Vortex Rotation Research Articles

Reynolds number effects on swirling flows intensity and reattachment length over a backward-facing step geometry using STD k-ε turbulence model

Swirling flow at recirculation zone of backward-facing step (BFS) geometry undoubtly affected by Reynolds number since it is involving rotational vortices. This flow behavior can be represented by flow intensity and reattachment length inside the geometry. BFS geometry is chosen for it is well-known characteristics visualizing swiriling flow that occur in many industrial application. Unfortunately, experimental method for visualizing rotational vortices over a BFS geometry oftenly involve advance technology including the image capturing devices. CFD method is use in this research for computionally visualize respected flows with Reynolds number variation with lower cost. The model is 3 dimensional with Step height (h) = 41mm, upstream height (H) = 81mm, expansion ratio = 1.5, total length (L) = 4050 mm and width = 20h. The mesh is triangular with 90.293 nodes. Reynolds numbers varied to Re = 4290.39; 6673.94; 7614.23; and 9287.29 which gained from experimental data. The working fluid is single phase air, with inlet and outlet temperature also gained from experimental data. The initial fluid temperature at inlet and outlet are 28.4°C and 28.8°C; 27.3°C and 28.6°C; 26.2°C and 28.3°C; 28.7°C and 29.8°C for respected Reynolds number variation. The flow condition is assumed transient with time step set of 1 and simulation is done with STD k-ε turbulence model. Highest Reynolds number variation reattached at reattachment / step height X/h = 6.82, compared to Re = 4290.39 with X/h = 11.71. CFD simulation results show that eddies inside the vortices and the X/h affected by floe velocity and so on with the flow temperature.

Unveiling the magnetic nature of chromospheric vortices

Context. Vortex structures in the Sun’s chromosphere are believed to channel energy between different layers of the solar atmosphere. Aims. We investigate the nature and dynamics of two small-scale quiet-Sun rotating structures in the chromosphere. Methods. We analysed two chromospheric structures that show clear rotational patterns in spectropolarimetric observations taken with the Interferometric Bidimensional Spectrometer at the Ca II 8542 Å line. Results. We present the detection of spectropolarimetric signals that manifest the magnetic nature of rotating structures in the chromosphere. Our observations show two long-lived structures of plasma that each rotate clockwise inside a 10 arcsec2 quiet-Sun region. Their circular polarisation signals are five to ten times above the noise level. Line-of-sight Doppler velocity and horizontal velocity maps from the observations reveal clear plasma flows at and around the two structures. A magnetohydrodynamics simulation shows these two structures are plausibly magnetically connected. Wave analysis suggests that the observed rotational vortex pattern could be due to a combination of slow actual rotation and a faster azimuthal phase speed pattern of a magnetoacoustic mode. Conclusions. Our results imply that the vortex structures observed in the Sun’s chromosphere are magnetic in nature and that they can be connected locally through the chromosphere

About a possible derivation of the London equations

In continuation of some previous work published by this author in an open access journal [S. Koutandos, IOSR J. Appl. Phys. 10, 26 (2018); 10, 35 (2018); 9, 47 (2017); 11, 72 (2019)], he now derives the London equations from an expansion of the rotation of vorticity. Vorticity is a vector quantity described in fluid mechanics which characterizes the angular motion of a point particle as it moves. A small ball, for example, found in a field of vorticity would turn around itself. This is in accordance with the existence of the spin of a particle. We claim that due to the dipolar nature of the electric charge, its rotation vortex effects appear. It is found that the total time derivative of the radius possibly due to Brownian motion is different from the velocity but is used as a starting point in describing a fluid-like flow for the electron where all the quantities behave accordingly. Finally, we ascribe the relativistic radius of the electron to a curvature of spacetime from the mass energy equivalence for the electric energy. This paper may also be looked at as one more discussion about the hidden variables quest in quantum mechanics, offering some progress in understanding them.

Experimental research of single - rotor helicopter unintentional yaw rotation

Aviation accidents related to unintentional rotation may periodically occur while flying single-rotor helicopters. On-time and correct actions may help the pilot to find the way out of this hazardous situation. But it is also important to understand the situation which contributes to the unanticipated yaw occurrence, and whether there are any factors which can stop the pilot from preventing such unintentional rotation, in order to avoid these conditions. Literature analysis shows that researchers studying this phenomenon don’t have the shared vision on unanticipated yaw occurrence conditions. In regards to this fact the decision to carry out a series of wind tunnel experiments using helicopter model and propeller was taken. The main object of research was a radio-controlled model of the Blade 130 x helicopter, mounted on a platform rotating around a vertical axis, which was installed on a vertical strut. Research-laboratory aerodynamic complex belonging to the Aerodynamics, Design and Aircraft Strength Chair of Moscow State Technical University of Civil Aviation was used to generate airflow. A set of dynamic experiments was carried out to determine the conditions contributing to unanticipated yaw occurrence. The analysis of the experiments has shown that there is a range of sliding angles at a certain speed of the incoming air flow which makes the helicopter yaw balancing impossible, and if the helicopter occasionally gets into this range, it inevitably leads to the unintended rotation of the helicopter on the yaw occurrence. Helicopter yaw trim inability occurs at negative sideslip angles because of tail rotor thrust decrease due to the incoming airflow blowing which decreases the blades angles of attack and worsens helicopter airframe aerodynamic moment that coincides in direction with main rotor torque if helicopter airframe possesses directional stability. In these conditions the required tail rotor pitch is greater than the available pitch so the pilot is not able to counteract the initiated unanticipated yaw rotation of the helicopter that has begun. The possibility of helicopter unanticipated yaw rotation caused by the impact of the main rotor on the tail rotor was not experimentally confirmed. It was impossible to create the conditions of unanticipated yaw occurrence during the experiments because of the tail rotor vortex ring state.

Liutex theoretical system and six core elements of vortex identification

The third-generation vortex identification method of Liutex (previously called Rortex) was introduced by the team led by Prof. Chaoqun Liu from University of Texas at Arlington to mathematically extract the rigid rotation part from the fluid motion, and thus to define and visualize vortices. Unlike the vorticity-based first generation and the scalar-valued second generation, Q, λ2, Δ and λci methods for example, the Liutex vector provides a unique, mathematical and systematic way to define vortices and visualize vortical structures from multiple perspectives without ambiguity. In this article, we summarize the recent developments of the Liutex framework and discuss the Liutex theoretical system including its existence, uniqueness, stability, Galilean invariance, locality and globality, decomposition in tensor and vector forms, Liutex similarity in turbulence, and multiple Liutex-based vortex visualization methods including Liutex lines, Liutex magnitude iso-surfaces, Liutex-Ω method, and Liutex core line method, etc.. Thereafter, the six core elements of vortex identification, including (1) absolute strength, (2) relative strength, (3) local rotational axis, (4) vortex rotation axes, (5) vortex core size, (6) vortex boundary, are used as touchstones against which the Liutex vortex identification system is examined. It is demonstrated with illustrative examples that the Liutex system is able to give complete and precise information of all six core elements in contrast to the failure and inaccuracy of the first and second-generation methods. The important concept that vorticity cannot represent vortex and the superiority of the Liutex system over previous methods are reiterated and stated in appropriate places throughout the paper. Finally, the article concludes with future perspectives, especially the application of the Liutex system in studying turbulence mechanisms encouraged by the discovery of Liutex similarity law. As a newly defined physical quantity, Liutex may open a door for quantified vortex and turbulence research including Liutex (vortex) dynamics and lead the community out of the shadow of turbulence research which traditionally relies on observations, graphics, assumptions, hypotheses, and other qualitative analyses. An optimistic projection is that the Liutex system could be critical to investigation of the vortex dynamics in applications from hydrodynamics, aerodynamics, oceanography, meteorology, etc. and to research of the generation, sustenance, modelling and controlling of turbulence.

Vortex pairs in the discrete nonlinear Schrödinger equation

The aim of the present work is to examine the role of discreteness in the interaction of both co-winding and counter-winding vortices in the context of the nonlinear Schrödinger equation. Contrary to the well-known rotation of same charge vortices and translation of opposite charge vortices, we find that strong discreteness is able to halt both types of pairs into stationary, potentially stable configurations up to a critical inter-site coupling strength. Past the relevant critical point the behavior is also somewhat counter-intuitive as, for instance, counterwinding vortices start moving but also approach each other. This lateral motion becomes weaker as the continuum limit is approached and we conjecture that genuine traveling appears only at the continuum limit. Analogous features arise in the cowinding where the discrete coherent structure pair spirals outward, with rigid rotation being restored only in the continuum limit.

Optical vortex rotation and propagation from a spiral phase plate resonator with surface reflective coating.

A spiral phase plate resonator (SPPR) is created by depositing a reflective coating on the surfaces of a single conventional spiral phase plate (SPP) for the first time to the best of our knowledge. Optical transmission through the SPPR on the output plane of the device is measured to give sharp Fabry-Perot resonances as a function of beam roll angle. Similar measurements are performed for the reflected light emerging from the input plane of the SPPR device. Varying the light frequency going into the SPPR changes the orientation of the angular pattern (Fabry-Perot resonances) to give the rotational constant of the device, in agreement with theory. The optical mode profile is measured after the beam has propagated beyond the plane of the SPPR device while remaining in the diffraction near field, thus revealing new features in the transmitted optical beam. These new results have important implications for developing the SPPR for microscopy, imaging, angle measurement, rotational scanning, and LiDAR.

A method of evaluating the vortex rope strength in draft tube of Francis turbine

A precessing vortex core in the draft tube of Francis turbine is considered as unstable flow conditions and the cause of many undesirable system instabilities for hydraulic power stations. The feature of vortex rope, pressure fluctuations and runner outlet velocity at part-load conditions are investigated experimentally and numerically in this paper. An obvious vortex rope could be observed at 0.88Q11BEP point and produces the most intensive periodic pressure fluctuation at the vortex rotation frequency fv along the whole passage of Francis turbine. At other conditions away from this point, the vortex rope becomes unobvious or even invisible, and the associated pressure fluctuation amplitude also reduces. This trend could be well represented by the new parameters G and Vs, which could be used to determine the strength of helical vortex field based on the gradient of time-averaged velocity on horizontal section of the draft tube cone. Transient simulations using VLES turbulence model could obtain satisfying results by comparing with experimental data, especially in terms of the time-averaged axial velocity profile resolution. Therefore, this new method enables the designers to evaluate vortex strength in engineering applications.

BVI-noise generation by wing-shaped helicopter blade

Aerodynamic noise includes a number of noise components, among which rotational noise and vortex noise (BVI-noise) make the largest contribution to the overall noise generated. Rotation noise depends on the magnitude of the velocity of the incoming blade and prevails over other noise components at significant Mach Mach numbers. Unlike rotation noise, vortex noise is evident at low helicopter flight speeds, moderate Mach numbers. In the formation of this type of noise,an important role is played by the longitudinal geometry. Therefore, recently the shape of the helicopter blade is chosen close to existing natural forms, which are as balanced as possible. One of these may be a wing-shaped blade. In this work, the problem of generating BVI noise by the wing shaped blade of a helicopter is posed and solved. The mathematical model of the problem is constructed on the previously proposed by the author and successfully tested system of aeroacoustic equations for the general case. Estimated features in this system are pulsations of sound pressure and sound potential. The calculated data of these quantities, as well as their derivatives, were used to study near and far sound fields. In particular, the dependence of the density ripple distribution is revealed from the blade geometry, the angle of attack and the blade angle to the oncoming flow. Increasing flow velocity contributes to the emergence of transverse ripples on the surface blades that dominate the longitudinal ripples by level. An interesting feature noticed in the calculations is that there are calculations for moderate Mach numbers M=0.2,0.3 situations, at certain angles of blade placement to the stream and angles of attack where rotation noise dominates eddy noise. For values Mach numbers M>0.4 rotation noise plays a major role in blade noise generation. The noise level generated is in the range 50dB≤L≤60dB, which is lower by 5-6dB for the Blue Edge blade, as well as the rounded blade. In addition, activation of the high-frequency region in the frequency spectrum of noise was observed f≈840Hz. The results of the calculations show that the blade of the wing-shaped is low-noise in the mode of maneuvers at small flight speeds.

Technology of Measuring Air Parameters Aboard the Single-Rotor Helicopter Using a Fixed Multifunctional Receiver

The technology is revealed for measuring air parameters aboard the single-rotor helicopter using the information of the aerodynamic field of a main rotor vortex column perceived by a fixed multifunctional receiver made as a two-channel scheme with an ion-mark and aerometric channels. The algorithms of forming and processing the information, technical characteristics of the system obtained by the results of the study of experimental samples in the wind tunnel are given.

Rotation of dust vortex in a metal saw structure in dusty plasma

By designing a metal saw structure, both negative and positive rotations of dust vortices are obtained experimentally. With increasing gas pressure, the dust vortex undergoes different spatial distribution from dense dust cloud to dust void, then to dust chain. The transition between the negative and positive rotations of dust vortices is reversible and controllable by changing the gas pressure/input power. The underlying mechanism of this transition is preliminarily explored.

GPU-accelerated transient lattice Boltzmann simulation of bubble column reactors

Design parameters for Bubble Column Reactors such as backmixing and light/dark cycles of microalgae cells are pertinent to transient flow dynamics and mesoscale coherent structures. Transient simulation is therefore of practical significance. Traditional CFD solvers are generally implemented on multi-core CPU workstations, which is time-consuming and difficult to meet the requirement of industry applications. We developed a GPU-accelerated transient LBM simulation of gas-liquid flow, achieving 5000 times acceleration in comparison with the CFD simulation. A notable feature of this method, which allows a tunable and smaller dimensionless relaxation time, is the remarkable decrease of required mesh number in LBM simulation by several orders of magnitude. The solver is validated against experimental data, resolving two mechanisms of mesoscale structure, i.e., vortex rotation and radial migration, in the intensification of macromixing. The computation acceleration and resolution of mesoscale structures demonstrate the potential of this approach for fast simulation of industrial applications.

Алгоритм оценки ротора векторных полей движений земной поверхности по геодезическим данным

According to the changes of geodetic elements (coordinates, heights, directions) after multiple measurements, it is possible to represent the field of geodetic points’ displacement vector. When studying the stress-strain state of the earth’s surface, the vectors obtained can be used not only to calculate the earth’s deformation tensor in the area under study, but also the differential characteristics of the vector field, called divergence and rotor (vortex, curl). The author proposes the way to determinethe rotor according to discrete geodesic observations of displacement vectors on the surface of the surveyed area. The most important continuation of this research work is the method of geodynamic systemsmathematical modeling for predictive purposes. In order to study the complex (nonlinear) geodynamic processes, an appropriate mathematical basis should be chosen. Here the attention is drawn to the attraction of the mathematical foundations of field theory. The variants of the curl definition are proposed – one of the vector fields’ differential characteristics. To assess the characteristics of vector fields when using multiple geodetic measurements, the finite element method can be used. The division of the surveyed area into triangles enables you to determine the characteristics of the deformation after calculating the elements of the strain tensor.

Controllable Synthesis of Silver Nanoparticles Using Piezoelectric-Actuated High-Frequency Vibration Self-Circulating Microfluidic Reactor

Based on the liquid-phase reduction mechanism, a controllable synthesis method, which uses piezoelectric-actuated high-frequency vibration self-circulating microfluidic reactor, to prepare silver nanoparticles is proposed. Firstly, the synthesis mechanism of silver nanoparticles and the working principle of the microfluidic reactor were analyzed. Then, in order to study and explore the influence of self-circulating and high frequency vibration on the synthesis of silver nanoparticles, a series of related synthesis experiments were carried out. The synthesized silver nanoparticles were characterized by UV-Visible spectroscopy and transmission electron microscopy. The effects of micropump driving voltage and high-frequency vibration on the synthesis of silver nanoparticles were analyzed. The experiment results show that when the silver nanoparticles were synthesized using piezoelectric-actuated high-frequency vibration self-circulating microfluidic reactor, the higher the driving voltage of the circulating reflux micropump, the faster the vortex rotation speed in the mixing pool and the more uniform the reagent reaction. Besides, high-frequency vibration can suppress the aggregation of silver nanoparticles, and balance the growth environment of particles, which is beneficial to the formation of silver nanoparticles with good monodispersity, high sphericity and small size deviation.

Performance analysis of multi-stage gravitational water vortex turbine

In this study, the performance of a multi-stage gravitational water vortex turbine (GWVT), which is assembled in a conical basin, is investigated analytically and experimentally. Each runner of the multi-stage GWVT is independent in terms of power generation through telescopic shaft arrangement. Performance parameters, such as rotational speed, torque, power and efficiency, are analyzed under various load conditions in which the effects of design parameters, such as rotors ratio, offset distance between neighbouring runners, and intra-staging and inter-staging of two-stage and three-stage GWVT, are considered. In the multi-stage GWVT, the profile of the blades of upstream runners result in minimal vortex distortion. Thus, the power generation capacity of downstream runners are ultimately enhanced because the performance of latter runners strongly depend on the head utilization capacity of the former runner. Furthermore, the runners with blades tilted on a vertical plane are best suited for the position near the bottom of the basin, whereas cross-flow blades are recommended at the top position. Moreover, the present study suggests that the rotors ratio of the neighbouring runners be selected in such a way that the two runners have the same rotor-to-basin diameter ratio with optimum offset distance. Multi-staging in GWVT demonstrates the development of a combined effect of solid body rotation and free vortex. It also shows a prominent improvement in the overall performance of the turbine compared with that of single-stage GWVT. The proposed mathematical model successfully predicts the experimental results qualitatively and quantitatively, thereby proving its reliability and robustness.

A hyperbolic partial differential equation model for filtering turbulent flows

A two dimensional partial differential equation scheme that uses a second-order hyperbolic diffusion equation for image denoising is developed to a three dimensional model for filtering isotropic turbulence. The mathematical derivation of the model is introduced and a consistent finite difference numerical approximation scheme is proposed. The model is tested against the velocity fields of isotropic turbulence that are simulated by solving the lattice Boltzmann(LB) and the Navier–Stokes(NS) equations, respectively. The D3Q15 LB model and the Fourier spectral method are used to solve the LB equation and the Navier–Stokes vorticity equation at grid points of 2563, respectively. Also the filtering method with the choice of the same filtering parameters is applied against a synthetic turbulent field with the same number of points. The high rotation vortex identification method Q is used to visualize the total, coherent and incoherent fields in all cases of the study. Despite the different nature of the LB and NS direct numerical simulations and the synthetic turbulence, all input parameters for the hyperbolic filtering model are chosen the same in all cases. Comparisons between the LB and NS filtered energy spectra, coherent vortices, incoherent regions, skewness, flatness and the fourth order moments are also considered. The same features are calculated for the non-filtered and filtered synthetic turbulent fields. It is shown that the coherent part preserves all statistical features of turbulence. However, the isotropy is the only feature that has been preserved for the incoherent part and other statistical features are divergent in all cases of the study.

Computer modeling of the vapour vortex orientation changes in the short low- temperature heat pipes

The results of computer studies of the vortex formation and orientation changes inside short heat pipes (HP’s) with profiled vapour channel in the Laval–liked nozzle form are presented. For the first time it was found that the vapour vortex of moist compressible vapour flow in the cooled part of vapour channel changes its rotational motion direction. The rotation direction of the toroidal vapour vortex is dependent on the heat power value, entering to the HP’s evaporator. With low heat power loads (a small temperature head) the rotational direction of the circular toroidal vapour vortex due to the Coanda effect and sticking moving vapour jets to the channel’s walls occurs from the periphery to the longitudinal axis of the vapour channel. While the heat power loads increasing, the direction of the toroidal vapour vortex ring rotation changes to the opposite, from the longitudinal axis to the periphery of the vapour channel. The thickness of the formed working fluid condensate film located under the toroidal vapour vortex also related to the evaporator heat power load and vapour vortex rotation direction. With weak temperature head, the vapour vortex rotates from the walls to the channel center and slow down the movement condensate film on the HP’s top cover surface to the capillary-porous insert, thereby increasing the effective film thickness. As the heat head increases, the vapour vortex rotation direction changes to the opposite one and direction of vapour flow and the liquid condensate film becomes the same, which leads to decrease in the effective film thickness. Experimental results of the condensate film thickness measurements, obtained with capacitive sensors show a sharp decrease in thickness with a temperature head increasing, what could be an indirect confirmation of the vapour vortex rotation direction changes. Numerical method for vapour turbulent flows based on Navier-Stokes (Reynolds) full equation system was used to calculate the moist vapour vortex flow in low-temperature HP’s.

A Liutex based definition and identification of vortex core center lines

Six core issues for vortex definition and identification concern with (1) the absolute strength, (2) the relative strength, (3) the rotational axis, (4) the vortex core center, (5) the vortex core size, and (6) the vortex boundary (Liu C. 2019). However, most of the currently popular vortex identification methods, including the Q criterion, the λ2 criterion and the λci criterion et al, are Eulerian local region-type vortex identification criteria and can only approximately identify the vortex boundary by somewhat arbitrary threshold. On the other hand, the existing Eulerian local line-type methods, which seek to extract line-type features such as vortex core line, are not entirely satisfactory since most of these methods are based on vorticity or pressure minimum that will fail in many cases. The key issue is the lack of a reasonable mathematical definition for vortex core center. To address this issue, a Liutex (previously named Rortex) based definition of vortex core center is proposed in this paper. The vortex core center, also called vortex rotation axis line here, is defined as a line where the Liutex magnitude gradient vector is aligned with the Liutex vector, which mathematically implies that the cross product of the Liutex magnitude gradient vector and the Liutex vector on the line is equal to zero. Based on this definition, a novel three-step method for extracting vortex rotation axis lines is presented. Two test cases, namely the Burgers vortex and hairpin vortices, are examined to justify the proposed method. The results demonstrate that the proposed method can successfully identify vortex rotation axis lines without any user-specified threshold, so that the proposed method is very straightforward, robust and efficient.

Features of Solving Triple Shear in the Endochronic Theory of Inelasticity Accounting for Large Deformations

The problem of rigid triple shear is solved in the framework of the endochronic theory of inelasticity with account for finite deformations. The numerical implementation of the algorithm for determining the orthogonal rotation tensor and vortex tensor is proposed. The strain tensor is constructed on their basis. Simultaneously, the strain tensor is calculated with a direct numerical method. The corresponding strain components obtained with both methods are compared and analyzed.

Construction and Algorithms of the Onboard System for Measuring the Helicopter Air Data and State of the Atmosphere with a Stationary Receiver, Ion-Mark and Aerometric Measurement Channels

The problem is considered of measuring the air parameters and state of the atmosphere on board the helicopter under the aerodynamic disturbances of the main rotor vortex column. The functional scheme, design features of the air parameter sensor and algorithms of information processing at the parking, starting, takeoff and landing and other modes of helicopter of the onboard system with a fixed receiver, ion-mark and aerometric measurement channels are revealed.