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A mesoscale model is used to systematically investigate how the incoming flow incidence angle affects the development of atmospheric von Kármán vortex streets for non‐axisymmetric islands. The analysis is focused on an event observed on the leeward side of Guadalupe Island. By keeping the synoptic conditions the same, several simulations are performed for rotated orientations of the island topography, which correspond to a change in the angle of attack (AoA) relative to the upstream flow. The asymmetry of the vortex shedding and the role of the leading and trailing edge are in line with what was observed in laboratory von Kármán vortex streets past a flat plate. The eddies become larger with increasing AoA while the shedding frequency decreases, and the asymmetry between cyclonic and anticyclonic eddies weakens. Cyclonic vortices are more developed and stronger under typical conditions when they are shed from the trailing edge. We also demonstrate that the wake asymmetry is fundamentally between trailing‐edge and leading‐edge eddies rather than between cyclonic and anticyclonic eddies. Plain Language Summary: Low‐level marine clouds in satellite images often reveal vortex streets formed by two rows of counter‐rotating vortices on the leeward side of isolated mountainous islands. This phenomenon is called the "atmospheric von Kármán vortex street" (AVKVS) and has been investigated by satellite observations, laboratory experiments, and numerical modeling. Past studies highlighted an asymmetry between clockwise and counterclockwise rotating vortices, which was attributed to elongated island shapes and the effect of the Coriolis force. However, the origin of the AVKVS asymmetry is not yet fully understood. We use a mesoscale model to evaluate the effect of the incoming flow incidence angle (or angle of attack, i.e., AoA) on vortex street morphology for an elongated island. We first realistically simulate a vortex street observed downstream of Guadalupe Island and then, by keeping the same meteorological conditions, we simulate the phenomenon with artificially rotated island orientations to modify the AoA. The results show that the dimension of the vortices increases but their asymmetry weakens with increasing AoA. We also demonstrate that the wake asymmetry is fundamentally between trailing‐edge and leading‐edge eddies rather than between cyclonic and anticyclonic eddies. Key Points: The mesoscale Weather Research and Forecasting model (WRF) is used to study the characteristics of atmospheric von Kármán vortex streets (AVKVS) behind an elongated islandWe have convincingly demonstrated that the wake asymmetry of an AVKVS decreases with increasing angle of attackThe wake asymmetry is fundamentally between trailing‐edge and leading‐edge eddies rather than between cyclonic and anticyclonic eddies [ABSTRACT FROM AUTHOR]

This study explores the feasibility of using an oscillating plate downstream of a cylindrical body to produce mechanical energy from a Von Kármán vortex street under sub-critical flow conditions (Re = 72,500). The study aims to quantify the impact of the plate length, its separation from the cylinder, and a machine damping factor on the power coefficient and the blade's displacement to identify the optimal configuration. This preliminary assessment assumes that the plate oscillation is small enough to avoid changes in the vortex dynamics. This assumption allows the construction of a surrogate model using Computational Fluid Dynamics (CFD) to evaluate the effect of plate length and separation from the cylinder on the fluctuating lift forces over the plate. Later, the surrogate model, combined with varying machine damping factors, facilitates the description of the device's dynamics through the numerical integration of an angular momentum equation. The results showed that a plate with a length of 0.52D, a separation of 5.548D from the cylinder, and a damping factor of 0.013 achieved a power coefficient of 0.147 and a perpendicular displacement of 0.226D. These results demonstrate a substantial improvement in the performance of blade-less generators. [ABSTRACT FROM AUTHOR]

It was experimentally observed that the front of a propagating flame of a well-mixed diluted methane-oxygen mixture at 298 K and 100–300 Torr does not form von Karman vortex shedding behind the obstacle of cylindrical shape of 30–50 mm in diameter, including a perforated cylinder; however, the instability under the same conditions occurs in the flow of hot products. In the perforated cylinder, the occurrence of local primary ignition centers on its inner surface is observed. In the mathematical modeling, the main observed features of the flame front propagation were taken into account: the chain branched mechanism of gaseous combustion and the absence of vortex shedding behind the obstacle at flame propagation. It was shown that a qualitative model of compressible dimensionless non-reactive/reactive Navier–Stokes equations in low Mach number approximation yields both the mode of the emergence of von Karman instability in chemically inert gas and the absence of the instability in the mode of flame propagation in a reacting flow. The model computations confirmed the occurrence of local primary ignition centers on the inner surface of the obstacle.

This study explores the feasibility of using an oscillating plate downstream of a cylindrical body to produce mechanical energy from a Von Kármán vortex street under sub-critical flow conditions (Re = 72,500). The study aims to quantify the impact of the plate length, its separation from the cylinder, and a machine damping factor on the power coefficient and the blade’s displacement to identify the optimal configuration. This preliminary assessment assumes that the plate oscillation is small enough to avoid changes in the vortex dynamics. This assumption allows the construction of a surrogate model using Computational Fluid Dynamics (CFD) to evaluate the effect of plate length and separation from the cylinder on the fluctuating lift forces over the plate. Later, the surrogate model, combined with varying machine damping factors, facilitates the description of the device’s dynamics through the numerical integration of an angular momentum equation. The results showed that a plate with a length of 0.52D, a separation of 5.548D from the cylinder, and a damping factor of 0.013 achieved a power coefficient of 0.147 and a perpendicular displacement of 0.226D. These results demonstrate a substantial improvement in the performance of blade-less generators.

Numerical simulations of fluid flows can produce a huge amount of data and inadvertently important flow structures can be ignored, if a thorough analysis is not performed. The identification of these flow structures, mainly in transient situations, is a complex task, since such structures change in time and can move along the domain. With the decomposition of the entire data set into smaller sets, important structures present in the main flow and structures with periodic behaviour, like vortices, can be identified. Therefore, through the analysis of the frequency of each of these components and using a smaller number of components, we show that the Proper Orthogonal Decomposition can be used not only to reduce the amount of significant data, but also to obtain a better and global understanding of the flow (through the analysis of specific modes). In this work, the von Kármán vortex street is decomposed into a generator base and analysed through the Proper Orthogonal Decomposition for the 2D flow around a cylinder and the 2D flow around two cylinders with different radii. We consider a Newtonian fluid and two non-Newtonian power-law fluids, with n = 0.7 and n = 1.3. Grouping specific modes, a reconstruction is made, allowing the identification of complex structures that otherwise would be impossible to identify using simple post-processing of the fluid flow. [ABSTRACT FROM AUTHOR]

The present study is a revisit to Ludwig Prandtl's elimination of von Kármán vortex street behind a circular cylinder by using steady suction in the boundary layer. We show in particular the full-time vortex evolutions and vortex dynamics in the wake. The wind tunnel investigations are conducted at the Reynolds number (Re) of 2.0 × 104. Slot suction is implemented symmetrically on both lower and upper boundary layers of the cylindrical test model to modify the flow separation process and to eliminate the downstream vortex street. The boundary layer suction is described by the dimensionless momentum parameter of suction relative to the free-stream airflow. A high-speed particle image velocimetry system is employed in the present study to visualize the flow patterns and capture the wake dynamics of the natural and modified cylinders controlled with boundary-layer suction. [ABSTRACT FROM AUTHOR]

• Impact of History force on particles distribution is investigated numerically. • For all cases presence of the history force suppresses the particle inertia. • History force increases particle clustering for large particles. • At moderate Stokes numbers history force decreases particle clustering. • Deposition rate of particles decreases when the history force is taken into account. Effects of the history (Basset) force on the dispersion of solid particles over a cylinder inside a two-dimensional channel flow associated with von Kármán vortex shedding are investigated. Particles with Stokes numbers ( St k) of 0.1, 0.5, 1.0 and 5.0 and particle-to-fluid density ratios of 1.1, 10 and 1000 are considered. Clustering (i.e. preferential concentration) of particles is studied qualitatively by visualising particle distributions, and quantitatively by analysing the preference of particles in sampling the vorticity field and by using Voronoϊ tessellation analyses. It is found that the effects of history force on the distribution of particles are noticeable only at moderate particle-to-fluid density ratios and Stokes numbers, though not very significant. Nonetheless, our results suggest that for flows with strong vortices the impact of the history force can be significant. It has also been observed for the first time that inclusion of the history force at high Stokes numbers, i.e. St k = 5.0 , can increase particle clustering at both moderate and high particle-to-fluid density ratios. At lower Stokes numbers, however, particle clustering decreases when the history force is taken into account. In general, the history force suppresses the influence of particle inertia in all the investigated cases. Finally, the deposition rate of particles, mainly on the front wall of the cylinder, decreases when the history force is included for all cases except when St k = 0.1. [ABSTRACT FROM AUTHOR]

Numerical simulations of fluid flows can produce a huge amount of data and inadvertently important flow structures can be ignored, if a thorough analysis is not performed. The identification of these flow structures, mainly in transient situations, is a complex task, since such structures change in time and can move along the domain. With the decomposition of the entire data set into smaller sets, important structures present in the main flow and structures with periodic behaviour, like vortices, can be identified. Therefore, through the analysis of the frequency of each of these components and using a smaller number of components, we show that the Proper Orthogonal Decomposition can be used not only to reduce the amount of significant data, but also to obtain a better and global understanding of the flow (through the analysis of specific modes). In this work, the von Kármán vortex street is decomposed into a generator base and analysed through the Proper Orthogonal Decomposition for the 2D flow around a cylinder and the 2D flow around two cylinders with different radii. We consider a Newtonian fluid and two non-Newtonian power-law fluids, with n=0.7 and n=1.3. Grouping specific modes, a reconstruction is made, allowing the identification of complex structures that otherwise would be impossible to identify using simple post-processing of the fluid flow.

To accelerate the integration of fluctuating renewable energy technologies in the power systems, it is necessary to increase the flexibility of hydropower by operating turbines at off-design conditions. Unfortunately, this strategy causes deleterious flow phenomena such as von Kármán’s vortices at the wake of the vanes and/or blades. When their shedding frequency lies in the vicinity of a structure’s natural frequency, lock-in occurs and vibration amplitudes increase significantly. Moreover, if cavitation occurs at the centers of these vortices, the structure’s dynamic response will be modified. In order to understand this interaction and to avoid its negative consequences, the vibration behavior of a NACA 0009 hydrofoil under a torsional lock-in condition was numerically simulated for cavitation-free and cavitating-flow conditions. The results showed that the presence of vortex cavitation modified the formation and growth process of shed von Kármán vortices in the near-wake region which, in turn, caused an increase of the work performed by the hydrofoil deformation on the surrounding flow and a sharp decrease of the maximum vibration amplitude under resonance conditions.

Two-dimensional incompressible fluid flow around a rectangular shape placed over a larger rectangular shape is analyzed numerically. The vortex shedding is investigated at different arrangements of the two shapes. The calculations are carried out for several values of Reynolds numbers from low values up to 52. At low Reynolds number, the flow remains steady. The flow characteristics are analyzed for each configuration. The analysis of the flow evolution shows that with increasing Re beyond a certain critical value, the flow becomes unstable and undergoes a bifurcation. It is observed that the transition to unsteady regime is performed by a Hopf bifurcation. The critical Reynolds number beyond which the flow becomes unsteady is determined for each configuration.

Three-dimensional numerical simulations, for confined flows and unconfined flows, have been carried out to study the Kármán vortex street inversion in the wake of a square cylinder. This paper is aimed to analyze the cause of the vortex inversion and to investigate the physical mechanisms. As two independent factors for the inversion, the wall confinement and the incoming flow conditions have been proved in a more rigorous way. It is shown that the interaction between the primary vortex and the incoming flow or the wall vortex layer is the fundamental cause. In order to compare the thermal transport phenomenon between the inversion and non-inversion cases, the top wall of a channel is kept at the free stream temperature and the bottom wall is set heated, while the cylinder is maintained adiabatic. The results indicate that the inversion phenomenon is not good for the heat transfer. Additionally, the effects of streamwise magnetic field on the vortex street inversion has been considered. [ABSTRACT FROM AUTHOR]

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A self-tuning fuzzy PID (ST-FPID) control scheme is implemented within a joint interactive (Matlab/Simulink/Fluent) co-simulation framework for effective two degrees of freedom (2DOF) vortex-induced vibration (VIV) control of an elastically-mounted circular cylinder in laminar cross-flow of incompressible non-Newtonian power-law fluids based on the control action of a single transverse force actuator. The model-free controller, which systematically tunes the control parameters online in real time based on given rules, is well-known to be highly advantageous over the previously employed conventional PID controllers. It is particularly capable of handling the intricate non-linear dynamic effects inherent in the complex fluid rheology of non-Newtonian flow past the cylinder in presence of unmodeled system dynamics, high parametric uncertainties, diverse operational conditions, and time-varying external disturbances and control signals. Extensive numerical simulations reveal that the complex shear-thinning and shear-thickening behaviors of fluid viscosity can substantially influence the cylinder dynamic response, applied hydrodynamic forces, and flow structure. In particular, effectiveness and high performance of the adopted ST-FPID control strategy in substantial suppression of the high amplitude coupled 2DOF VIV of the elastically-mounted cylinder at selected critical reduced velocities in the lock-in region are established for a wide range of power-law index parameters (e.g., up to 83% reduction in RMS value of cylinder cross-flow displacement and up to 35% reduction in RMS value of cylinder in-line displacement for n= 1and U* = 5 at Re = 100). Also, the vigorous action of the error-driven ST-FPID controller in forcing the high strength vortex shedding patterns of the uncontrolled cylinder out of the lock-in condition into the classical von Kármán vortex street of 2S-type mode of moderately weaker strengths is verified. • Two DOF-VIV co-simulation for an elastic cylinder in non-Newtonian power-law flow. • 1st model-free self-tuning fuzzy PID-VIV control for wide range of power law index. • Analysis of shear-thinning/thickening effects on cylinder VIV in the lock-in region. • A real-time interactive co-simulation framework linking MatlabSimulink with Fluent. [ABSTRACT FROM AUTHOR]

An exegesis of a novel mechanism leading to vortex splitting and subsequent shedding that is valid for two-dimensional incompressible, inviscid or viscous, and external or internal or wall-bounded flows, is detailed in this research. The mechanism, termed the vortex shedding mechanism (VSM) is simple and intuitive, requiring only two coincident conditions in the flow: (1) the existence of a location with zero momentum and (2) the presence of a net force having a positive divergence. Numerical solutions of several model problems illustrate causality of the VSM. Moreover, the VSM criteria is proved to be a necessary and sufficient condition for a vortex splitting event in any two-dimensional, incompressible flow. The VSM is shown to exist in several canonical problems including the external flow past a circular cylinder. Suppression of the von Kármán vortex street is demonstrated for Reynolds numbers of 100 and 400 by mitigating the VSM. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new methodology for numerically solving elliptic and parabolic equations with discontinuous coefficients and singular source terms. This new scheme is obtained by clubbing a recently developed higher-order compact methodology with special interface treatment for the points just next to the points of discontinuity. The overall order of accuracy of the scheme is at least second. We first formulate the scheme for one-dimensional (1D) problems, and then extend it directly to two-dimensional (2D) problems in polar coordinates. In the process, we also perform convergence and related analysis for both the cases. Finally, we show a new direction of implementing the methodology to 2D problems in cartesian coordinates. We then conduct numerous numerical studies on a number of problems, both for 1D and 2D cases, including the flow past circular cylinder governed by the incompressible Navier-Stokes equations. We compare our results with existing numerical and experimental results. In all the cases, our formulation is found to produce better results on coarser grids. For the circular cylinder problem, the scheme used is seen to capture all the flow characteristics including the famous von Kármán vortex street. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Two-dimensional incompressible fluid flow around a rectangular shape placed over a larger rectangular shape is analyzed numerically. The vortex shedding is investigated at different arrangements of the two shapes. The calculations are carried out for several values of Reynolds numbers from low values up to 52. At low Reynolds number, the flow remains steady. The flow characteristics are analyzed for each configuration. The analysis of the flow evolution shows that with increasing Re beyond a certain critical value, the flow becomes unstable and undergoes a bifurcation. It is observed that the transition to unsteady regime is performed by a Hopf bifurcation. The critical Reynolds number beyond which the flow becomes unsteady is determined for each configuration. [ABSTRACT FROM AUTHOR]

For over 100 years, laboratory-scale von Kármán vortex streets (VKVSs) have been one of the most studied phenomena within the field of fluid dynamics. During this period, countless publications have highlighted a number of interesting underpinnings of VKVSs; nevertheless, a universal equation for the vortex shedding frequency ( $$N$$ ) has yet to be identified. In this study, we have investigated $$N$$ for mesoscale atmospheric VKVSs and some of its dependencies through the use of realistic numerical simulations. We find that vortex shedding frequency associated with mountainous islands, generally demonstrates an inverse relationship to cross-stream obstacle length ( $$L$$ ) at the thermal inversion height of the atmospheric boundary layer. As a secondary motive, we attempt to quantify the relationship between $$N$$ and $$L$$ for atmospheric VKVSs in the context of the popular Strouhal number ( $$Sr$$ )-Reynolds number ( $$Re$$ ) similarity theory developed through laboratory experimentation. By employing numerical simulation to document the $$Sr{-}Re$$ relationship of mesoscale atmospheric VKVSs (i.e., in the extremely high $$Re$$ regime) we present insight into an extended regime of the similarity theory which has been neglected in the past. In essence, we observe mesoscale VKVSs demonstrating a consistent $$Sr$$ range of 0.15-0.22 while varying $$L$$ (i.e, effectively varying $$Re$$ ). [ABSTRACT FROM AUTHOR]

Theodore von Kármán's original two papers on the vortex street, written in Germa, are presented in the English translation. Both papers appeared under the same title “Über den Mechanismus des Widerstandes, denein bewegter Körper in einer Flüssigkeit erfährt“ 14 September and 23 December 1911. To the author's knowledge the papers were never translated into English. Following a request of the editor Professor Max Platzer, their translation is given in the following. [ABSTRACT FROM AUTHOR]

This study analyzes the flow over a two-dimensional (2D) circular cylinder at a turbulent Reynolds number of 20,000 and its control by air blowing from several slots located on the surface of the cylinder, computationally. CFD simulations are performed by using Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations and Spalart-Allmaras turbulence model. Uncontrolled flow simulation results are validated using the experimental results available in literature for drag coefficient, Strouhal number, time-averaged pressure coefficient distribution on the circumference of the cylinder and mean velocity values at the downstream. Air blowing from several slots located on the cylinder is used as an actuator for forcing the flow. Blowing from four slots located on the circumference of the cylinder with a velocity magnitude of 50% of the free stream velocity yields a drag reduction of 23% compared to the uncontrolled case. Additionally, near wake region is further examined by application of Proper Orthogonal Decomposition (POD) technique. A Fast Fourier Transform (FFT) based spatial filtering procedure is employed in order to separate the effects of small-scale turbulent structures in the wake region. The FFT-filtered snapshot-based POD analysis shows that approximately 99% of the total energy of the flow can be represented by considering only the most energetic first two modes where the effects of yon Karman vortex street can be seen appropriately both for uncontrolled and controlled flow cases. [ABSTRACT FROM AUTHOR]

A conformal mapping of the well-known VON KARMAN's "vortex street" provides an interesting inviscid analog of a plane liquid jet diffusing into a plane, quiescent liquid space. The asymmetric motion field represented by this formulation is generated from a velocity potential and as such it is generally irrotational, except for the presence of a multitude of concentrated eddies which, after issuing from a point source, are carried along by the general motion. The paper presents the main features of this analytical model, which suggest the conjecture that it could have some physical significance for the near-field of a diffusing jet. In the far-field, of course, the decaying of the concentrated vorticities to smaller and smaller scales leads to the onset of turbulent shear layers along the frontiers of the jet, so that for these distant regions the physical admissibility of the proposed inviscid model of the field of motion is invalidated. [ABSTRACT FROM AUTHOR]

Abstract: Forced convection heat transfer from two and three isothermal circular cylinders in tandem arrangement is studied numerically. In addition, the flow field and the vortex shedding behavior in the wake of the cylinders are investigated. The governing equations consist of continuity, momentum and energy equations are solved for laminar unsteady flow regime. The numerical simulations are performed with a developed finite volume code using the overset grid method. A general orthogonal boundary fitted coordinate system is used for the grid generation. This simulation is performed for the Prandtl numbers of 0.7 and 7 at the Reynolds numbers of 100 and 200. The spacing ratio L/D is set at 2, 3, 4, 5, 7 and 10. In order to analyze the heat transfer from isothermal cylinders, the mean and local Nusselt numbers and isotherm plots are presented and discussed for different values of the problem parameters. In addition, the mean and instantaneous drag and lift coefficients and Strouhal numbers are computed to elucidate the role of the Reynolds number and spacing ratio. Furthermore, two new correlations for the calculation of the mean Nusselt number, in terms of the spacing ratio and the Reynolds and Prandtl numbers, is proposed. In order to validate the solution, the obtained results are compared with available results in the published literature. [Copyright &y& Elsevier]

In this work, mesoscopic modeling via a computational lattice Boltzmann method (LBM) is used to investigate the flow pattern phenomena and the physical properties of the flow field around one and two square obstacles inside a two-dimensional channel with a fixed blockage ratio, β=1/4, centered inside a 2D channel, for a range of Reynolds numbers (Re) from 1 to 300. The simulation results show that flow patterns can initially exhibit laminar flow at low Re and then make a transition to periodic, unsteady, and, finally, turbulent flow as the Re get higher. Streamlines and velocity profiles and a vortex shedding pattern are observed. The Strouhal numbers are calculated to characterize the shedding frequency and flow dynamics. The effect of the layouts or configurations of the obstacles are also investigated, and the possible connection between the mixing process and the appropriate design of a chemical mixing system is discussed. [ABSTRACT FROM AUTHOR]

In the past it was found experimentally and numerically that eddy shedding on trailing edges of turbine aerofoils has significant effect on the aerodynamic performance. Aerofoils of gas turbines usually have relatively thick trailing edges for reasons of mechanical integrity, and hence strong unsteady wakes are created. The current investigation considers trailing edges without cooling injection; hence the area of application is limited to the low- and medium-pressure stages of a gas turbine. In this work a numerical investigation is performed with the aim to weigh the loss production inside these unsteady wakes against the available kinetic energy of the unsteady fluid to formulate a so-called unsteady recovery factor. Furthermore, several design exercises are presented on a gas-turbine rotor profile, which is interacting with the unsteady wake of an upstream vane with eddy shedding. This shows that the stage performance is quite significantly influenced comparing frontloaded, midloaded, and aftloaded profile designs in contradiction to standard steady design approaches. It was found that a frontloaded rotor design under consideration of interaction with an unsteady wake can increase the stage performance of a two-dimensional midsection considerably, while under steady assumptions it has about the same or worse performance. This result shows the importance of unsteady methods in turbine design and also potential new ways for improved profile design. [ABSTRACT FROM AUTHOR]

Feedback flow control of a three-dimensional wake behind a circular cylinder at a Reynolds number of Re = 100 was investigated. A combination of numerical simulations, experiments, and control theory was used to understand the flow field and to develop a sensor configuration, a flow state estimator, and a controller. The flow field was analysed by using proper orthogonal decomposition (POD) in two dimensions, and two-dimensional and three-dimensional sensor placements were investigated. The controller input was computed from the POD time coefficients, and actuation was performed by using rigid cylinder motion normal to the free stream. In the two-dimensional computations, feedback was shown to effectively reduce the drag and the fluctuating lift force. When feedback forcing was applied in the three-dimensional wake, both simulations and experiments showed that the vortex shedding could be controlled initially and the amplitude of the fluctuations decreased. However, spanwise phase variations eventually appeared and rendered the controller ineffective. [ABSTRACT FROM AUTHOR]

A delay based artificial neural network is used to analyze turbulent flow signals obtained by a hot wire anemometer along time in different points within the wake of a circular cylinder. Values of the Reynolds number range from 2000 to 8000, corresponding to late transitional or fully turbulent wake flows. The implemented trainable delay based artificial neural network is able to autonomously obtain the embedding dimension as well as the normalized embedding delay and permits performing short and long term predictions. The short term predictions are extremely accurate while the long term ones result in a sort of nonlinear filter able to extract the signal features concerned with the larger eddies and coherent structures present in the turbulent flow-field. [Copyright &y& Elsevier]

A multi-layer hydrostatic shallow-water model was developed in the present study. The layer-integrated hydrostatic nonlinear shallow-water was solved with θ time integration and the least-squares finite element method. Since the least-squares formulation was employed, the resulting system of equations was symmetric and positive–definite; therefore, it could be solved efficiently by the preconditioned conjugate gradient method. The model was first applied to simulate the von Karman vortex shedding. A well-organized von Karman vortex street was reproduced. The model was then applied to simulate the Kuroshio current-induced Green Island vortex street. A swirling recirculation was formed and followed by several pairs of alternating counter-rotating vortices. The size of the recirculation, as well as the temporal and spatial scale of the vortex shedding, were found to be consistent with ADCP-CDT measurements, X-band radar measurements, and analysis of the satellite images. It was also revealed that Green Island vortices were affected by the upstream Orchid Island vortices. [ABSTRACT FROM AUTHOR]

To accelerate the integration of fluctuating renewable energy technologies in the power systems, it is necessary to increase the flexibility of hydropower by operating turbines at off-design conditions. Unfortunately, this strategy causes deleterious flow phenomena such as von Kármán's vortices at the wake of the vanes and/or blades. When their shedding frequency lies in the vicinity of a structure's natural frequency, lock-in occurs and vibration amplitudes increase significantly. Moreover, if cavitation occurs at the centers of these vortices, the structure's dynamic response will be modified. In order to understand this interaction and to avoid its negative consequences, the vibration behavior of a NACA 0009 hydrofoil under a torsional lock-in condition was numerically simulated for cavitation-free and cavitating-flow conditions. The results showed that the presence of vortex cavitation modified the formation and growth process of shed von Kármán vortices in the near-wake region which, in turn, caused an increase of the work performed by the hydrofoil deformation on the surrounding flow and a sharp decrease of the maximum vibration amplitude under resonance conditions. [ABSTRACT FROM AUTHOR]