Vortex Circulation Research Articles

Chiral non-Abelian vortices and their confinement in three flavor dense QCD

We find chiral non-Abelian vortices having windings only in one of the diquark condensations of left-handed and right-handed quarks in the color-flavor locked phase of dense QCD. They are the minimum vortices carrying half color magnetic fluxes of those of non-Abelian semi-superfluid vortices (color magnetic flux tubes) and 1/6 quantized superfluid circulations of Abelian superfluid vortices. These vortices carry ${\mathbb C}P^2$ orientational moduli in the internal space corresponding to their fluxes. The ${\mathbb C}P^2$ moduli of two chiral non-Abelian vortices with chiralities opposite to each other are energetically favored to be aligned while those of a vortex and anti-vortex to be orthogonal, and then these vortices attract each other. They are attached by chiral domain walls in the presence of the mass and axial anomaly terms explicitly breaking axial and chiral symmetries. We numerically show that two chiral non-Abelian vortices with chiralities opposite to each other are connected by a chiral domain wall, consisting a mesonic bound state which is nothing but a non-Abelian semi-superfluid vortex. We also show that Abelian and non-Abelian axial vortices attached by chiral domain walls are all unstable to decay into a set of chiral non-Abelian vortices. Furthermore, we find that chiral non-Abelian vortices exhibit unique features: one is the so-called topological obstruction implying that unbroken symmetry generators in the bulk are not defined globally around the vortices, and the other is color non-singlet Aharonov-Bohm (AB) phases implying that quarks encircling these vortices can detect the colors of magnetic fluxes of them at infinite distances.

Characterization of tornado like flows for improving vortex ventilation performance

The innovative local ventilation systems using vortex flows resembling a tornado have been proposed to improve ventilation performance. The effect of two primary operating conditions, the side jet velocity and exhaust flow rate which are essential for the formation of vortex structures and significantly affect the resulting vortex characteristics, on the vortex characteristics are investigated by employing a particle image velocimetry (PIV) technique. The vortex core is widened and the vortex strength increased when the side jet velocity is increased. When the induced swirling force is sufficient, a higher exhaust flow rate can form a stronger and more stable vortex. Vortex characteristics revealed that the optimal side jet velocity is 1.73 m/s corresponding Res of 2332.4 with a normalized exhaust flow rate of 0.155. In order to quantify the effectiveness of the vortex ventilation system, the concentration of ultra-fine particulate matters was monitored. The ventilation performance has a similar trend with vortex size, circulation and swirl ratio over core region. We herein propose a new-type ventilation system and a useful analysis method based on PIV to characterize tornado-like flows in vortex ventilation systems. In addition, these flow and ventilation results can be used as basic data in the design and operation of vortex ventilation systems.

Characteristics of shock tube generated compressible vortex rings at very high shock Mach numbers

Compressible vortex rings are usually formed at the open end of a shock tube. They show exciting flow phenomena during their formation, evolution, and propagation depending on the shock Mach number (Ms) and exit flow conditions. This study considers high shock tube pressure ratio (PR) cases showing hitherto unknown, spectacular flow structures. With hydrogen as a driver section gas at high PR, a supersonic compressible vortex ring having vortex ring Mach number (Mv) >1 is obtained for the first time. The formation of multiple triple points and the corresponding slipstream shear layers and, thus, multiple counter-rotating vortex rings (CRVRs) behind the primary vortex ring at different radial locations, in addition to the usual CRVRs, appears to be a unique characteristic for high Mach number vortex rings. During the formation stage, a vortex layer of reverse circulation than that of the primary vortex ring gets generated from the outer wall of the shock tube. The instability of such a vortex layer creates another series of opposite circulation vortices, which later interfere with the primary vortex core considerably. Also, a near stationary slipstream vortex and multiple fast-moving tiny vortices of opposite circulation to the slipstream vortex are observed near the central zone. Mechanisms for the formation of these complex vortical structures are identified. The implications of these phenomena on the vortex ring's geometric and kinematic characteristics, such as ring diameter, core diameter, circulation, and translational velocity, are discussed in detail, illustrating their differences with low vortex ring Mach number cases considering 0.31 < Mv < 1.08.

Effect of spray properties on aerosol scavenging efficiency with water mist

In the foreseen decommissioning plans of damaged Fukushima Daiichi reactors, submicron aerosol particles will be generated when retrieving fuel debris from reactor buildings by cutting it into small pieces. A multi-nozzle spray system will be used to scavenge these aerosol particles inside the primary containment vessel. To improve the aerosol removal efficiency of the multi-nozzle spray system, it is now necessary to study the aerosol removal performance by different single spray nozzles with different spray properties (spray angle, droplet velocity, etc.). To improve the aerosol scavenging efficiency, a new method with water mist was proposed to aggregate with aerosol particles and form large-sized coagulated aerosol-mist particle clusters, which can subsequently be removed by spray with higher efficiency. In this study, the effect of spray properties on aerosol removal efficiency with preexisting water mist was investigated using three different spray nozzles. The experimental results showed that a larger droplet velocity led to stronger vortex circulation and faster gaseous entrainment from outer spray area into spray region, resulting in a smaller circulation period of gas entrainment by spray and higher aerosol removal efficiency. The numerical simulations of aerosol removal by different spray nozzles without mist were also conducted to provide more insights into the aerosol removal process. By comparing the experiment and simulation results, it is found that the accumulated spray water in the lower plenum of the vessel and the water film formed on the vessel sidewalls also contributed to aerosol removal, especially for the particles with large Stokes numbers.Copyright © 2021 American Association for Aerosol Research

Coupled Aeroelastic Study of a Flexible Micro Air Vehicle-Scale Flapping Wing in Hovering Flight

Instantaneous force and structural deformation experiments were performed on a flexible, structurally characterized, low-aspect-ratio representative flapping wing. A six-component force balance was used to measure aerodynamic-force time history over a flap cycle. A VICON motion capture setup tracked the wing deformations while flapping. Measured aerodynamic forces and wing deformations were compared against coupled computational fluid dynamics/computational structural dynamics (CFD/CSD) aeroelastic analysis results. The CFD solver is an unsteady Reynolds-averaged Navier–Stokes solver. The CSD solver is a general-purpose multibody dynamics solver capable of modeling geometrically nonlinear beam and shell elements. The CFD/CSD results were able to capture the overall trend in aerodynamic forces and wing deformations. Although predicted and measured variations in lift were similar, the drag-force magnitudes tended to be underpredicted by the coupled aeroelastic solver. The coupled CFD/CSD solver was used to evaluate the influence of wing flexibility on wing performance. Results showed that, in particular instances, decreasing wing stiffness increased the time-averaged aerodynamic lift and lift-to-power ratio. Decreased wing stiffness led to reduced leading-edge vortex circulation strength. This suggests that the increased wing performance is mainly due to a redirection of the resultant force vector allowed by the increased wing compliance.

Mitigating Wake Turbulence Risk During Final Approach via Plate Lines

To mitigate the risk of wake vortex encounters during final approach, so-called plate lines have been developed. Wake vortices generated by landing aircraft induce secondary vortices at the plates’ surfaces that approach the primary vortices and trigger premature wake vortex decay. Each plate line consists of several upright plates being installed underneath the approach slope. While the plate line extends perpendicular to the flight direction, its individual plates are oriented in parallel to the runway centerline. To obtain the approval of the authorities for the installation of the plate lines at runway 16 of Vienna International Airport, the plate design had to comply with airport requirements like obstacle clearance, stability, and frangibility. During a six-month campaign, wake vortex behavior of about 9500 landings with and without plates was measured simultaneously by three lidars complemented by a comprehensive suite of meteorological instrumentation. The analysis of over 1000 measured wake vortex evolutions indicates that the plate lines reduce the lifetimes of the vortices in a safety corridor along the final approach by 22–37% depending on the aircraft type. This corresponds to a reduction of vortex circulation by about 50% for the most relevant International Civil Aviation Organization separation (Medium behind Heavy).

A Simple Model for Wildland Fire Vortex–Sink Interactions

A model is developed to explore fire–atmosphere interactions due to the convective sink and vorticity sources in a highly simplified and idealized form, in order to examine their effect on spread and the stability of various fire front geometries. The model is constructed in a cellular automata framework, is linear, and represents a background flow, convective sink, and vortices induced by the fire plume at every burning cell. We use standard techniques to solve the resulting Poisson equations with careful attention to the boundary conditions. A modified Bresenham algorithm is developed to represent convection. The three basic flow types—large-scale background flow, sink flow, and vortex circulation—interact in a complex fashion as the geometry of the fire evolves. Fire-generated vortex–sink interactions produce a range of fire behavior, including unsteady spread rate, lateral spreading, and dynamic fingering. In this simplified framework, pulsation is found associated with evolving fire-line width, a fire-front acceleration in junction fires, and the breakup of longer initial fire lines into multiple head fires. Fuel is very simply represented by a single burn time parameter. The model fuel is uniform yet patchiness occurs due to a dynamic interaction of diffusive and convective effects. The interplay of fire-induced wind and the geometry of the fire front depends also on the fuel burn time.

Volcanic activity sparks the Arctic Oscillation

The parasol effect of volcanic dust and aerosol caused by volcanic eruption results in the deepening and strengthening of the Arctic vortex system, thus stimulating or strengthening the Arctic Oscillation (AO). Three of the strongest AOs in more than a century have been linked to volcanic eruptions. Every significant fluctuation of the AO index (AOI = ΔH_middle latitudes − ΔH_Arctic) for many years has been associated with a volcanic eruption. Volcanic activity occurring at different locations in the Arctic vortex circulation will exert different effects on the polar vortex.

Numerical Analysis of Free Dust Diffusion Law in Large Section Construction Tunnel

The Youzhushan tunnel (large section double-track railway tunnel) is used as the research background, the concentration distribution of the free dust diffusion trajectory after blasting in the working face was numerically simulated by using the finite element computational fluid dynamics software Ansys-CFD. The simulation results were compared with the field measured data, and the results are basically consistent. The results show that the lining trolley is the main equipment to hinder the dust diffusion, the free dust on both sides of the lining trolley has a clear boundary, and the high concentration of free dust has not been well diffused. A vortex area appears near the entrance of the adit level, which forces the free dust from the tunnel to do vortex circulation. The dust removal rate of parallel guide is about 66.5% after 800 seconds of ventilation and about 76.6% after 2400 seconds of ventilation. The drainage effect of parallel guide is more obvious when the dust concentration in the tunnel is lower.

Scaling Analysis on the Dynamic and Instability Characteristics of Isolated Wingtip Vortex

The isolated wingtip vortex is generated by an M6 wing under different angles of attack and Reynolds numbers , and is measured within 16 chord length downstream regions. Then, the spatiotemporal local linear stability analysis (LSA) is performed at the azimuthal wavenumber of to analyze the instability characteristics. Experimental results show that the radial circulation of wingtip vortex satisfies a scaling formula. Moreover, the LSA results demonstrate that the instability characteristics, including the stability curve, growth rate eigenvalue spectrum, and perturbation mode, are uniformed in time and space, laying the basis for scaling the wingtip vortex by considering them. In this situation, by plotting the circulation-based Reynolds number and dimensionless wandering amplitude in log scale, it is found that they are in the form of , where and . Particularly, along with the streamwise development, the swirl number of wingtip vortex asymptotically closes to the unstable region in the (, ) plane defined by Fabre and Jacquin (Journal of Fluid Mechanics, Vol. 500, Jan. 2004, pp. 239–262). By considering the role of growth rate in the vortex wandering, an alternative scaling formula , where and , is suggested to describe the wandering development.

Sensitivity Analysis of Maximum Circulation of Wake Vortex Encountered by En-Route Aircraft

Wake vortex encounters (WVE) can pose significant hazard for en-route aircraft. We studied the sensitivity of wake vortex (WV) circulation and decay to aircraft mass, altitude, velocity, density, time of catastrophic wake demise event, eddy dissipation rate, wing span, span-wise load factor, and WV core radius. Then, a tool was developed to compute circulations of WV generated/encountered by aircraft en-route, while disregarding unrealistic operational conditions. A comprehensive study is presented for most aircraft in the Base of Aircraft Data version 4.1 for different masses, altitudes, speeds, and separation values between generator and follower aircraft. The maximum WV circulation corresponds to A380-861 as generator: 864 and 840 m2/s at horizontal separation of 3 and 5 NM, respectively. In cruise environment, these WV may descend 1000 ft in 2.6 min and 2000 ft in 6.2 min, while retaining 74% and 49% of their initial strength, respectively. The maximum circulation of WV encountered by aircraft at horizontal separation of 3 NM from an A380-861 is 593, 726, and 745 m2/s, at FL200, FL300, and FL395, respectively. At 5 NM, the circulations decrease down to 578, 708, and 726 m2/s. Our results allow reducing WVE simulations only to critical scenarios, and thus perform more efficient test programs for computing aircraft upsets en-route.

Effects of fuel injection speed on supersonic combustion using separation-resistant struts

This paper describes the improvement in combustion efficiency achieved using streamwise vorticity and fuel injections when using hypermixer struts at high Mach numbers. The effects of fuel injection conditions on combustion were investigated using numerical simulations of chemical reactive flows with a detailed reaction mechanism. Hydrogen fuel was injected from the trailing edges of a separation-resistant strut. Fuel injection at sonic speeds led to an enhancement in efficiency with an increased injection angle at Mach number 2.5, but this improvement was not observed at Mach number 3.5. It was found that hydrogen accumulated in the vortex core because of the strong circulation generated from the strut at high Mach numbers. With fuel injection at speeds exceeding the sonic speed, the efficiency increased, and it improved further with an increasing injection angle. From the results, an important indicator for combustion enhancement was derived from the streamwise vortex circulation, fuel injection velocity, and inflow Mach number. To increase the combustion efficiency using the strut, the indicator value should exceed a threshold. This is crucial for ensuring effective fuel consumption during combustion. These findings provide useful insights into a good design of hypermixer struts in supersonic combustion.

An empirical correlation between lift and the properties of leading-edge vortices

Using data from numerical simulations, we show that the lift experienced by both impulsively started and surging airfoils correlates well with the sum of the circulation of the leading-edge vortices truncated at the trailing edge. Therefore, we suggest that reasonable estimates of the lift can be obtained using only two vortex parameters, i.e., its circulation and its position. In addition to being convenient for non-intrusive estimation of forces from PIV measurements, we show that this approach can be used to derive low-order models for the analysis of vortex-lift configurations. In particular, we apply this correlation to model high-amplitude surging, which allows us to quantify the effect of wake-capture mechanisms and to determine the flow parameters that drive optimal lift.

Classification of Flow Modes for Natural Convection in a Square Enclosure with an Eccentric Circular Cylinder

The present study investigated the natural convection for a hot circular cylinder embedded in a cold square enclosure. The numerical simulations are performed to solve a two-dimensional steady natural convection for three Rayleigh numbers of 103, 104 and 105 at a fixed Prandtl number of 0.7. This study considered the wide range of the inner cylinder positions to identify the eccentric effect of the cylinder on flow and thermal structures. The present study classifies the flow structures according to the cylinder position. Finally, the present study provides the map for the flow structures at each Rayleigh number (Ra). The Ra = 103 and 104 form the four modes of the flow structures. These modes are classified by mainly the large circulation and inner vortices. When Ra = 105, one mode that existed at Ra = 103 and 104, disappears in the map of the flow structures. The new three modes appear, resulting in total six modes of flow structures at Ra = 105. New modes at Ra = 105 are characterized by the top side secondary vortices. The corresponding isotherms are presented to explain the bifurcation of the flow structure.

Evaluation of the Effects of Actuator Line Force Smearing on Wind Turbines Near-Wake Development

In the present study, the effects of the actuator line force smearing on the predicted near-wake development of a model wind turbine are evaluated. To exclude the uncertainties related to the blade loads computation, the loads of a corresponding blade-resolving simulation are imposed. Three force projection functions are applied, which all radially scale with the local chord length: an isotropic Gauss force distribution, an anisotropic Gauss distribution with distinct projection widths in the chord and thickness directions, and a Gauss-Gumbel projection function which creates an airfoil-like force distribution in the chord direction. Comparisons with corresponding blade-resolving simulations and experimental results show a good agreement of the tip vortex core size, position and circulation. Comparison of the mid-wake instantaneous streamwise velocity with blade-resolving simulations shows a thinner vortex sheet and stronger effects of the trailed vortices in the actuator line simulation. Although the bound vortex shape scales with the projection function, no significant difference was observed in the resulting tip vortices and near-wake flow field between the three projection functions used. It is attributed to the similar projection width in the tip vortex region for all cases considered. With the chosen grid refinement in the tip vortex area and a smearing width that scales with the chord length, tip vortices that compare with high-resolution experiments and high-fidelity blade-resolving simulation could be generated with the actuator line approach.

Visualization and analysis of coupling between plasmas self-organization and plasma-induced fluid circulation in 1 atm DC glows with liquid anode

In plasma–liquid interactions, the phenomenon of induced liquid flow that originates at the plasma–liquid contact point is important in that it influences mass, charge, and heat transport from the source to the surrounding bulk fluid. Such stimulated flows have been observed in 1 atm glows with a liquid anode. Because the plasma contact point in such discharges is patterned, a natural question is what is the relationship between the observed self-organized patterns and the induced flow field? It is, therefore, of great interest to investigate the coupling mechanism between the self-organization patterns in an atmospheric pressure dc helium glow discharge with a liquid anode and the induced flow circulation. Particle imaging velocimetry is used to probe the flow fields in the plane normal and parallel to the plasma–liquid interface. A strong ascending flow with maximum speed up to 1.5 cm/s and circulation vortices nearby are observed in the plane normal to the interface centered at the plasma attachment. The experiment results suggested that the ascending flow is caused by water evaporation and the vortices are formed by viscous stress. With a self-organization pattern formed, the flow structures become non-static and the circulation vortices are observed to periodically form and decay. In the plane parallel to the interface, a strong swirl flow was found to exist only when the plasma attachment is self-organized. The analysis revealed that the driving mechanism could be the electrohydrodynamics force. Averaged flow velocity over time in the field of view was found to scale linearly with increasing input power and increasing liquid conductivity.

Characteristics and Development Mechanisms of Northeast Cold Vortices

The northeast cold vortices (NECVs) in May-September during 1989–2018 are classified, based on the 6 h NCEP/NCAR reanalysis data (2.5° × 2.5°) and observational data from the Meteorological Information Comprehensive Analysis and Process System (MICAPS) provided by China Meteorological Administration. Meanwhile, characteristics and development mechanisms for NECVs of different types are also analyzed. In the recent 30 years, the occurrences of NECV processes have been increasing year by year, with an average of 7.4 times per year in Northeast China and a duration of 3–5 days on average for each process. NECVs mostly occur in late spring and early summer, and the longest time influenced by NECVs exceeds 19 days, with annual means of 9.9 days, 8.8 days, and 7.0 days in May, June, and July, respectively. The frequency of weak NECVs is about 1.2 times that of strong NECVs. Strong NCVs in late spring and early autumn as well as weak MCVs in summer are with high-frequency occurrences. It is found that when NCVs occur in late spring and early autumn, the upper-level westerly jets are relatively stronger, thus strengthening the divergence in the upper troposphere and the vortex circulation. The circulation fields in upper and lower levels cooperate with the strong jets, promoting the continuous development and maintenance of the cold vortices. Apart from the jets and circulation, the lower central potential height combined with the obvious cold-core and stronger ascending motions favor the NCV’s development. In addition, the dry intrusion has a strong promotion due to the stronger lower-level cold advection and downward intrusion of high potential vorticity. However, when MCVs occur in summer, things are just the opposite.

Efficient degradation of polyacrylate containing wastewater by combined anaerobic–aerobic fluidized bed bioreactors

Polyacrylate containing wastewater (PCW) is the typical sewage discharged by the textile industry. It has extremely poor biodegradability, and chemical methods were used conventionally as the only way for treating PCW. This study is demonstrating a novel biological method. In batch experiment monod kinetics was applied to the experimental data, which indicated that anaerobic treatment used for PCW is feasible. The pilot-scale experiment combined a Spiral Symmetry Stream Anaerobic Bioreactor (SSSAB) and an air-lift external circulation vortex enhancement nitrogen removal fluidized bed bioreactor (AFB). The COD and NH4+-N removal reached up to 95.2% and 96.6%, respectively, which were higher than the value obtained by other chemical methods. High-throughput sequencing analysis indicated that the relative abundance of Proteobacteria, Firmicutes and Bacteroidetes increased, which contribute to the degradation of PCW. Therefore, PCW can be degraded efficiently by using a SSSAB-AFB technique and thus provides an alternative to the chemical methods.

Effect of Airfoil-Preserved Undulation Placement on Wing Performance and Wingtip Vortex

The effect of undulation placement (leading edge, trailing edge, or leading and trailing edges) on the wing performance and the wingtip vortex was investigated. Experiments were performed at the University of Dayton Low-Speed Wind Tunnel on undulated wings where the NACA 0012 airfoil cross section is preserved along the wingspan. Sensitivity studies were done on the undulation wavelength along the span (, 0.21, and 0.15) and undulation placement (leading edge, trailing edge, and both leading and trailing edges). The leading-edge undulations delayed stall until higher angles of attack; however, the maximum aerodynamic efficiency was reduced. The trailing-edge undulated wing, on the other hand, increased the maximum aerodynamic efficiency but was not successful in stall mitigation. Wings with both leading- and trailing-edge undulations showed improvement in aerodynamic efficiency as well as delayed stall. The effect of the undulations on the wingtip vortex was also investigated through Particle Image Velocimetry. For the same coefficient of lift, the undulated wing cases reduced the wingtip vortex circulation by 25%. Investigations into the wingtip vortex core RMS and aerodynamic efficiency revealed a direct relationship where a higher vortex core rms resulted in a higher aerodynamic efficiency, and vice versa.

Experimental investigation of tip anhedral effects on the aerodynamics of a model helicopter rotor in hover

This study experimentally investigates the effects of tip anhedral on the rotor aerodynamic performance and the tip vortex characteristics in hovering flight. A five-bladed scaled helicopter rotor with blades that have either rectangular (baseline) or anhedral tip geometries was used as the experimental model. Thrust and torque measurements were performed at the tip Mach numbers (Mtip) of 0.3 and 0.4 at five different pitch angles. In addition, flow field measurements via phase-locked particle image velocimetry technique were conducted at Mtip = 0.4 for a selected pitch angle. Thrust and torque measurements reveal that the anhedral tip configuration reaches a maximum Figure of Merit (FOM) value of 0.67 yielding approximately 5% FOM improvement when compared to the rectangular blade at Mtip = 0.3. It is observed that the tip anhedral changes the tip vortex trajectory by increasing the radial contraction of the wake and decreasing the average axial convection speed in the range of the wake age considered in this study. The meandering amplitude of the tip vortex increases abruptly after the passage of the proceeding blade in both cases yet a greater increase is observed in the anhedral tip configuration. Moreover, the axial convection of the previously shed tip vortices in the downstream direction is significantly slowed down during the course of the blade passage such that they reside close to the rotor disc in the anhedral case. The resultant proximity of the tip vortices to the blade with anhedral tip configuration promotes the induced flow in the radially inwards direction, which probably attenuates the strength of the newly forming tip vortex. Accordingly, the maximum tangential velocity and circulation of the tip vortex are reduced by 20% and 13%, respectively, when compared to the rectangular blade case. The reduced tip-vortex circulation is consistent with the increased FOM value. A good agreement was found with the Vatistas vortex model using n=3 for the rectangular blade and n=2.2 for the blade with tip anhedral.