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We report a kind of coiled-up meta-liners with nonuniform cross sections (CMNC), which can efficiently attenuate low-frequency sound waves under grazing flow with a deep subwavelength thickness (e.g., ∼λ/17 at 500 Hz). At a grazing flow Mach number of 0.26, the average transmission loss of the meta-liner is 12.6 dB at 500–1000 Hz, which is twice as much as that of a double-degree-of-freedom acoustic liner of the same size. Physically, the nonuniform cross-sectional distribution and significant cross-sectional area ratio enhances vortex shedding, thus resulting in severe acoustic energy dissipation. The excellent low-frequency acoustic attenuation performance of CMNC is investigated thoroughly with experimental, theoretical, and numerical methods. This work provides an avenue for low-frequency noise reduction in grazing flow scenarios (e.g., in a high bypass ratio turbofan engine). [ABSTRACT FROM AUTHOR]

Accurate prediction and comprehension of off-design turbine performance hold paramount importance in the development of highly efficient turbines capable of operating across a diverse range of conditions. This research concentrates on a highly loaded turbine cascade endwall flow and endeavors to scrutinize the impact of both incidence angle and inlet free stream turbulence intensity (FSTI). The investigation involves a meticulous analysis leading to substantial improvements in the existing endwall loss model (the Benner model correlated with the Moustapha incidence loss correction model), tailored for off-design scenarios. The findings underscore the pronounced influence of both incidence angle and FSTI on the dynamics of the endwall flow. Notably, alterations in the incidence angle have been identified as exerting a discernible impact on the flow structure, particularly when encountering large positive incidence angles. At an incidence angle of +20°, a distinctive vortex known as the Concentrated Shedding Vortex emerges as a pivotal factor in shaping the endwall flow structure, resulting in a substantial escalation in endwall losses. Furthermore, variations in FSTI predominantly affect the intensity of secondary vortices, thereby influencing endwall loss. Leveraging these discernments, an expressive formulation for endwall loss is derived by refining the higher-order terms of the incidence loss correction model and introducing a corrective term associated with FSTI. It has been validated that the proposed model controls the prediction error of endwall loss within a margin of ±0.02. [ABSTRACT FROM AUTHOR]

Centrifugal pump operation noise is an avoidable common phenomenon in engineering practices, and its characteristics are closely influenced by the flow characteristics of the fluid. In this paper, a numerical simulation of centrifugal pump operation with different flow rates is carried out using the detached eddy simulation turbulence model and compared with the experimental results. Then the noise source and far-field radiated noise characteristics of the centrifugal pump are investigated using Lighthill's analogy. The results show that the noise of centrifugal pump is closely related to the flow characteristics of impeller, especially the generation and development of vortex. The relationship between turbulent kinetic energy (TKE) and vortex is complex, involving the generation, development and shedding of vortex. The influence of flow rate variation on vortex structure in impeller is studied by vortex transport equation. It is found that the relative vortex stretching (RVS) term is the main driving force of vortex distribution. The distribution of the Coriolis force (CORF) term is mainly concentrated in the inlet and outlet areas of the flow channel, which is related to the rotational motion of the impeller and the dynamic characteristic of the fluid. The power spectral density inside the impeller is mainly concentrated in the low frequency region, indicating that the low frequency noise component is dominant in energy. The directivity curve of far-field noise pressure level is influenced by hydrodynamic effect, impeller rotation direction and pump design structure, and will have a certain deviation. The spectral curve analysis of velocity, vorticity, pressure and sound pressure level shows that these physical quantities have strong correlation on the spectrum, in which the low frequency component is large, and the high frequency component is complex and volatile. [ABSTRACT FROM AUTHOR]

In this paper, we describe numerical algorithms that can be used to solve the coupled fluid–structure interaction with incompressible viscous fluid. We characterized the fluid force effects over a circular cylinder attached to an elastic rod. To resolve the coupled governing equations, the velocity profiles are approximated with quadratic polynomials ( P 2 ), while the pressure is estimated using a different space with linear polynomials ( P 1 ) using the finite element method. The discrete systems are solved using a Newton method that employs split differences to explicitly generate the Jacobian matrices. This approach enables us to address the nonlinearities at each time step and apply direct, steady techniques. The inquiry's findings reveal a significant relationship between the behaviors related to steady streaming and the flow regimes associated with vortex shedding. In addition, at Re = 100, steady flow is characterized by minimal displacement and negligible oscillations. In contrast, the occurrence of larger oscillations at Reynolds numbers exceeding 140 suggests an increase in flow instability. [ABSTRACT FROM AUTHOR]

This study presents a thorough comparative analysis of non-cavitating and cavitating flows around a two-dimensional National Advisory Committee for Aeronautics airfoil (NACA) 0012 hydrofoil, focusing on flow behavior at different cavitation numbers while maintaining a constant Reynolds number. The experiments, conducted at Chungnam National University's cavitation tunnel, employ Particle Image Velocimetry to capture and analyze the flow dynamics under both regimes. The Reynolds number ranges from 5.8 × 105 to 7.2 × 105, with cavitation numbers (σ) ranging from 4.2 to 3.1 under cavitating conditions and 8.4 to 6.6 under non-cavitating conditions. The results indicated that cavitation substantially influences flow structures, forming re-entrant jets, intensifying shear zones, and increasing vortex shedding. As the cavitation length expands from 0.05 C to 0.4 C with decreasing σ, regions of heightened shear strain are observed between 0.2 and 0.65 C. The flow under non-cavitating conditions demonstrates smoother, more consistent behavior, with vortices concentrated near the trailing edge beyond 0.5 C. Detailed analyses of vector tracking, Q-criterion, and vorticity further clarify the complex interactions between cavitation and vortex dynamics, providing a comprehensive understanding of cavitating flows' turbulent behaviors and instabilities. This research offers new insights into the impact of cavitation on hydrofoil performance by maintaining a constant velocity while varying cavitation numbers. It contributes to a more profound understanding of cavitation phenomena and their implications for design and performance optimization in marine and industrial applications. These findings are essential for advancing mitigation strategies and enhancing the efficiency of hydrofoil-based systems in environments prone to cavitation. [ABSTRACT FROM AUTHOR]

Proximity of seabed complicates vortex-induced vibrations of submarine pipelines. Empirical models are better in engineering problem than high fidelity simulations and experiments to some extent. Present paper aims to propose a model consisting of structure and wake oscillators to predict in-line and cross-flow coupling vibration of a near-wall cylinder. Based on phenomena, mechanisms, and data analysis, some hydrodynamics, namely vortex shedding frequency and time-varying/time-averaged lift/drag coefficients, are modeled by Reynolds number, thickness of boundary layer, and gap (G) between cylinder and wall. Model responses reflect effects of the wall on the cylinder's vibration successfully. When G/D drops from 2 to 1 (D is diameter of the cylinder), amplitudes decrease monotonously, and the maximum amplitude shifts to a smaller reduced velocity (Ur). Vibrations and resonant tend to start/end at a larger/smaller Ur, leading to narrowing lock-in regions. Time-averaged transverse displacements increase monotonously in whole, while streamwise displacements drop in the resonance regime. Trajectories are shapes of symmetric "8," being similar to that of an isolated cylinder in free stream. There are some unique features when G/D decreases from 1 to 0.35. First peak of in-line vibration tends to disappear. Trajectories become asymmetric shape of "8" or oval because the cylinder tends to vibrate in approximating frequencies in 2 directions. With further researches on effects of wall proximity, improvements of hydrodynamics can be better to enhance model's rationality and accuracy. An accurate model is essential to analyze the safety and reliability of submarine pipelines suffering vibration. [ABSTRACT FROM AUTHOR]

The wake evolution behind a moving impenetrable obstacle potential in a defective Bose–Einstein condensate (BEC) loaded in a shallow optical lattice is investigated. Exploiting the linear stability analysis method and potential flow theory, we analytically calculate the stability condition and velocity of Kármán vortex street, which agrees well with the numerical results. Based on it, the effects of defect on the stability of the Kármán vortex street and vortex pair shedding frequency are studied. The findings suggest that the stability of the vortex street deteriorates with the increase in lattice depth; however, special lattice constants can improve stability. It is worth noting that the shedding frequency of vortex pairs linearly increases with the obstacle velocity. Moreover, the relationship between critical velocity and vortex street structure parameters is established based on different expressions of shedding frequency, which may provide a new method for critical velocity measurement. Additionally, we also find that the Strouhal number (St) effectively characterizes the vortex street generation range when the impenetrable obstacle potential through BEC, which is significantly different from St ≈ 0.21 in classical fluids. [ABSTRACT FROM AUTHOR]

Rectangular steel box girders offer advantages such as a simple frame, high stability, and strong bearing capacity. Despite their widespread use, these girders are susceptible to vortex-induced vibration (VIV), posing challenges to the wind-resistant design. This study aims to comprehensively understand the VIV characteristics of different rectangular steel box girders, based on which effective VIV suppression measures are proposed. First, the rectangular box girders with aspect ratios of 4:1, 6.7:1, and 9:1 are selected to investigate the VIV performance through sectional model wind tunnel tests. The test results reveal significant differences in VIV characteristics among the test sections. The section with the most pronounced vertical VIV is the model with an aspect ratio of 4:1. In contrast, the section with the most significant torsional VIV is the one with an aspect ratio of 9:1. The box section with an aspect ratio of 6.7:1 also exhibits noticeable vertical and torsional VIV responses. Subsequently, the wind tunnel test result regarding the suppression of VIV indicates that setting symmetrical wind fairings with 1/8 times the section width has varying effects for each aspect ratio section. Symmetrical wind fairings reduce the VIV amplitude of the box girder with aspect ratios of 4:1 and 9:1 under different wind attack angles but increase the VIV response of the box girder with an aspect ratio of 6.7:1 at 0°, +3°, and +5° wind attack angles. Finally, the computational fluid dynamics numerical calculations simulate the flow field of each testing section, determining the vortex shedding mode of the rectangular box section for each aspect ratio, both before and after setting the wind fairings. The research results can provide a reference for the aerodynamic design and aerodynamic measures to suppress VIV in long-span bridges. [ABSTRACT FROM AUTHOR]

Self-excited forces arise from the interaction between the structural vibration and the surrounding flow. While this phenomenon has been extensively studied, technical challenges in fabricating aeroelastic systems and synchronizing displacement, wind pressure, and flow measurements have limited simultaneous data. To improve understanding of the self-excited force mechanism, further experimental studies are needed. This study investigates the self-excited force and flow patterns around a transversely free-vibrating square-section cylinder in a low turbulence uniform flow. Displacement at the base of the model was measured using a laser sensor, while wind pressure on the sidewalls and flow at two-thirds of the cylinder height were measured with a multiple-point synchronous pressure system, along with the flow field measured by particle image velocimetry. The self-excited force mechanism was analyzed by examining the interaction between the cylinder's vibration and the surrounding flow. When the model's displacement has minimal effect on the flow, Karman vortex shedding occurs intermittently, with symmetric vortex shedding dominating the lift force fluctuations. During vortex resonance, Karman vortex shedding prevails, with strong compression between the shear layers and the large displacement of the model generating substantial lift and self-excited forces. [ABSTRACT FROM AUTHOR]

The undulating fin exhibits two distinct motion modes: undulation and oscillation. However, the hydrodynamic performance during oscillatory motion has been rarely reported. In this study, numerical simulations were conducted to investigate the effects of factors such as the undulating angle, oscillation angle, and oscillation frequency on the hydrodynamic performance of the undulating fin during oscillatory motion. The mechanism of undulating fin oscillation was elucidated through flow field analysis. The results demonstrate that the undulating fin achieves unilateral movement during a single oscillation cycle. The hydrodynamic performance in the X-direction exhibits non-sinusoidal characteristics and shows a positive correlation with the undulating angle. In contrast, the hydrodynamic performance in the Y-direction correlates positively with both the oscillation angle and frequency. The hydrodynamic performance in the Z-direction is closely related to the vortex shedding position. Positive thrust is generated when the vortex sheds from the outer side of the undulating fin. This study provides novel insights and motion strategies for underwater locomotion of robots equipped with undulating fins. [ABSTRACT FROM AUTHOR]

The aerodynamic interference effects between tandem structures are significant and can adversely affect both the wind-induced vibration characteristics and the aerodynamic performance. To investigate these effects, wind tunnel tests and numerical analyses were performed on chamfered and non-chamfered rectangular sections. Different spacings 2.9B–5.0B (B represents section width) were considered. Wind tunnel tests evaluated the vortex-induced vibrations (VIV) amplitude and wind speed range. Numerical analyses examined the aerodynamic characteristics and flow structure. It indicates that chamfered corners can enhance the VIV performance of a single structure. While the maximum VIV amplitude in the upstream column with chamfered corners, at spacing of 2.9B, increases by 288% than that of a single section, and gradually decreases as the spacing increases. The maximum VIV amplitudes of upstream rectangular section are slightly increased. For downstream section, the maximum VIV amplitude is much smaller than that of a single section. The mean drag coefficient of downstream cylinder consistently remains lower than that of upstream section, although it slightly increases with larger spacing. Chamfered corners cause upstream wake vortices to contract and downstream wake vortices to elongate along the flow direction. At spacing 2.9B, vortices shed from the upstream section just impact the windward side of downstream section. Compared to the upstream section, the vortex core center of the downstream column section is closer to its leeward surface, and the recirculation length is shorter than that of the upstream section. The research findings can serve as a reference for wind-resistant design of similar structures. [ABSTRACT FROM AUTHOR]

Although various structural modifications of the impeller and volute are employed to suppress flow-induced noise, few such modifications focus on the relationship between the generation and the variation of flow and noise. Herein, the spatiotemporal evolution of vortex structure and noise source in impeller and volute is investigated by vortex sound theory and spectral proper orthogonal decomposition (sPOD). The results show that the tip leakage vortex (TLV) formed near the blade leading edge is a significant noise source. As the TLV develops into a passage vortex, the strength of noise source gradually decreases. Within the passage, the noise source at 90% span attenuates because of the interaction between shed vortices, whereas the noise at 50% span is due to the spatial interaction of noise source. Furthermore, the variation of entropy production correlates with noise source. In the near-tongue region, the dominant rotation frequency and second blade passing frequency (2BPF) are obtained by sPOD, which reveals that the jet wake is extracted at 2BPF and flow patterns featuring strip-like structures appear. Correspondingly, the noise source forms a multiscale dotted distribution near the blade trailing edge (BTE). In comparison with original BTE, the wavy BTE effectively suppresses the multiscale pattern of noise source generated from the BTE at rotation frequency and 2BPF, with a decrease in about 20.75% and 8.35% in the total energy of the two leading modes. However, the characteristics of noise source near the tongue remain unchanged. These findings provide meaningful insights into the noise reduction of centrifugal pump. [ABSTRACT FROM AUTHOR]

Studying the energy loss characteristics of the electrical submersible pump (ESP) under stalling conditions is beneficial for reducing the global carbon emissions. By combining steady and unsteady numerical simulations with entropy production (EP) theory, the evolution of internal vortices in the ESP under stalling conditions is analyzed, and a theoretical model for predicting energy loss based on EP is established. The results show that turbulent dissipation entropy production inside the ESP is the main component of total entropy production. Under critical stall conditions, the stability of vortices inside the impeller of a single-stage ESP is higher. However, in the first-stage impeller of a multi-stage ESP, the periodic shedding and breakdown of vortices lead to a turbulent flow field at the inlet of the diffuser, resulting in increased impact losses. Under deep stall conditions, the inlet recirculation vortices in the impeller of a single-stage ESP exhibit a symmetric distribution. In multi-stage pumps, the evolution period of inlet recirculation vortices is asynchronous with the impeller rotation period. There are differences in the shedding period of vortices in each flow channel, resulting in nonsymmetrical distributions of vortices in the circumferential and radial directions. The interaction between the outlet vortices of the diffuser and the passage vortices leads to the formation of multiple high-energy, small-scale vortex structures at the entrance to the next-stage impeller. It will further lead to fluid separation and cause the next-stage impeller to enter a stall condition. The research results offer valuable insights that can be utilized as references for optimizing design and field application of ESPs. [ABSTRACT FROM AUTHOR]

The complete dynamic stall process encompasses a series of complex developmental stages, such as flow separation, leading edge vortex shedding, and reattachment. Unlike static stall, dynamic stall exhibits hysteresis, rendering phenomenological models as complex nonlinear state-space systems, often accompanied by numerous empirical parameters, which complicates practical applications. To address this issue, the Goman–Khrabrov (G-K) dynamic stall model simplifies the state space and retains only two empirical parameters related to time delays. Our study finds that different developmental stages of dynamic stall exhibit various time delay scales. The G-K dynamic stall model, which utilizes a first-order time-invariant inertia system, forcibly unifies the time scales across different stages. Consequently, this leads to intractable nonphysical modeling errors. This paper introduces the latest revised G-K model that employs a time-varying state space system. This model not only maintains a concise form but also eliminates the nonphysical modeling errors previously mentioned. In response to the challenge of identifying empirical parameters, this paper presents a parameter identification method for both the original and revised G-K models utilizing a Physics-Informed Neural Network. The revised model was validated through dynamic stall load prediction cases for mild, moderate and deep dynamic stall on various airfoils, achieving a maximum accuracy improvement of up to 74.5%. The revised G-K model is capable of addressing a broader range and more complex practical applications. [ABSTRACT FROM AUTHOR]

The present study investigates the impact of bulk viscosity on the complex flow dynamics past a rotating cylinder, with particular emphasis on compressible and non-equilibrium effects that emerge in nitrogen (N 2) and carbon dioxide (CO 2). By solving unsteady conservation laws obtained from the Boltzmann–Curtiss transport equation, the research focuses on key flow features such as vortex shedding, vorticity generation, enstrophy, kinetic energy dissipation, and the degree of thermal non-equilibrium. Numerical simulations are performed at a Mach number of 0.6 using the dbnsTurbFoam solver with unstructured meshes, and the computational model is verified using available data for flow past a rotating cylinder. The results reveal that bulk viscosity significantly affects vortex shedding, particularly suppressing vortex formation and reducing flow instability. In CO 2 , high bulk viscosity nearly eliminates vortex shedding, leading to a laminar wake, while in N 2 , vortex shedding is dampened but persists. Enstrophy and vorticity production through stretching and baroclinic effects are also reduced in both gases as bulk viscosity increases, with CO 2 showing more dramatic reductions due to its higher inherent viscosity. The study further indicates that bulk viscosity enhances kinetic energy dissipation in both gases, with N 2 exhibiting sharper dissipation than CO 2 . Additionally, the role of rotational speed is explored, showing that higher rotational speeds amplify vorticity production and energy dissipation. While high-speed rotation induces more turbulence and instability in N 2 , it stabilizes the flow in CO 2 , leading to a more organized wake. The findings demonstrate that bulk viscosity and rotational speed are crucial in controlling flow stability and energy dissipation, with significant variations depending on the gas properties. [ABSTRACT FROM AUTHOR]

The present research aims to study cavitating flow around a CLARK-Y 11.7 % hydrofoil with variable angles of attack (α) while maintaining controlled levels of dissolved air in the operating fluid, which is water. A series of experiments were conducted using a water tunnel facility, where the cavitation characteristics were measured and observed using sensors and high-speed imaging techniques. The variables studied in the present work are cavitation number (1 ≤ σ ≤ 2.2) and angle of attack (α = 4°, 6°, 8°, 10°, and 12°), with dissolved air levels (DAL) in the range of 9.3 ppm to 13.1 ppm. The dimensionless cavity length decreases significantly with increasing values of σ/α, indicating an inverse relationship where higher cavitation numbers or lower angles of attack result in shorter cavities. The cavity length follows a power-law scaling relationship, with the empirical equation L max / C = 4.78 × σ / α − 0.76.Increasing the angle of attack transitions the cavitation nature from stable (Mode I) to dynamic (Mode II) and highly oscillating (Mode III). Larger cavities result in lower Strouhal numbers, which indicates reduced vortex shedding activity. The relationship between the Strouhal number and the normalized cavitation number σ/α is characterized by the power-law equation St = 0.041 × σ / α 0.3 . The pressure coefficient at the leading-edge increases with the angle of attack at low cavitation numbers, while higher cavitation numbers lead to greater pressure coefficient differences between the leading and trailing edges. The present study offers an extensive dataset and empirical correlations that may serve as a benchmark framework, which facilitates the validation of computational and experimental models of cavitating flow under similar conditions. [ABSTRACT FROM AUTHOR]

The study delves into the dynamic behavior of fluid flows in hydrodynamic (HD) and magnetohydrodynamic (MHD) regimes, specifically focusing on the influence of varying magnetic field strengths on vortex shedding around a cylinder. Employing advanced modal decomposition techniques such as Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD), the research unveils the intricate characteristics of these flow fields. In HD scenarios, the flow exhibits complex, periodic patterns with notable vortex shedding, whereas in MHD scenarios, the introduction of magnetic fields gradually transforms the flow into a more stable and streamlined state. The study significantly demonstrates the damping effect of magnetic fields on vortex intensity and oscillations, leading to a uniform flow at higher field strengths. This study leverages DMD to predict future flow dynamics in both HD and MHD regimes around a cylinder. By using snapshots from CFD simulations at Re = 120, we validate DMD's predictive capabilities by comparing predicted snapshots with CFD results at corresponding time instants. This approach not only demonstrates DMD's robustness in capturing complex flow behaviors but also highlights its potential for real-time monitoring and control in industrial applications. The findings provide new insights into the temporal dynamics of MHD flows and open avenues for optimizing flow control strategies in engineering systems. [ABSTRACT FROM AUTHOR]

A falling powder can generate a dust cloud from its interaction with the ambient air and from its splash onto a substrate. This article reports the results of a numerical simulation study, which attempts to model this second process. We argue that the dust cloud arises from the aerodynamic resuspension of previously deposited small particles. The agglomerated falling powder is modeled as a falling pellet disk impacting a surface covered with a monolayer of previously deposited particles. The Reynolds number of the air flow in the vicinity of the impacting pellet is Re ∼ 1860, so the air flow is modeled as laminar and incompressible. The dust particles are incorporated via a Lagrangian multiphase treatment. The sudden deceleration of the disk sheds an aerodynamic vortex, which suspends particles from the monolayer. Characteristics of the dust cloud (average and maximum height and radius) are tracked; these are conveniently summarized by following the trajectory of the dust cloud centroid. The probability of aerosolization decreases with distance from the impacted pellet. The centroid trajectory is studied as a function of dust particle size. The model is relatively insensitive to disk radius and thickness. More realistic modeling of dust clouds generated by the splash of falling powders will require a statistical analysis of aggregate size and location, as well as the inclusion of interparticle and particle-surface interactions. [ABSTRACT FROM AUTHOR]

The lower semi‐open box (LSOB) girder is widely used in large‐span bridges due to its favorable stress performance and cost‐effectiveness. The vortex‐induced vibration (VIV) of the LSOB girder was studied by using a 1:55 section model wind tunnel test. The test results show that there are obvious vertical and torsional VIV intervals with significant amplitudes at each angle of attack with the damping ratios of about 0.35%. The CFD numerical simulations indicate that VIVs of LSOB girders are mainly induced by two types of vortices: one at the inclined webs of leeward wind nozzles and another at the upstream upper surfaces of the deck. Conventional aerodynamic vibration suppression measures, such as the lower central stabilizing plate and the guide vane at the gantry rail, demonstrate that the lower central stabilizing plate can reduce the VIV response at all wind angles of attack, decreasing vertical amplitude by 40%–50% and torsional amplitude by 10%–25%. Although adding a guide vane further optimizes the VIV performance, its effect is limited. Installing the lower central stabilizing plate helps redistribute vortices below the girder, transforming large vortices into smaller ones, most of which do not detach, thereby reducing vortex shedding intensity in the wake area. The bilateral guide vanes at the maintenance car track further weaken the wake vortices at the diagonal webs on the leeward side. [ABSTRACT FROM AUTHOR]

The document delves into wake-induced vibration (WIV) on a circular cylinder downstream of an oscillating cylinder, revealing a shift to 'wake-captured vibration' with large-amplitude oscillations. The study uncovers a negative correlation between upstream vortex-induced vibration and downstream WIV responses. Through controlled experiments, researchers map hydrodynamic properties and investigate the interference mechanism of upstream oscillation on downstream WIV response. The collection of research articles explores flow-induced vibrations of tandem cylinders, shedding light on complex fluid-structure interactions in various flow conditions and engineering applications. [Extracted from the article]

The article in the Journal of Fluid Mechanics explores the linear stability analysis of turbulent mean flows around an airfoil, specifically focusing on predicting three-dimensional stall cells. By using global stability analyses of turbulent mean flows computed with Reynolds-averaged Navier-Stokes equations, the study investigates corrections to turbulence models to enhance mean flow estimation. The research highlights the significance of data assimilation in improving predictions of flow separation and recirculation regions near the airfoil's trailing edge, ultimately leading to a more precise representation of flow behavior and the onset of stall cells. The study underscores the importance of selecting the appropriate correction for turbulence models in stability analyses, with correction ¯f1 demonstrating the most accurate predictions of stall cell onset. [Extracted from the article]

The document explores the use of large-eddy simulation (LES) and the regularized ensemble Kalman method for shape optimization to reduce turbulent wakes behind bluff bodies. The study showcases the effectiveness of the ensemble-based method in optimizing the shape of a cylinder to minimize turbulent kinetic energy in the wake flow region. Additionally, the document includes a collection of research articles covering various topics related to sensitivity analysis, turbulence modeling, and large-scale field inversion in computational fluid dynamics, contributing to the advancement of computational methods in fluid dynamics. [Extracted from the article]

The article "Influence of three-dimensionality on wake synchronisation of an oscillatory cylinder" in the Journal of Fluid Mechanics examines how three-dimensionality affects the synchronization of wakes behind an oscillating circular cylinder. Using phase-reduction analysis, the study compares the synchronizability of different cylinder oscillations and finds that three-dimensional wakes have lower phase-sensitivity functions, making synchronization with weak cylinder oscillations more challenging. The research suggests that phase-reduction analysis can be a valuable tool for studying synchronization in complex fluid flows, shedding light on the dynamics of wake synchronization in fluid dynamics. [Extracted from the article]

The article "Free-surface effects on the flow around two circular cylinders in tandem" delves into the impact of a free surface on the flow dynamics of two circular cylinders in tandem. The study, conducted through numerical simulations at a Reynolds number of 180, identifies various flow regimes, including trailing wakes, single vortex shedding wakes, and co-shedding wakes. The research highlights the influence of the free surface on wake patterns, hydrodynamic forces, and free-surface deformations, revealing complex interactions between the flow structures and the free surface in the wake of the cylinders. [Extracted from the article]

The article explores an experimental study on data-driven active control of a thin elliptical cylinder experiencing transverse flow-induced vibrations. By implementing axial flapping motions using Bayesian optimization, researchers were able to maximize vibration amplitudes and uncover two new synchronization regimes not previously reported. The findings have implications for energy extraction from water sources, shedding light on the coupling between vortex-induced vibration and galloping-like movement-induced instability. The study delves into the effects of axial rotation on wake-body synchronization and vibration amplitudes, identifying distinct regimes and analyzing control parameters for optimal performance. [Extracted from the article]

This study investigates the impact of a rotating tube on the flow characteristics within a tube bank consisting of nine cylinders arranged in an in-line configuration, with a pitch-to-diameter ratio of 1.44, using both experimental and numerical approaches. Experiments are performed in a subsonic wind tunnel to measure pressure distributions at various azimuthal angles along the tubes, using a multi-channel differential pressure system. Drag forces are determined via a wire-strain gauge balance. Numerical simulations are conducted using ANSYS Fluent, employing the URANS-based Shear-Stress Transport (SST) k–ω model, to replicate turbulent cross-flow at two values of Reynolds numbers Re=0.712×105 and Re=1.42×105. This study explores the effect of a tube rotation within the array on flow separation angles, pressure distributions and vortex shedding in the wake region, focusing on the effects of different positions of the rotating tube on the flow characteristics of the surrounding tubes. Numerical results closely match the experimental data, demonstrating that the rotational motion significantly mitigates flow separation and reduces drag forces on adjacent tubes. Additionally, the position of the rotating tube within the array plays a critical role in optimizing the fluid forces and pressure distribution, offering enhanced control over the flow within tube banks. [ABSTRACT FROM AUTHOR]

A slab‐type high‐rise residential building with a depth‐to‐width ratio exceeding 6 was studied. Multi‐point surface pressure measurements and high‐frequency force balance (HFFB) wind tunnel tests were conducted to investigate the wind‐induced dynamic characteristics of the building. The dynamic responses, especially accelerations closely related to serviceability performance, were determined and examined in both time and frequency domains. The spectral properties of the time‐history acceleration responses were compared with frequency‐domain results. Analyses showed acceleration responses were amplified when along‐wind or across‐wind directions aligned with the shorter building axis. The slab‐type cross‐section reduced vortex shedding in the across‐wind direction. As a result, peak accelerations were often dominated by along‐wind excitations. Torsional accelerations approached those induced by along‐wind winds, likely due to both fundamental and higher modes. [ABSTRACT FROM AUTHOR]

The article discusses the fluid mechanics of active flow control at large scales, focusing on the impact of wake interactions between wind turbines on power output. Research on using yawed wind turbines for active flow control has led to insights and modeling developments. The study highlights the importance of understanding wake deflection and its impact on downstream turbines. Various follow-up studies have explored the implications of yawed wind turbines on power production and the development of wake deflection models for optimization. The article emphasizes the need for further research on dynamic models for yawing turbine wakes and the potential for future extensions in offshore wind energy applications. [Extracted from the article]

The document explores the hydrodynamic interactions and performance benefits of two pitching foils swimming in a side-by-side formation, achieving stable equilibrium positions with increased speed and efficiency. The findings suggest that swimming in a slightly staggered formation leads to optimal performance, offering insights into passive stability and performance of schooling swimmers for biological and robotic applications. The research collection covers various aspects of aquatic locomotion, including propulsive wakes, fish swimming characteristics, vortex control for foil propulsion, and deep reinforcement learning for collective swimming, published online by Cambridge University Press. [Extracted from the article]

The study delves into the wake dynamics of wind turbines in unsteady streamwise flow conditions, aiming to understand the impact of dynamic forcing on wake recovery and available power downstream. Through experiments in a towing-tank facility, researchers observed significant improvements in wake recovery compared to steady-flow cases, highlighting the potential to enhance power density in wind farms. The study also explores the effects of nonlinear travelling waves on wind-turbine wakes and emphasizes the importance of dynamic models in understanding the full dynamics of unsteady wakes. Additionally, the document discusses various aspects of wind turbine dynamics, including tidal turbine blades, wind turbine surge motion, and computational fluid dynamics analyses of floating offshore wind turbines. [Extracted from the article]

The article "Turbulent/turbulent entrainment in a planar wake" in the Journal of Fluid Mechanics explores the spatial evolution of turbulent entrainment in the wake of a circular cylinder under different turbulent backgrounds. The study reveals the establishment of two layers with distinct physical mechanisms and thicknesses, influenced by the local Kolmogorov length scale and background turbulence intensity. It delves into the dynamics of inhomogeneous dissipation and vorticity layers, focusing on turbulent/turbulent interfaces and turbulent/non-turbulent interfaces. The research also investigates the intermittent nature of entrainment velocity and its connection to intense enstrophy structures near the interface, raising questions about universal features and extreme entrainment events. The document includes references to related studies on turbulent flows, mixing dynamics, and fluid mechanics, offering a comprehensive overview of research in the field. [Extracted from the article]

The article "Path instabilities of freely falling oblong cylinders" delves into numerical simulations of the behavior of falling cylinders with varying length-to-diameter and density ratios. It identifies two transitional states, fluttering and weakly oscillating, influenced by the interplay of solid and fluid modes. The research sheds light on the scatter of drag coefficient values and oscillation frequencies, proposing correlations to fit simulation results. By exploring the complexities of path instabilities and fluid dynamics, the study contributes to a deeper understanding of the behavior of oblong cylinders in transitional regimes. [Extracted from the article]

The study in the Journal of Fluid Mechanics delves into the interaction of propeller tip vortices with turbulent boundary layers, examining changes in velocity profiles and turbulence statistics. Different tip clearances are analyzed, revealing effects on boundary layer dynamics such as reductions in the log region extent and enhancements in wake parameters. The research offers insights into the intricate relationship between propeller tip vortices and turbulent boundary layers, emphasizing the significance of understanding these dynamics for advanced hybrid propulsion systems. Future studies could benefit from incorporating wall static pressure measurements to further enhance comprehension of the flow state. [Extracted from the article]

The article in the Journal of Fluid Mechanics delves into the linear stability and spectral modal decomposition of the turbulent wake flow behind a high-speed train. Using spectral proper orthogonal decomposition (SPOD), the study uncovers dominant symmetric structures with periodic vortex shedding and wave-like patterns. The research also delves into the stability of the wake flow through two-dimensional local linear instability analysis, shedding light on coherent structures, vortex dynamics, and wake mechanisms. The study offers valuable insights into the dynamics and instability of turbulent wake flows, emphasizing the significance of global modes and their impact on train surface fluctuations. [Extracted from the article]

The article explores the use of harmonic resolvent analysis to study compressible cavity flows, emphasizing cross-frequency interactions. By applying this framework to linearized Navier-Stokes equations, the study uncovers the dominance of nonlinear cross-frequency interactions in perturbation amplification at different Mach numbers. The research validates the approach through low-Mach-number flow past an airfoil and extends its application to compressible cavity flows at Mach numbers of 0.6 and 0.8. The document also includes a collection of research articles on fluid mechanics, stability analysis, and flow control, offering valuable insights into fluid dynamics and control mechanisms. [Extracted from the article]