In this study, ten simplified surface microstructures with the same cross-section area are designed based on the antifouling scale of the shell surface morphology. Turbulent flow over the riblet structures is simulated using a finite volume based CFD solver with the Shear Stress Transport k-ω model to examine the effects of the riblet structures on skin friction with mean flow velocities ranging from 1 to 7 m/s. The corresponding dimensionless square root of the groove cross-section area is lg+≈4.5–25.6. Considering the predicted drag performance and issues concerning riblet tip rounding and fabrication, an optimal geometry with both antifouling and drag reduction features has been identified. The present study confirms that the riblets lift off streamwise vortices, pushing the high turbulent kinetic energy region away from the surface, and impede the spanwise movement of streamwise vortices, leading to skin-friction reduction. Further, the investigation of the effect of the riblet interval on the drag behaviour indicates the existence of a balance point between the wetted perimeter and the total area of the riblet surface for minimizing drag.

Vortices as Brownian particles in turbulent flows.

Brownian motion of particles in fluid is the most common form of collective behavior in physical and biological systems. Here, we demonstrate through both experiment and numerical simulation that the movement of vortices in a rotating turbulent convective flow resembles that of inertial Brownian particles, i.e., they initially move ballistically and then diffusively after certain critical time. Moreover, the transition from ballistic to diffusive behaviors is direct, as predicted by Langevin, without first going through the hydrodynamic memory regime. The transitional timescale and the diffusivity of the vortices can be collapsed excellently onto a master curve for all explored parameters. In the spatial domain, however, the vortices exhibit organized structures, as if they are performing tethered random motion. Our results imply that the convective vortices have inertia-induced memory such that their short-term movement can be predicted and their motion can be well described in the framework of Brownian motions.

Magnetic field sweep rate influence on the critical current capabilities of a Fe(Se,Te) crystal

The relaxation phenomena of a FeSe0.5Te0.5 single crystal sample, with twinned morphology, exhibiting a second magnetization peak effect have been analyzed by means of dc magnetization measurements as a function of magnetic field (H). Using different magnetic field sweep rates for performing the superconducting hysteresis loops m(H), a change in the width of these curves has been observed together with a shift of the second peak field position. A consequent and significant variation of critical current density Jc has been extracted from the superconducting m(H) curves within the Bean critical state model. In this framework, the ratio between the critical current densities Jc calculated at 200 Oe/s and 5 Oe/s has been calculated showing interesting results in terms of transport capabilities. From the Jc(H) curves at T = 10 K for different sweep rates, the irreversibility field has been obtained for T = 10 K and fitted with a power law. The increasing trend of the irreversibility field as a function of sweep rate could suggest the use of this material for power applications where overheating due to vortices movement inside the superconductor has to be limited.