Stable Vortex Research Articles

Pattern formations and their active manipulation in a Rydberg noisy-dressed Bose-Einstein condensate.

We investigate the formation and manipulation of spatial patterns and their structural phase transitions by examining the effects of laser linewidth on the dynamics of Rydberg noise-dressed Bose-Einstein condensates (RnD BECs). We discover that the homogeneous matter wave can transition into various types of self-organized patterns, which are manipulated by tuning the laser linewidth, control field intensity, and atomic density. Remarkably, the system exhibits stable nonlocal matter-wave solitons, vortices, and soliton molecules under specific laser linewidths.

Vortex light bullets in rotating Quasi-Phase-Matched photonic crystals

We present a methodology for the generation of stable vortex light bullets (LBs) in rotating Quasi-Phase-Matched (QPM) photonic crystals with quadratic nonlinearity. The photonic crystal is designed with a checkerboard structure, which is feasible to realize by using contemporary technological advancements. Within this framework, square- and rhombus-shaped LBs are observed, both of which are constructed as four-peak vortex mode. The control parameters include the effective phase mismatch, power, rotating frequency, and the size of checkerboard cells. These parameters play key roles in determining the distribution and stability domains of vortex LBs. In contrast to the stable vortex solitons observed in two-dimensional (2D) quadratic systems, the LBs investigated in the 3D rotating system exhibit narrower stability domains within the system’s parameter space. The rotating frequency results in the transition of LBs from quadrupole to traditional vortex modes. Potential applications of this research lie in the field of optical communications and information processing.

Jovian Vortex Hunter: A Citizen Science Project to Study Jupiter’s Vortices

The Jovian atmosphere contains a wide diversity of vortices, which have a large range of sizes, colors, and forms in different dynamical regimes. The formation processes for these vortices are poorly understood, and aside from a few known, long-lived ovals, such as the Great Red Spot and Oval BA, vortex stability and their temporal evolution are currently largely unknown. In this study, we use JunoCam data and a citizen science project on Zooniverse to derive a catalog of vortices, some with repeated observations, from 2018 May to 2021 September, and we analyze their associated properties, such as size, location, and color. We find that different-colored vortices (binned as white, red, brown, and dark) follow vastly different distributions in terms of their sizes and where they are found on the planet. We employ a simplified stability criterion using these vortices as a proxy, to derive a minimum Rossby deformation length for the planet of ∼1800 km. We find that this value of L d is largely constant throughout the atmosphere and does not have an appreciable meridional gradient.

Thermal effect on the flow induced by a single-dielectric-barrier-discharge plasma actuator under steady actuation

The thermal effect of a single-dielectric-barrier-discharge plasma actuator under steady actuation is numerically investigated. A new actuator model is proposed and validated using experimental data. A discrete Galerkin method based on high-order flux reconstruction schemes is employed to solve the flow governing equations and the actuator model equations on unstructured quadrilateral grids. By comparing the induced heated and cold flow fields of the actuator with and without a plasma thermal source, its thermal effect is revealed. The actuator generates a thermal wall jet with rich vorticity, forming a monopolar starting vortex with a high-temperature and low-density core. Over time, the starting vortex becomes unstable and transforms into a dipole. Actuator heating enhances jet velocity and width, as well as vortex stability, while slowing down vorticity generation. The relative change in density and temperature fields due to actuator heating is four orders of magnitude greater than that without actuator heating. Additionally, the actuator heating causes the background thermodynamic fields to increase approximately linearly with time. Two stages in the actuator's thermal effect are distinguished due to time accumulation. Initially, the actuator heating minimally affects the monopolar starting vortex motion, and the temperature and density fields are treated as passive variables driven by the velocity field. During this stage, the momentum and thermal effects of the actuator can be studied separately. However, after the starting vortex becomes unstable, the actuator heating significantly impacts its motion and morphology, and these two effects are coupled with each other.

Efficient approach for generating vortex sources with arbitrary orbital angular momentum in acoustic experiments

Abstract In theoretical research framework of acoustics or optics, how to provide stable and efficient experimental vortex sources with arbitrary orbital angular momentum (OAM) (especially with larger OAM) is a highly challenging research topic. Here, we propose and demonstrate the general principle of two different methods to generate vortex sources with arbitrary OAM, based on the point-sources array and acoustic metamaterials, respectively. Specifically, the general synthetic law is summarized from the analytical perspective behind generating two-dimensional vortex waves using different point sources with different phases, and the design flexibility of acoustic metamaterials is also utilized to provide an ideal solution for generating vortex sources with larger OAM. Besides, we qualitatively and quantitatively determine the OAM of generated vortex waves through simple formulas, and briefly discuss the applicability and stability of two different methods with complementary advantages. The principles of vortex sources generation revealed in this work provide direct theoretical support for the experimental exploration of interactions between multiphysics fields and complex media, with potential applications in vortex fields manipulation and OAM detection.

Effects of inlet air holes on swirl flow characteristics and outlet temperature distribution in an axial swirl combustor

The air inlet holes on the swirl combustor are crucial for high-performance micro gas turbine (MGT), affecting internal airflow, fuel-air mixing, temperature distribution, and cooling. However, there are seldom studies that pay attention to the influence of the air inlet holes coupled with low volatility macromolecular fuels for fast and better fuel-air mixing and combustion processes in MGT. This study investigates the influence of primary and dilution hole positions on airflow, temperature, emissions, and combustion efficiency. Numerical simulations in ANSYS Fluent examine five inlet hole configurations in a two-stage axial swirl combustor. Simulation validation is conducted under three test conditions. The results showed that the cut-off effect of the primary hole affected the size of the swirl vortex core, and the backward movement of the primary hole resulted in a significant increase in the length of the recirculation zone and the coherence high-temperature zone, accelerated the droplet evaporation rate, and reduced CO and NO emissions. Backward movement of dilution hole alters flow field, affecting swirl vortex stability and reflow intensity. Case 3, with original dilution hole and backward extended primary hole, exhibits optimal outlet temperature distribution and combustion efficiency.

Asymptotic estimates for concentrated vortex pairs

Burton-Lopes Filho-Nussenzveig Lopes (2013) [6] studied the existence and stability of slowly traveling vortex pairs as maximizers of the kinetic energy penalized by the impulse relative to a prescribed rearrangement class. In this paper, we prove that after a suitable scaling transformation the maximization problem studied by Burton-Lopes Filho-Nussenzveig Lopes in fact gives rise to a family of stable concentrated vortex pairs approaching a pair of point vortices with equal magnitude and opposite signs. The key ingredient of the proof is to deduce a uniform bound for the size of the supports of the scaled maximizers.

Analysis of Vortex Stability During the BOF Tapping Process

Analysis of Vortex Stability During the BOF Tapping Process

Quantum vortex stability in draining fluid flows

Quantum vortices with more than a single circulation quantum are usually unstable and decay into clusters of smaller vortices. One way to prevent the decay is to place the vortex at the center of a convergent (draining) fluid flow, which tends to force vortices together. It is found that while the primary splitting instability is suppressed in this way (and completely quenched for strong enough flows) a secondary instability can emerge in circular trapping geometries. This behavior is related to an instability of rotating black holes when superradiantly amplified waves are confined inside a reflective cavity. The end state of the secondary instability is dramatic, manifesting as a shock wave that propagates round the circular wall and nucleates many more vortices. Published by the American Physical Society 2024

Optical vortex-antivortex crystallization in free space

Stable vortex lattices are basic dynamical patterns which have been demonstrated in physical systems including superconductor physics, Bose-Einstein condensates, hydrodynamics and optics. Vortex-antivortex (VAV) ensembles can be produced, self-organizing into the respective polar lattices. However, these structures are in general highly unstable due to the strong VAV attraction. Here, we demonstrate that multiple optical VAV clusters nested in the propagating coherent field can crystallize into patterns which preserve their lattice structures over distance up to several Rayleigh lengths. To explain this phenomenon, we present a model for effective interactions between the vortices and antivortices at different lattice sites. The observed VAV crystallization is a consequence of the globally balanced VAV couplings. As the crystallization does not require the presence of nonlinearities and appears in free space, it may find applications to high-capacity optical communications and multiparticle manipulations. Our findings suggest possibilities for constructing VAV complexes through the orbit-orbit couplings, which differs from the extensively studied spin-orbit couplings.

Vortex rope identification in Francis turbine based on cyclostationary extended dictionary learning

Francis turbine is one of the most commonly used hydraulic machinery for hydroelectric power generation, but its stability is frequently jeopardized by vortex rope. It is crucial to promptly and accurately detect vortex rope for the reliable operation of turbine unit. To address this challenge, the Cyclostationary Extended Dictionary Learning (CEDL) approach is proposed to identify vortex rope in Francis turbine. CEDL utilizes the Fisher discrimination criterion and low-rank constraints through the preprocessing and extending strategies to achieve accurate identification. Preprocessing specifically refers to the construction of filter for raw data based on cyclostationarity Then, the trained dictionary is used to extract features, and a linear classifier is developed based on these features. To evaluate the proposed method, vortex rope experiments are conducted in a Francis turbine under five conditions, and every condition includes four states: normal state, initial vortex rope, stable vortex rope and severe vortex rope. The results reveal three main findings. Firstly, the trained atoms in each sub-dictionary exhibit unique characteristics such as tonal frequency at 7 kHz and broadband frequency during 12–20 kHz, which are linked to the evolution stages of vortex rope. Secondly, the dictionary trained for a specific condition can achieve a classification accuracy of up to 90%, and even exceed 97% in some cases. Finally, the dictionary trained in a specific working condition can achieve relatively high classification accuracy in the scenarios of other working conditions.

Influence of magnetic anisotropy on the vortex stability in circular Permalloy nanodots using energy analysis

We thoroughly investigated the stability of vortex magnetization in Permalloy (Py) circular nanodots with and without magnetocrystalline anisotropy using micromagnetic simulations. This study explores a wide-ranging understanding of influence of anisotropy on hysteresis loops, and spin-configurations, and provides a detailed analysis of the energy profile. The ground state vortex configuration considered of size 64 × 20-nm2 Py-nanodot at zero out-of-plane anisotropy had been modulated till the anisotropy 250 kJ/m3. We analyzed different energy terms at nucleation field, annihilation field and remanent states to gain deeper insights into the magnetization reversal mechanism. The energy analysis revealed an interplay between exchange and demagnetization energies, resulting in the stability of vortex up to a critical anisotropy (CK) 170 kJ/m3. Beyond this CK, the vortex destabilizes, switching the magnetization to a single-domain state. Additionally, we estimated the energy barrier involved in single domain to vortex state transformation. These findings provide valuable insights for designing vortex-based magnetic data storage and memory devices.

The synthetic gauge field and exotic vortex phase with spin-orbital-angular-momentum coupling

Ultracold atoms endowed with tunable spin-orbital-angular-momentum coupling (SOAMC) represent a promising avenue for delving into exotic quantum phenomena. Building on recent experimental advancements, we propose the generation of synthetic gauge fields, and by including exotic vortex phases within spinor Bose–Einstein condensates, employing a combination of a running wave and Laguerre–Gaussian laser fields. We investigate the ground-state characteristics of the SOAMC condensate, revealing the emergence of exotic vortex states with controllable orbital angular momenta. It is shown that the interplay of the SOAMC and conventional spin-linear-momentum coupling induced by the running wave beam leads to the formation of a vortex state exhibiting a phase stripe hosting single multiply quantized singularity. The phase of the ground state will undergo the phase transition corresponding to the breaking of rotational symmetry while preserving the mirror symmetry. Importantly, the observed density distribution of the ground-state wavefunction, exhibiting broken rotational symmetry, can be well characterized by the synthetic magnetic field generated through light interaction with the dressed spin state. Our findings pave the way for further exploration into the rotational properties of stable exotic vortices with higher orbital angular momenta against splitting in the presence of synthetic gauge fields in ultracold quantum gases.

Generating Optical Vortex Array Laser Beams of Superimposing Hermite–Gaussian Beams with a Dual–Phase Modulation Digital Laser System

This study presents an efficient and practical intra-cavity approach for selectively generating vortex array laser beams employing a dual-phase modulation digital laser system, which has not yet been completed in single-phase modulation digital laser. The stable optical vortex array laser beams were formed by superimposing cavity Hermite–Gaussian (HG) eigenmodes. In particular, when the selected cavity HG modes shared the same Gouy phase, the resulting optical vortex beam could preserve its light field pattern, thereby maintaining the optical vortex properties in the near and far fields. Numerical results demonstrated that employing dual-phase modulation could establish optimal boundary conditions for the selection of HG modes within the cavity, successfully generating various vortex array laser beams. The experimental validation of the proposed method confirmed the ability to select optical vortex array lasers solely by controlling the loaded phase of the dual-phase modulation digital laser. These results demonstrate the ability of digital lasers to generate and dynamically control optical vortex array lasers.

Investigating the unsteady flow mechanism at the lip of a ducted fan in crosswind

The unsteady numerical analysis method was utilized to investigate the unsteady flow structure of a contra-rotating ducted fan under crosswind conditions. The development and evolution mechanism of the lip vortex under the combined action of crosswind and rotor were studied. Two perspectives, namely the time-averaged flow field and unsteady time-frequency analysis, were employed for the examination. The results indicate that the unsteady aerodynamic forces exerted on the lip of the ducted fan are primarily influenced by four sets of frequencies, ranked in descending order of magnitude: 1 BPF (Blade Passing Frequency) of the upstream rotor, 1 BPF of the downstream rotor, the combined effect of the 1 BPF of the upstream rotor and 1 BPF of the downstream rotor, and 2 BPF of the upstream rotor. The maximum velocity occurs at the position where the inner surface of the windward side lip is inclined 40° from the freestream velocity direction, and a stable separation vortex is formed below this region. The lip separation vortex triggers the generation of blade suction side separation vortex in the upstream rotor, and its periodic formation, growth, shedding, and dissipation are the primary factors contributing to the unsteady flow. The research findings lay the groundwork for further advancements in active and passive flow control technologies under crosswind conditions.

Semivortex solitons and their excited states in spin-orbit-coupled binary bosonic condensates.

It is known that two-dimensional two-component fundamental solitons of the semivortex (SV) type, with vorticities (s_{+},s_{-})=(0,1) in their components, are stable ground states (GSs) in the spin-orbit-coupled (SOC) binary Bose-Einstein condensate with the contact self-attraction acting in both components, in spite of the possibility of the critical collapse in the system. However, excited states (ESs) of the SV solitons, with the vorticity set (s_{+},s_{-})=(S_{+},S_{+}+1) and S_{+}=1,2,3,..., are unstable in the same system. We construct ESs of SV solitons in the SOC system with opposite signs of the self-interaction in the two components. The main finding is stability of the ES-SV solitons, with the extra vorticity (at least) up to S_{+}=6. The threshold value of the norm for the onset of the critical collapse, N_{thr}, in these excited states is higher than the commonly known critical value, N_{c}≈5.85, associated with the single-component Townes solitons, N_{thr} increasing with the growth of S_{+}. A velocity interval for stable motion of the GS-SV solitons is found too. The results suggest a solution for the challenging problem of the creation of stable vortex solitons with high topological charges.

Impact of the Polar Vortex on Sub‐Seasonal O/N2 Variability in the Lower Thermosphere Using GOLD and WACCM‐X

AbstractWe provide observational evidence that the stability of the stratospheric Polar vortex (PV) is a significant driver of sub‐seasonal variability in the thermosphere during geomagnetically quiet times when the PV is anomalously strong or weak. We find strong positive correlations between the Northern Annular Mode (NAM) index and subseasonal (10–90 days) Global Observations of the Limb and Disk (GOLD) O/N2 perturbations at low to mid‐northern latitudes, with a largest value of +0.55 at ∼30.0°N when anomalously strong or weak (NAM >2.5 or < −2.1) vortex times are considered. Strong agreement for O/N2 variability and O/N2‐NAM correlations is found between GOLD observations and the Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCM‐X) simulations, which is then used to delineate the global distribution of O/N2‐NAM correlations. We find negative correlations between subseasonal variability in WACCM‐X O/N2 and NAM at high northern and southern latitudes (as large as −0.54 at ∼60.0°S during anomalous vortex times). These correlations suggest that PV driven upwelling at low latitudes is accompanied by corresponding downwelling at high latitudes in the lower thermosphere (∼80–120 km), which is confirmed using calculations of residual mean meridional circulation from WACCM‐X.

Biomimetic swallowtail V-shaped attachments for enhanced low-speed wind energy harvesting by a galloping piezoelectric energy harvester

Efficient low wind speed energy harvesting is pivotal in expanding the reach of sustainable wind power to regions with limited wind resources. This paper introduces an innovative approach to enhance wind energy harvesting efficiency in low wind speed environments through the development of a biomimetically inspired design featuring V-shaped attachments on a square bluff body. Drawing inspiration from the swallowtail, these attachments are engineered to manipulate airflow, creating an asymmetrical pressure field that significantly improves the vibration amplitude of the harvesting device. The proposed design is tested in wind tunnel experiments, demonstrating a 32 % reduction in cut-in wind speed and a significant increase in power output at the lowest tested wind speed of 1.7 m/s, compared to traditional designs. Computational fluid dynamics simulations further elucidate the mechanism behind the enhanced energy harvesting, highlighting the role of V-shaped attachments in generating stronger and more stable vortex shedding, crucial for efficient energy harvesting. The proposed attachments not only substantially reduce the cut-in wind speed of galloping but also significantly increase the device's power output, demonstrating the potential of this design for expanding the viability of wind energy in regions with limited wind resources.

Investigation of stabilization and survival of skyrmion vortices in the presence of magnetic field disorder in two-dimensional lattices: a case study for Janus dichalcogenides

Due to the lack of inversion symmetry, very large Dzyaloshinskii–Moriya interaction (DMI) has been reported for a series of Janus monolayers of manganese dichalcogenides within the framework of first-principles calculations (Liang et al 2020 Phys. Rev. B 101 184401). However, from the viewpoint of potential applications, the current ongoing research mainly focuses on the magnetism in pristine two-dimensional (2D) materials exhibiting non-zero DMI, and the effects of disorder in such systems remain an open problem since the influence of randomness may create some drastic effects on the magnetism of low dimensional systems. Here, we present Monte Carlo simulation results regarding the magnetic properties of a 2D manganese based Janus dichalcogenide material MnSTe in the presence of quenched random magnetic fields where the local field variables have been sampled from a Gaussian distribution. For the selected benchmark material, it has been found that the magnetic skyrmion vortexes emerging at (10 K, 3 T) may survive in the presence of weak and moderate quenched randomness, which is important from the viewpoint of technological applications. In both the pristine and random field cases, the stabilization of magnetic skyrmions are achieved by the major contribution of the ferromagnetic exchange energy to the total energy of the system, and the materials exhibiting large DMI/exchange ratios may exhibit resilient magnetic skyrmion vortexes in the presence of weak and moderate amount of randomness.

Multi-jet impingement cooling in the leading edge of turbine blade using matrix as internal structure

Multi-jet impingement is a competitive cooling scheme for the turbine blade leading edge, due to its strong ability in suppressing thermal boundary layer and quickly releasing the thermal load. However, crossflow is always a challenge if thermal performance is expected to be further improved. This paper proposed to induce jet flow from matrix to enhance cooling capability as well as uniformity of leading edge. A dual-air-paths test rig is built to measure heat transfer distribution and to validate the computational method. The results indicated strong coupling between jet cavity and matrix, implying the potential of enhancing heat transfer on both ends. Comparisons are made between different jet hole locations, among which the “Stagnation” position yields best performance, since superior initial jet condition can be created by matrix sub-channel flow. Increasing jet hole aperture leads to elevated heat transfer of nearly 72% in jet cavity, due to more stable vortex scour on the target wall. Changing jet cavity outflow configuration has significant effect on heat transfer due to thorough reconstruction of thermal field. The most advanced performance is acquired by both-sides outflow configuration, with approximately 34% improvement in heat transfer compared to the single-side cases.