Search Results (396)

The interaction between a shock wave and a boundary layer promotes corner separation and prevents performance enhancement in a supersonic compressor cascade. Different vortex generator (VG) designs are presented to control corner separation in a supersonic compressor cascade, including endwall VGs (EVG), suction surface VGs (SVG), and combined endwall and suction surface VGs (E-SVGs). It is demonstrated that EVG and coupled E-SVGs reduce losses in the supersonic compressor cascade. For an optimal EVG, the total loss is reduced by 24.6% and the endwall loss is reduced by 33.6%. The coupled E-SVG better controls corner separation and reduces endwall losses by 56.9%. The suppression mechanism is that vortices alter the direction of the separated flow, allowing it to overcome the chordwise pressure gradient. Moreover, the VGs change the shock structure near the endwall. For the EVG, clockwise vortices are effective in controlling corner separation due to their minor effect on the shock structure near the endwall. However, anticlockwise vortices are not suitable for controlling corner separation in the supersonic compressor because they increase the shock strength induced by the VG. The control mechanism of the coupled E-SVG on corner separation is also discussed. Full article

The current study examines the influence of a varying gravity field and its interaction with density stratification. This represents a novel area in baroclinic flow analysis. The classical vortex and internal wave structures in stratified flows are shown to be significantly modified when gravity varies with height. Vortices may shift, stretch, or weaken depending on the direction and strength of gravity variation, and internal waves develop asymmetries or damping that are not present under constant gravity. We examine the influence of gravity variation on the flow of both homogeneous and density-stratified fluids in a channel with topography consisting of a Gaussian obstacle lying at the bottom of the channel. The flow is without inertia, induced by the translation of the top plate. Both the density and gravity are assumed to vary linearly with height, with the minimum density at the moving top plate. The narrow-gap approach is used to generate the flow field in terms of the pressure gradient along the top plate, which, in turn, is obtained in terms of the bottom topography and the three parameters of the problem, namely, the Froude number and the density and gravity gradients. The resulting stream function is a fifth-order polynomial in the vertical coordinate. In the absence of stratification, the flow is smooth, affected rather slightly by the variable topography, with an essentially linear drop in the pressure induced by the contraction. For a weak stratified fluid, the streamlines become distorted in the form of standing gravity waves. For a stronger stratification, separation occurs, and a pair of vortices generally appears on the two sides of the obstacle, the size of which depends strongly on the flow parameters. The influence of gravity stratification is closely coupled to that of density. We examine conditions where the coupling impacts the pressure and the velocity fields, particularly the onset of gravity waves and vortex flow. Only a mild density gradient is needed for flow separation to occur. The influence of the amplitude and width of the obstacle is also investigated. Full article

Energy generation from renewable sources has increased exponentially worldwide, particularly wind energy, which is converted into electricity through wind turbines. The growing demand for renewable energy has driven the development of horizontal-axis wind turbines with larger dimensions, as the energy captured is proportional to the area swept by the rotor blades. In this context, the dynamic loads typically observed in wind turbine towers include vibrations caused by rotating blades at the top of the tower, wind pressure, and earthquakes (less common). In offshore wind farms, wind turbine towers are also subjected to dynamic loads from waves and ocean currents. Vortex-induced vibration can be an undesirable phenomenon, as it may lead to significant adverse effects on wind turbine structures. This study presents a two-dimensional transient model for a rigid body anchored by a torsional spring subjected to a constant velocity flow. We applied a coupling of the Fourier pseudospectral method (FPM) and immersed boundary method (IBM), referred to in this study as IMERSPEC, for a two-dimensional, incompressible, and isothermal flow with constant properties—the FPM to solve the Navier–Stokes equations, and IBM to represent the geometries. Computational simulations, solved at an aspect ratio of $\varphi =4.0$, were analyzed, considering Reynolds numbers ranging from $Re=150$ to Re = 1000 when the cylinder is stationary, and $Re=250$ when the cylinder is in motion. In addition to evaluating vortex shedding and Strouhal number, the study focuses on the characterization of space–time symmetry during the galloping response. The results show a spatial symmetry breaking in the flow patterns, while the oscillatory motion of the rigid body preserves temporal symmetry. The numerical accuracy suggested that the IMERSPEC methodology can effectively solve complex problems. Moreover, the proposed IMERSPEC approach demonstrates notable advantages over conventional techniques, particularly in terms of spectral accuracy, low numerical diffusion, and ease of implementation for moving boundaries. These features make the model especially efficient and suitable for capturing intricate fluid–structure interactions, offering a promising tool for analyzing wind turbine dynamics and other similar systems. Full article

From the point of view of the intelligent operation and maintenance of high-speed train tracks, this paper examines the research status of high-speed train rail damage detection technology in the field of high-speed train track operation and maintenance detection in recent years, summarizes the damage detection methods for high-speed trains, and compares and analyzes different detection technologies and application research results. The analysis results show that the detection methods for high-speed train rail damage mainly focus on the research and application of non-destructive testing technology and methods, as well as testing platform equipment. Detection platforms and equipment include a new type of vortex meter, integrated track recording vehicles, laser rangefinders, thermal sensors, laser vision systems, LiDAR, new ultrasonic detectors, rail detection vehicles, rail detection robots, laser on-board rail detection systems, track recorders, self-moving trolleys, etc. The main research and application methods include electromagnetic detection, optical detection, ultrasonic guided wave detection, acoustic emission detection, ray detection, vortex detection, and vibration detection. In recent years, the most widely studied and applied methods have been rail detection based on LiDAR detection, ultrasonic detection, eddy current detection, and optical detection. The most important optical detection method is machine vision detection. Ultrasonic detection can detect internal damage of the rail. LiDAR detection can detect dirt around the rail and the surface, but the cost of this kind of equipment is very high. And the application cost is also very high. In the future, for high-speed railway rail damage detection, the damage standards must be followed first. In terms of rail geometric parameters, the domestic standard (TB 10754-2018) requires a gauge deviation of ±1 mm, a track direction deviation of 0.3 mm/10 m, and a height deviation of 0.5 mm/10 m, and some indicators are stricter than European standard EN-13848. In terms of damage detection, domestic flaw detection vehicles have achieved millimeter-level accuracy in crack detection in rail heads, rail waists, and other parts, with a damage detection rate of over 85%. The accuracy of identifying track components by the drone detection system is 93.6%, and the identification rate of potential safety hazards is 81.8%. There is a certain gap with international standards, and standards such as EN 13848 have stricter requirements for testing cycles and data storage, especially in quantifying damage detection requirements, real-time damage data, and safety, which will be the key research and development contents and directions in the future. Full article

As the core components of geophysical dynamic system, oceans and atmospheres are dominated by the Coriolis force, which governs complex dynamic phenomena such as internal waves, gravity currents, vortices, and others involving multi-scale spatiotemporal coupling. Due to the limitations of in situ observations, large-scale rotating tanks have emerged as critical experimental platforms for simulating Earth’s rotational effects. This review summarizes recent advancements in rotating tank applications for studying oceanic flow phenomena, including mesoscale eddies, internal waves, Ekman flows, Rossby waves, gravity currents, and bottom boundary layer dynamics. Advanced measurement techniques, such as particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF), have enabled quantitative analyses of internal wave breaking-induced mixing and refined investigations of vortex merging dynamics. The findings demonstrate that large-scale rotating tanks provide a controllable experimental framework for unraveling the physical essence of geophysical fluid motions. Such laboratory experimental endeavors in a rotating tank can be applied to more extensive scientific topics, in which the rotation and stratification play important roles, offering crucial support for climate model parameterization and coupled ocean–land–atmosphere mechanisms. Full article

In this study, an unsteady vortex element method is applied to the analysis of a horizontal wing in order to investigate its propulsive performance when operating as a biomimetic thruster. The foil undergoes a combined heaving and pitching motion at the same frequency, in a uniform inflow condition, due to its advance at a constant speed. The numerical results are presented and compared to experimental measurements for the propulsion thrust coefficient and the efficiency of the system over a range of motion parameters. The results indicate the significance of 3D effects and show that the present technique can serve for the design of this kind of propulsive system with optimized performance. In the next stage, the wing is examined in a horizontal T-foil arrangement at the bow of a ship as an efficient propulsion system, and its performance in irregular head waves, characterized by a frequency spectrum, is also studied using experiments in a towing tank. In the test cases, a 30% damping of the ship responses in waves is observed with a simultaneous decrease in the total resistance by 5%. The numerical results are compared with data obtained from tank experiments, revealing good agreement, demonstrating the applicability of the present method to the preliminary design of this system for the augmentation of ship propulsion in waves. Full article

Rip currents at featureless beaches (i.e., beaches lacking sandbars or channels) are often hydrodynamically controlled, exhibiting intermittent and unpredictable behaviors that pose significant risks to recreational beach users. This study assessed occurrences of rip currents under a range of idealized morphology configurations and hydrodynamic wave forcing parameters using a wave-resolving Boussinesq-type model. Numerical experiments revealed that rip currents with durations on the time scale of 10 min are generated in the forms of vortex pairs, intensified eddies, mega-rips, and eddies shedding from longshore currents. In general, the key conditions that promote rip current formation at featureless beaches include shoreline curvature, headlands, moderately mild beach slopes (e.g., 0.02–0.03), normal or near-normal wave incidence, and large wave heights. Most importantly, this study highlights inherent uncertainties in rip current occurrences, particularly under conditions usually perceived as low risk: low wave heights, short wave periods, oblique wave incidence, and straight shorelines. These conditions can lead to transient rip currents and pose an unexpected hazard that coastal communities should be aware of. Full article

This study investigates the organized flow structures and turbulence quantities in a transitional oscillatory boundary-layer flow over a smooth bed using a DNS model set up by the open-source framework Nektar++ (v5.2.0). The present model was validated against the results of a previous study involving a bypass transition mechanism in the intermittently turbulent regime. To trigger the initial perturbations, a roughness element was placed on the bed and removed at the very moment a two-dimensional vortex tube, caused by an inflectional-point shear-layer instability, was observed on it. Then, the turbulent spots where the flow experienced intense fluctuations in an otherwise laminar boundary layer were identified from the bed shear-stress distribution on the bed, which served as a reliable indicator of turbulence. These flow features emerged as the first sign of the initiation of turbulence. Several measurement points were selected to follow the bed shear-stress variations and to observe the spatial and temporal development of turbulent spots at a low-wave Reynolds number, $Re=1.8\times {10}^5$. Along with these observations, phase-resolved turbulence quantities were also investigated over successive half-cycles for the first time in the literature to understand how turbulence develops and spreads over the flow domain. The results show that the turbulence generated in the near-bed region becomes stronger in the deceleration stage due to the adverse pressure gradient and diffuses away from the bed during the subsequent phases of the developing oscillatory boundary-layer flow. The findings related to the turbulence quantities also indicate that the turbulence gradually evolves and spreads into the fluid domain in successive half-cycles. Full article

With the increasing global population and migration toward coastal regions, and the rising demand for coastal urbanization, including the development of living spaces, ports, and tourism infrastructure, the need for coastal defense structures (CDSs) is also increasing. Traditional CDSs, such as breakwaters, typically composed of hard units designed to block and divert wave and current energy, often fail to support diverse and abundant marine communities because of their impact on current and sediment transport, the introduction of invasive species, and the loss of natural habitats. Marine ecoengineering aims at increasing CDS ecological services and the development of marine organisms on them. In this study, carried out in a coral reef environment, we examined the relationship between coral colony protection levels and three factors related to their development, namely, coral fragment survival rate, larval settlement, and water motion (flow rate), across three distinct niches: Exposed, Semi-sheltered, and Sheltered. Coral survivability was assessed through fragment planting, while recruitment was monitored using ceramic settlement tiles. Water motion was measured in all defined niches using plaster of Paris Clod-Cards. Additionally, concrete barrier structures were placed in Exposed niches to test whether artificially added protective elements could enhance coral fragment survival. No differences were found in coral settlement between the niches. Flow rate patterns remained similar in Exposed and Sheltered niches due to vortex formation in the Sheltered zones. Survival analysis revealed variability between niches, with the addition of artificial shelter barriers leading to the highest coral fragment survival on the breakwater. This study contributes to the development of ways to enhance coral development with the goal of transforming artificial barriers into functional artificial reefs. Full article

This paper investigates the significance of various physical factors affecting the wave generated by submerged jet and the synchronization relationship between the wave surface process and different fluid dynamic parameters, based on three-dimensional numerical simulations using a large eddy simulation (LES) model. An orthogonal experimental design was employed, and range analysis and variance analysis revealed that the orifice contraction ratio has the most significant effect on wave height, followed by upstream water depth and orifice elevation. Through wavelet coherence and spectral correlation analysis, the wave surface process was examined in relation to fluid kinetic energy, Reynolds stress, and vortex structure parameters along the jet axis. The results indicate that regions of strong wavelet coherence are concentrated between 0.01 and 1.0 Hz. In the low-frequency range (0.01~1.0 Hz), there are narrow yet continuous coherence bands, while in the slightly higher frequency range (1.0~5.0 Hz), intermittent coherence relationships with wider bands are observed. Additionally, there is a certain degree of correlation between the power spectral density of the wave surface process and these physical quantities, with a maximum spectral correlation coefficient reaching 0.91. This study contributes to a deeper understanding of the factors affecting waves generated by submerged jets, enabling better prediction and control of their effects. Full article

Arterial diseases are a leading cause of morbidity worldwide, necessitating the development of robust simulation tools to understand their progression mechanisms. In this study, we present a finite volume solver based on the incompressible lattice Boltzmann method (iLBM) to model complex cardiovascular flows. Standard LBM suffers from compressibility errors and is constrained to uniform Cartesian meshes, limiting its applicability to realistic vascular geometries. To address these issues, we developed an incompressible LBM scheme that recovers the incompressible Navier–Stokes equations (NSEs) and integrated it into a finite volume (FV) framework to handle unstructured meshes while retaining the simplicity of the LBM algorithm. The FV-iLBM model with linear reconstruction (LR) scheme was then validated against benchmark cases, including Taylor–Green vortex flow, shear wave attenuation, Womersley flow, and lid-driven cavity flow, demonstrating improved accuracy in reducing compressibility errors. In simulating flow over National Advisory Committee for Aeronautics (NACA) 0012 airfoil, the FV-iLBM model accurately captured vortex shedding and aerodynamic forces. After validating the FV-iLBM solver for simulating non-Newtonian flows, pulsatile blood flow through an artery afflicted with multiple stenoses was simulated, accurately predicting wall shear stress and flow separation. The results establish FV-iLBM as an efficient and accurate method for modeling cardiovascular flows. Full article

Vortex beams characterized by helical phase wavefronts enable innovative explorations of optical and physical interactions. This work experimentally realizes longitudinally polarized vortices with arbitrary topological charges in terahertz (THz) frequencies using a silicon ring resonator integrated with a second-order diffraction grating. The implemented configuration enables flexible topological charge manipulation in longitudinally polarized electric fields through the excitation of quasi-transverse-magnetic (TM) waveguide modes with different frequencies. By employing a terahertz near-field measurement system, the spatial intensity patterns and phase characteristics of emitted waves are quantitatively analyzed via a precision probe. This strategy shows promising potential for applications in particle manipulation techniques and advanced imaging technologies. Full article

Field observations revealed that a mooring buoy rapidly drifts in a reciprocating motion along an arcuate path between two extreme positions. When the anchor point is considered the origin and viewed from an aerial perspective, this movement resembles a pendulum. The implications of this motion for data acquisition efficiency prompted our inquiry into this phenomenon. The comparative analysis of the model’s different movements under wave-only, current-only, and wave–current conditions demonstrates that currents are the source inducing this pendulum-like motion. To investigate the mechanism of this current-driven motion, the flow field around the buoy was visualized through numerical simulations. Specifically, the CFD results aligned with the field data and confirmed that periodic vortex shedding induces oscillatory forces, which dominate the rapid reciprocating movement. The findings emphasize the significant impact of fluid viscosity and the resulting vortex effects on the motion characteristics of buoys. They can provide a foundation for addressing more applied problems of data error-correcting and trajectory predictions. Full article

In this paper, the far-field topological structures (FFTSs) of the second harmonic (SH) from higher-order Poincaré sphere (HOPS) beams, including circularly polarized vortex beams (VBs), cylindrically vector beams (CVBs) and elliptically polarized CVBs (EPCVBs), were demonstrated and reported. To begin with, the hidden FFTSs of the SH after propagating the twice Rayleigh range were simulated based on the vectorial coupled wave equations and the Collins formula. Then, the experimental setup was established to achieve the SH from the HOPS by applying two orthogonal 5% MgO: PPLN crystals, the FFTSs of which were demonstrated. The theoretical and experimental results indicate that for the circularly polarized VBs, the FFTSs of the SH still exhibit the 135°-linearly polarized VBs, which is similar to that of the SH in-source plane, because the SH is the eigen-mode of free space, while for the CVBs, the FFTSs of the SH generally show the disappearance of the central dark core, replaced by the maximum light intensity at the center due to the topological phase transition during propagation. Especially of note, for the EPCVBs, the FFTSs of the SH display the maximum light intensity at the center, but the FFTSs in the horizontal and vertical directions reveal rotational symmetry related to the chirality of the EPCVBs. The results reveal the evolution mechanisms of the SH from the HOPS in the far field, which may facilitate the applications of the SH from HOPS beam. Full article

Free spans of submarine pipelines are prone to be subjected to vortex-induced vibration (VIV) under the action of currents, leading to fatigue damage of submarine pipelines. In the traditional method, the fatigue damage is predicted assuming that the length of free span is a constant. However, the free-span length may vary in time and space due to local scour and sand wave migration in engineering practice. This study proposed probabilistic methods to predict the fatigue life of the free spans by considering the effect of variant span length and span position. Truncated Gaussian, Raileigh and Uniform distributions of span length due to local scour, and a sinusoidal pattern with a constant migration rate is assumed for the sand wave due to the lack of field scan data. The fatigue life of a 120 m long span under a constant current-induced flow with the velocity of 0.7 m/s has been assessed. Results show that comparing with the fatigue life of a fixed span, the present method leads to an increase in the fatigue life by about ten times. Full article