Vortex Movement Research Articles

Investigation study on the flow-induced noise by winglet and shroud shape of an axial flow fan at an outdoor unit of air conditioner

Axial flow fans of outdoor units are equipped with specially shaped winglets and shroud for reduction of the flow-induced noise. In this study, the unsteady state flow field and the characteristics of the flow-induced noise according to the application of the sweptback tip winglets and 30 % covered shroud in an axial flow fan of an outdoor unit of air conditioner were experimentally and numerically analyzed. To analyze the unsteady flow field, large eddy simulation (LES) reflecting the geometry of complicated outdoor unit was performed; and the LES results were used by simplified Ffowcs Williams and Hawkings (FW-H) equation in order to calculate the noise numerically. As a result, asymmetric flow characteristics inside the outdoor unit by the mount and the shape of blade tip and shroud were found to cause inconsistent movement of the tip leakage vortex, which was revealed to change the characteristics of the flow-induced noise.

Vortex motion of a continuous medium depending on the pressure change

Abstract In this paper, we study the vortex motion of a continuous medium, which is described by forces obtained from the principle of least action. It is shown that in a continuous medium the vortex force components are proportional to the velocity and pressure gradient components. This article gives a description of the 2D vortex motion of air in zones of high and low pressure. If the pressure decreases, the angular velocity of rotation of the continuous medium increases, whereas if the pressure increases, the angular velocity fades. The lifting force is obtained due to the vortex movement of air in the form of a funnel. It is shown that the vortex force contains a vortex term of the Euler hydrodynamic equations with a relative factor equal to the velocity of the continuous medium squared divided by the sound velocity squared. To describe the motion of a continuous medium correctly it is necessary to replace the forces obtained by Euler with the forces obtained from the minimum of action in the equations of motion. It is concluded that vortex motions and turbulence are described by the obtained equations of motion, and not by the Navier–Stokes equations. Most likely, this is related to the Problem of the Millennium description of turbulence announced at the International Congress of Mathematics in 2000.

Dynamics of co-rotating vortices in a flow around a bio-inspired corrugated airfoil

Bio-inspired corrugated airfoils show favourable aerodynamic characteristics such as high coefficient of lift and delayed stall at low Reynolds numbers. Two-dimensional (2D) direct numerical simulation has been performed here on a corrugated airfoil at various angles of attack (0°, +5°, -5°) and Reynolds number of 280 to 6700. The objective is to analyse the pressure variation inside the corrugations and correlate it to the vortex movement across the corrugations and the overall aerodynamic characteristics of the corrugated airfoil. The flow characteristics have been examined based on the local Strouhal numbers in the corrugations of the airfoil. It is observed that the pressure variation in each corrugation is the result of vortex merging and separation in the corrugation which plays a major role in changing the flow characteristics. The Strouhal number of the flow is dictated by the most dominant local Strouhal number. The numerical results are further compared with experimental results obtained using particle image velocimetry, and the two set of results are found to match well. These results are significant because they elucidate the effect of corrugation, angle of attack, and Reynolds number on flow over a corrugated airfoil.

Guided Vortex Motion Control in Superconducting Thin Films by Sawtooth Ion Surface Modification.

Design of flux profile and guided motion of magnetic flux quanta (also known as vortices) are central issues for functionality of superconducting devices. Anchoring vortex movement by trapping flux lines through the use of defects and preventing vortex entry by shielding magnetic field have been broadly explored, which can also enable reduction of noise for optimal device operation. Removing vortices entirely via the so-called ratchet effect (employing an asymmetric energy potential) is another alternative. This ratcheting potential is also used in DNA splitting, particle separation, surface atom electromigration, and electrophoresis. Utilizing a superconductor with the ratchet vortex pinning potential induces a dominant motion direction, which can be used to pump flux out from device functional zones. In this work, a varying thickness superconductor with its tailored intrinsic pinning mechanism has been simulated and proven to provide this preferential vortex motion. We demonstrate both theoretically and experimentally that a varying thickness superconducting ratchet is indeed possible. Furthermore, the sawtooth shape of the bridge provides a tunability to the preferred vortex motion direction, dependent on the ramp gradient and intrinsic pinning strength.

Experimental study of the effect of ambient pressure on oscillating behavior of pool fires

Pool fires are known to exhibit self-sustained oscillatory behavior, which plays an important role in the understanding of flame and fire spreading. To investigate the effect of ambient pressure on oscillating behavior of pool fires, the ethanol pool fires with diameters from 2 to 10 cm were conducted under a wide range of pressure from 0.6 to 2.5 atm, where different pressure environments were achieved and maintained using a closed high pressure chamber. Based on the momentum conservation equation for the gas movement driven by buoyant force, the Gr number was derived to illustrate the change of flame structure and oscillation frequency. The results show that the Gr number could explain the flame structure changing from laminar to turbulent. The oscillation intensity, which was redefined using the probability contour of the flame, could be related with Grashof. Furthermore, it was noticed that the influence of ambient pressure and gravity on oscillation frequency depends on the different oscillation mechanisms. Based on the one-dimensional movement of vortex along the axis, a theoretical model was proposed to explain the effect of ambient pressure and gravity on frequency, and then the obtained relationship between Strouhal and Grashof was verified by the measured value.

Inferring Surface Flow Velocities in Sediment-Laden Alaskan Rivers from Optical Image Sequences Acquired from a Helicopter

The remote, inaccessible location of many rivers in Alaska creates a compelling need for remote sensing approaches to streamflow monitoring. Motivated by this objective, we evaluated the potential to infer flow velocities from optical image sequences acquired from a helicopter deployed above two large, sediment-laden rivers. Rather than artificial seeding, we used an ensemble correlation particle image velocimetry (PIV) algorithm to track the movement of boil vortices that upwell suspended sediment and produce a visible contrast at the water surface. This study introduced a general, modular workflow for image preparation (stabilization and geo-referencing), preprocessing (filtering and contrast enhancement), analysis (PIV), and postprocessing (scaling PIV output and assessing accuracy via comparison to field measurements). Applying this method to images acquired with a digital mapping camera and an inexpensive video camera highlighted the importance of image enhancement and the need to resample the data to an appropriate, coarser pixel size and a lower frame rate. We also developed a Parameter Optimization for PIV (POP) framework to guide selection of the interrogation area (IA) and frame rate for a particular application. POP results indicated that the performance of the PIV algorithm was highly robust and that relatively large IAs (64–320 pixels) and modest frame rates (0.5–2 Hz) yielded strong agreement ( R 2 > 0.9 ) between remotely sensed velocities and field measurements. Similarly, analysis of the sensitivity of PIV accuracy to image sequence duration showed that dwell times as short as 16 s would be sufficient at a frame rate of 1 Hz and could be cut in half if the frame rate were doubled. The results of this investigation indicate that helicopter-based remote sensing of velocities in sediment-laden rivers could contribute to noncontact streamgaging programs and enable reach-scale mapping of flow fields.

Алгоритм движения точечных вихрей в ограниченной области

The problem of calculating the paths of motion of a set of point vortices in an ideal incompressible liquid in a limited area is considered. The area is supposed to be piecewise smooth. The stream function at any given time is presented as a sum: the stream functions of point vortices and the potential of a simple layer, the density of which - the density of vortexes on the border - is required to determine. Regardless of time, the stream function harmoniously extends into the exterior of the area and is identically equal to a constant at the boundary, and, therefore, is a Roben potential. Briefly, the paper describes an algorithm for calculating the Roben potential. The unknown density of vortices is sought in the form of a linear combination of a complete system of potentials, and the coefficients are determined by the values of the Roben potential, as a solution to the inverse problem; determination of the coefficients reduces to solving a system of linear equations with a Gram matrix for a linearly independent system of functions. By the function of stream by tangents determine the trajectories of movements of vortices. The results of computational experiments of the motion of several point vortices in a square are presented. A computer analysis of the movement was carried out: two, four and eight point vortices, calculated the trajectories of their movement and found stationary and periodic, stable and unstable configurations.

Unsteady Effects of Upstream Nozzle Wakes on Hub-Endwall Flow and Heat Transfer of an HPT Rotor

Nozzle wakes have significant effects on the heat transfer on the rotor blade and endwall surfaces. Numerical studies have been carried out in a subsonic high pressure turbine stage to investigate the rotor’s secondary flow field and endwall heat transfer. Both steady and unsteady RANS analyses were accomplished for the multiple blade rows using mixing-plane and domain-scaling techniques respectively. Special attention was focused on the particular nozzle wake structure of secondary passage vortex near the hub endwall and its effects on the endwall heat transfer characteristics. Unsteady solution indicates that the passage vortex near the rotor hub is transported toward the midspan due to the blade interaction and rotation effects. In the front passage region, the time-averaged result yields higher heat transfer up to 20% than a steady one, and the transient fluctuation amplitude reaches 40% of mean values along the passage vortex moving path. In the rear passage region, the difference between steady and unsteady solutions is negligible. Current study reveals that the major difference of wake effects between an actual turbine and a linear cascade with moving bars comes from the movement of the vortical endwall passage vortex in the incoming flow.

EFD and CFD Study of Forces, Ship Motions, and Flow Field for KRISO Container Ship Model in Waves

Ship motion responses and added resistance in waves have been predicted by a wide variety of computational tools. However, validation of the computational flow field still remains a challenge. In the previous study, the flow field around the Korea Research Institute for Ships and Ocean Engineering (KRISO) Very Large Crude-oil Carrier 2 tanker model with and without propeller condition and without rudder condition was measured by the authors, as well as the resistance and self-propulsion tests in waves. In this study, the KRISO container ship model appended with a rudder was used for the higher Froude number .26 and smaller block coefficient .65. The experiments were conducted in the Osaka University towing tank using a 3.2-m-long ship model for resistance and self-propulsion tests in waves. Viscous flow simulation was performed by using CFDShip-Iowa. The wave conditions proposed in Computational Fluid Dynamics (CFD) Workshop 2015 were considered, i.e., the wave-ship length ratio λ/L = .65, .85, 1.15, 1.37, 1.95, and calm water. The objective of this study was to validate CFD results by Experimental Fluid Dynamics (EFD) data for ship vertical motions, added resistance, and wake flow field. The detailed flow field for nominal wake and self-propulsion condition will be analyzed for λ/L = .65, 1.15, 1.37, and calm water. Furthermore, bilge vortex movement and boundary layer development on propeller plane, propeller thrust, and wake factor oscillation in waves will be studied.

Dominant factors for the pinning enhancement by large artificial partial and complete antidots in superconducting films

Partially (blind) or fully perforated antidots (BADs or ADs, respectively) fabricated by laser lithography and ion beam etching in superconducting YBa2Cu3O7 (YBCO) films possess a cumulative circumference wall surface, which is found to be responsible for pinning vortices and/or magnetic flux, whereby increasing the critical current density (Jc) relative to corresponding plain (unpatterned) films. Using a variety of contrastingly shaped, relatively large 2–5 μm BADs and ADs, the Jc of YBCO thin films has been effectively increased within the relatively narrow band of wall surfaces of antidots, independent whether patterns are AD or BAD type. Independence of antidot types indicates that enhancement is insensitive whether magnetic flux is inside the ADs, or vortices are inside the BADs. Within this AD wall surface band region a clear shape dependence also emerges. This finding may also provide a guide for superconducting devices requiring maximal Jc and reduced associated vortex movement noise.

Improving flashing light frequency and CO2 fixation rate with vortex movement of algal cells in raceway pond with conic baffles

The inefficiency of the flashing light effect is one of the major obstacles to CO2 fixation by microalgae. To improve the flashing light frequency of Chlorella vulgaris in a raceway pond with alternatively permutated conic baffles (RWP-APCB), the detailed vortex structures of algal cell movement were clarified and optimised. Numerical simulation results showed that the peak vortex intensity occurred in the centre of the APCB, whereas the peak solution velocity occurred in the middle of the baffle spacing. The vortex diameter was mainly affected by the relative spacing of the conic baffles, whereas the vortex centre was mainly affected by their relative height. Optimisation of the relative height and spacing of the RWP-APCB doubled the flashing light frequency of algal cells and increased the light fraction during the light/dark cycle by a factor of 3.1. The CO2 fixation rate of the algal biomass in the RWP-APCB increased by 18.1–3.8 g/L/d.

Downstream interference effect of low-Scruton-number high-rise buildings under turbulent boundary layer flow

This paper investigates the variation of root-mean-square values of acceleration responses and corresponding aerodynamic dampings of two square cross-sectional high-rise buildings with low Scruton numbers due to interference effects caused by neighboring identical buildings. Aero-elastic vibration test is adopted for displacement and acceleration measurements of a rigid, base-pivoted aero-elastic principal building model by a two-directional sway gimbal system. The principal building is manufactured in the shape of a square prism model with an aspect ratio of eight. Twenty close interference locations are of interest, with a special focus on the across-wind responses. Results show that the variations of interfered acceleration responses and estimated damping ratios exhibit different tendencies for different interference locations at different reduced velocities. For the typical upstream interfered effect, the interfering building located at the oblique-upwind locations in this study, the acceleration response with lower Scruton number is suppressed at lower reduced velocities and is amplified at higher reduced velocities. On the other hand, for the secondary downstream interference effect, i.e., the interfering building located at downwind locations, the amplification or reduction in acceleration response is less sensitive to Scruton number but is related to the gap between two buildings. The corresponding response spectra and resultant damping ratios are then calculated to enhance the understanding of different interference mechanisms. Finally, an idealized two-dimensional CFD simulation technique is adopted to further explain the differences between the upstream and downstream interference mechanisms from the viewpoint of the vortex movement between two buildings.

Theoretical Analyses of the Number of Backflow Vortices on an Axial Pump or Compressor

Abstract Backflow vortices occasionally occur in the annular mixing zone between the main and axially reverse whirling flows from the impeller tip clearance on an axial pump or compressor. A number (N) of tornado-like backflow vortices rotate around themselves and revolve around the casing axis with a diameter (d) and a revolving angular velocity (ω). To investigate the factors determining N and the movement of the backflow vortices, theoretical analyses are performed. Each backflow vortex is generated in the mixing zone; the core region of each backflow vortex is considered to be a forced vortex, while the outer region is considered to be a free vortex. The ratio (f) of the forced vortex to the distance between the backflow-vortex center and the casing is defined. Each backflow vortex has a circulation and induces movements of all the other backflow vortices depending on the distance between the vortices. The casing restricts the movements of all the backflow vortices, and imaginary image vortices are considered on the other side of the casing. Consequently, for d, ω, N, and f, any parameter can be determined if the other three parameters are specified. As an application of the present theory to an inducer representing an axial pump or compressor, the number (Ncav) of “backflow-vortex cavitations,” which occur around the backflow-vortex center, is predicted. Cavitation is visible; therefore, Ncav is quantitatively measurable. In the parameter ranges studied for the tested inducer, the predicted value of N accurately agrees with the experimentally measured value of Ncav.

Interaction between separation bubble and impinging vortices over a finite blunt plate

In this work, the interactive process between separation bubble and impinging leading-edge vortices, which is superimposed in unsteady separated and reattaching flows over a finite blunt plate, was experimentally determined. We used an effective recognition strategy based on an offline data analysis by dynamic mode decomposition (DMD) and online DMD computation in a field-programmable gate array (FPGA). The approach was established for phase-locking particle image velocimetry (PIV) measurements of the underlying vortex dynamics. The DMD mode coefficients of wall-pressure fluctuations following the temporal evolution of the corresponding unsteady events clearly reflected the interactive process, in which three consecutive impinging vortices appeared in one period of the separation bubble. The global interactive process between the separation bubble and the impinging vortices was classified into three consecutive processes: an amplification process, a transition process and a preparation process. The phase-averaged PIV measurements revealed the following: (a) During the amplification process, the separation bubble and impinging vortices are in a synchronous enlargement process beginning from the shortest position of the separation bubble atx/D=3.00. (b) In both the transition and preparation processes, the interaction was characterized by a flapping separation bubble (which enlarged in the first half of the period and then shrank in the second half of the period) and by the impinging vortices constantly shedding to the downstream region. Finally, the underlying shear layer instabilities and vortex movements of these three interactive processes were analyzed.

Low-frequency flexural wave based microparticle manipulation.

Manipulation of microparticles and bio-samples is a critical task in many research and clinical settings. Recently, acoustic based methods have garnered significant attention due to their relatively simple designs, and biocompatible and precise manipulation of small objects. Herein, we introduce a flexural wave based acoustofluidic manipulation platform that utilizes low-frequency (4-6 kHz) commercial buzzers to achieve dynamic particle concentration and translation in an open fluid well. The device has two primary modes of functionality, wherein particles can be concentrated in pressure nodes that are present on the bottom surface of the device, or particles can be trapped and manipulated in streaming vortices within the fluid domain; both of these functions result from flexural mode vibrations that travel from the transducers throughout the device. Throughout our research, we numerically and experimentally explored the wave patterns generated within the device, investigated the particle concentration phenomenon, and utilized a phase difference between the two transducers to achieve precision movement of fluid vortices and the entrapped particle clusters. With its simple, low-cost nature and open fluidic chamber design, this platform can be useful in many biological, biochemical, and biomedical applications, such as tumor spheroid generation and culture, as well as the manipulation of embryos.

Flux vortex dynamics in type-II superconductors

The flux-pinning landscape in type-II superconductors determines the response of the flux line lattice to changing magnetic fields. Typically, the flux vortex behaviour is hysteretic and well described within the framework of the Bean critical-state model and its extensions. However, if the changing magnetic field does not move the flux vortices from their pinning sites, their response remains linear and reversible. The vortex displacement, then, is characterised by the Campbell penetration depth, which itself is related directly to the effective size of the pinning potential. Here, we present measurements of the Campbell penetration depth (and the effective size of the pinning potential) as a function of magnetic field in a single-grain bulk GdBa2Cu3O superconductor using a pick-up coil method. Hence, the hysteretic losses, which take into account the reversible vortex movement, are established.

Experimental investigation of vortex ring formation as a consequence of spiral vortex re-connection

The unsteady shape variation of a cavitating spiral vortex is experimentally studied pointing out the repetitive creation of vortex ring (or vortex loop). To generate the spiral vortex structure, a newly designed vortex generator is employed. This generator is used to study the decelerated swirling flow leading to the spiral vortex formation as a consequence of spiral vortex breakdown, which is considered to be the main triggering mechanism for the occurrence of the coherent vortex rope structure in the Francis turbine draft tube operated at part load conditions. Thanks to its design, the vortex generator enables to change the ratio between fluxes of axial momentum and tangential moment of momentum of generated swirl. Using this set-up, the behavior of the vortex structure changes in a similar way as the flow rate variation in the draft tube of Francis turbine. At certain flow conditions, the spiral vortex movement is characterized by sudden spiral entanglement leading to disconnection of a vortex ring and followed by spiral reconnection. Thanks to the transparent diffuser of the swirl generator apparatus, both high-speed camera recording of the cavitating vortex and PIV measurements of velocity fields at cavitationfree conditions are employed. The main aim of this paper is to link the visual observation of the above described vortex dynamics with the velocity fields measured in one longitudinal and one cross-sectional planes.

О РОЛИ МЕЗОМАСШТАБНЫХ ВИХРЕЙ В ПЕРЕМЕЩЕНИИ ПЯТЕН НЕФТЕПРОДУКТОВ В ЮГО-ВОСТОЧНОЙ БАЛТИКЕ (СПУТНИКОВАЯ ИНФОРМАЦИЯ)

In this paper, on the basis of an analysis of the successive satellite optical images (MODISAqua, TIRS Landsat-8, AVHRR NOAA-18) and radar images (SAR-C Sentinel-1A, SAR-C Radarsat-2) on June 8–11, 2015, the effect of the mesoscale vortex movement (anticyclone with diameter of 35 km and associated cyclone) on the transport of oil spots in the northern part of the Gdansk Bay was demonstrated for the first time. The velocities of this transport are estimated; the observed picture of the movement of the spots is compared with their transfer according to the Seatrack Web model. The largest (about 20 cm/s) drift velocity corresponded to the spot that appeared near the periphery of the anticyclonic vortex (the region of maximum velocities), the smallest one was at the spot near the center of the vortex. At a wind speed of not more than 5 m/s on June 10 and an assumed orbital velocity of the anticyclone of the order of 20 cm/s, the contribution of the vortex motion to the total transport of the spots under the influence of wind and vortex should be decisive. The observed drift of the spots did not correspond to the forecast of their movement by the Seatrack Web numerical model, which did not take into account the vortex dynamics of the waters.

Compressible Navier-Stokes Equations in Cylindrical Passages and General Dynamics of Surfaces—(I)-Flow Structures and (II)-Analyzing Biomembranes under Static and Dynamic Conditions

A new approach to solve the compressible Navier-Stokes equations in cylindrical co-ordinates using Geometric Algebra is proposed. This work was recently initiated by corresponding author of this current work, and in contrast due to a now complete geometrical analysis, particularly, two dimensionless parameters are now introduced whose correct definition depends on the scaling invariance of the N-S equations and the one parameter δ defines an equation in density which can be solved for in the tube, and a geometric Variational Calculus approach showing that the total energy of an existing wave vortex in the tube is made up of kinetic energy by vortex movement and internal energy produced by the friction against the wall of the tube. Density of a flowing gas or vapour varies along the length of the tube due to frictional losses along the tube implying that there is a pressure loss and a corresponding density decrease. After reducing the N-S equations to a single PDE, it is here proven that a Hunter-Saxton wave vortex exists along the wall of the tube due to a vorticity argument. The reduced problem shows finite-time blowup as the two parameters δ and α approach zero. A rearranged form for density is valid for δ approaching infinity for the case of incompressible flow proving positive for the existence of smooth solutions to the cylindrical Navier-Stokes equations. Finally we propose a CMS (Calculus of Moving Surfaces)–invariant variational calculus to analyze general dynamic surfaces of Riemannian 2-Manifolds in R 3 . Establishing fluid structures in general compressible flows and analyzing membranes in such flows for example flows with dynamic membranes immersed in fluid (vapour or gas) with vorticity as, for example, in the lungs there can prove to be a strong connection between fluid and solid mechanics.

Experimental Study on Gas-Solid Flow in the Spouted Bed under Longitudinal Vortex Effect.

To strengthen the particles radial movement and mixing, the longitudinal vortex generator of a sphere was adopted in the spouted bed in this study. To find the influence of the longitudinal vortex and particle properties on axial and radial velocities of particles in a 152 mm-diametered spouted bed, particle image velocimetry (PIV) was employed. The experimental results show that the addition of the longitudinal vortex generator caused the vortex movement of high-speed gas and induced a considerable secondary fine vortex in the cross section of the spouted bed, and the existence of longitudinal vortex significantly improved the radial velocity of particles, compared with that of the conventional spouted bed. Due to the effect of longitudinal vortex on particles, the phenomenon of early dropping of particles was increasingly obvious with the rise in bed height, and the value of axial velocity of particle phase was negative. With the decrease in the particle diameter, the longitudinal vortex effect of gas-driven particle movement would be enhanced. The longitudinal vortex could enhance particle velocity under a wide range of particle diameters, and the enhancement factor η decreased with the rise in the particle diameter and gradually approaches to 1.