Effect Of Vortex Shedding Research Articles

Hydrodynamic characteristics of two tandem flexible cylinders undergoing flow-induced vibration

Flow-induced vibrations (FIV) of two tandem cylinders are the major concerns in many engineering fields. However, little attention is paid to the FIV mechanisms of two tandem flexible cylinders, especially for the hydrodynamic features. To investigate the FIV hydrodynamic characteristic of two tandem flexible cylinders, the fluid forces on the flexible cylinders were reconstructed by a finite element model using the response displacements acquired from model tests. Considering the coupling effect of multi-frequency vibrations, the lift coefficients, varying drag coefficients, cross-flow (CF) and in-line (IL) added mass coefficients were obtained utilizing the Forgetting Factor Least Squares (FF-LS) method. To investigate the influence of the spacing ratio T/D (where T is the center-to-center separation distance between the two cylinders and D is the cylinder diameter) on the FIV hydrodynamic features, five spacing ratios (T/D = 4.0, 6.0, 8.0, 10.0 and 16.0) were considered. The upstream cylinder and the single cylinder have CF hydrodynamic coefficients that share similar trends versus the reduced velocity, except for T/D = 4.0. The downstream cylinder may disturb the vortex shedding from the upstream cylinder, leading to the decrease in mean lift coefficients and mean varying drag coefficients on the upstream cylinder. Both the wake shielding effect and the vortex shedding effect have a significant influence on the hydrodynamic features of the downstream cylinder. Under the wake shielding effect, the mean lift coefficients and mean varying drag coefficients on the downstream cylinder are reduced, while the mean CF and IL added mass coefficients are increased. Owing to the vortex shedding effect, the mean lift coefficients and mean varying drag coefficients calculated using the local flow velocity are higher than those on the single cylinder, which increases the contribution of the adjacent modes to the vibrations.

On hydrodynamic behavior of fluid resonance in moonpool and its suppression by using various convex appendages

Fluid resonance in moonpool formed by two identical hulls undergoing heave oscillation is investigated by using a viscous fluid flow solver with RNG turbulent model based on OpenFOAM® package. By comparison of experimental and numerical results, it is confirmed the present numerical model can simulate the gap resonance problem in a high level accuracy. Numerical simulations suggest that the resonant amplitude in moonpool decreases dramatically when installing the convex appendages, which is the reason of significant variation of velocity flow field in the vicinity of moonpool. The single convex appendages at the bottom or near the free surface can generate smaller resonant amplitude than that at the middle of moonpool wall. The vortex bubbles from the convex appendages at the moonpool bottom create more energy dissipation than those for the convex appendages in the middle of moonpool and near the free surface. As for the multiple convex appendages, the variation of resonant amplitude with appendages types follows the suppressing characteristics of single convex appendages when heave amplitude is small. However, the additional appendages at the middle of moonpool wall shrink the region of vortex bubbles from the bottom appendages when the heave amplitude is large, leading to the increased resonant amplitude in moonpool. All of these phenomena indicate the complex effect of vortex shedding in the moonpool region on resonant behavior. Finally, the vertical force on each appendage in multiple types is always smaller than that on the appendage in single types, implying the multiple appendages types can reduce the fluid force on the appendage.

Super and sub-harmonic synchronization in generalized van der Pol oscillator

Effects of quasiperiodic beatings and sub- and super-harmonic synchronization reveal in plasma physics, optics, acoustics, neurophysiology, etc., but also very often in aero-elasticity of large slender engineering structures, e.g., bridge decks, towers, masts, high rise buildings, ropes, where these phenomena emerge in relation with vortex shedding effects. This applies mainly to quasiperiodic beatings that can be encountered especially in the lock-in regimes, when the vortex frequency becomes close to the structure eigenfrequency ω0 with a small positive or negative detuning. This phenomenon has been thoroughly investigated for the van der Pol system in the previous study by the authors of this paper. However, experimental testing in a wind tunnel showed also other phenomena that can occur in the system resonance zone due to excitations with a multiple or rational fraction frequency leading to sub- or super-harmonic synchronization. All these effects are very dangerous from the viewpoint of reliability and safety of respective systems and hence, a robust theoretical background for design of adequate countermeasures are worthwhile to be developed. In this subsequent study the original sub- and super-synchronization effects are identified and quantified including assessment of their dynamic stability.

Structured Porous Material Design for Passive Flow and Noise Control of Cylinders in Uniform Flow.

Cylindrical bodies in uniform flows can be coated with a porous medium as a passive flow and noise control method in an effort to reduce the acoustic effects of vortex shedding. To date, the employed open-cell porous materials typically possess a randomized internal structure. This paper presents the design and validation of a novel 3-D printed structured porous coated cylinder that has significant flexibility, in that the porosity and pores per inch of the porous coating can be modified independently and relatively easily. The performance of the structured porous coating design is compared against porous polyurethane and metal foam with the same coating dimensions and similar pores per inch and porosity via an experimental acoustic investigation, revealing strong similarity in the passive noise control performance of each material type. A numerical comparison illustrates the similarities of the wake structure of the 3-D printed porous coated cylinder to an equivalent Darcy–Forchheimer model simulation that represents a randomized internal porous structure. The performance similarities of these different porous material types indicate that a structured porous geometry can be used to understand the internal flow behavior of the porous medium responsible for reducing the cylinder vortex shedding tone that is otherwise extremely difficult or impossible with typical randomized porous structures. Moreover, significant potential exists for the porous structure to be further optimized or smartly tailored by architectural design for different control purposes, coating geometries and dimensions, and working conditions.

Numerical simulations of wind circumfluence around a Tensairity cylindrical beam and predictions of its response

Numerical simulations of wind circumfluence around Tensairity cylindrical beams and predictions of their response are presented in the paper. An appropriate computational fluid dynamics model (CFD) and a fluid-structure interaction (FSI) method are used to study circumfluent wind fields and wind-induced vibrations of the Tensairity cylindrical beams. Navier-Stokes equations for the incompressible fluid dynamic simulations and FSI analysis of the Tensairity cylindrical beam subjected to the wind flow are applied. Constant and simulated fluctuating wind fields were assigned to the investigated structure. A Spalart-Allmaras (SA) one-equation turbulence model that uses an eddy-viscosity variable with a nonlinear transport equation was applied in the CFD analysis. The finite element method is used to simulate the aeroelastic behavior of the Tensairity cylindrical beam subjected to constant and fluctuating wind effects. Aeroelastic response characterized by wind velocity fields and vortex-shedding phenomena around the cross-section of the inflatable structure are presented. Results obtained from the CFD and FSI analysis were compared. The vortex shedding effects may produce significant lateral (cross-wind) vibrations with nonlinear redistributions of forces and displacements as well as introduce additional deformations to the individual structural members of the Tensairity system. The wind-structure interaction analysis of the Tensairity cylindrical beam revealed, in particular, the sensitivity of the pneumatic structure to vortex induced vibrations with galloping effects.

Energy harvesting utilizing reciprocating flow-induced torsional vibration on a T-shaped cantilever beam

This paper proposes a T-shaped cantilever energy harvester powered by flow-induced torsional vibration. To collect and convert the mechanical (kinetic) energy into electric power, a pair of symmetrical acrylic cylindrical bluff bodies were installed onto the bottom surface of the T-shaped cantilever beam, one at each end; There is also one patch of Macro Fibre Composite (MFC) used as an energy collector and converter which was attached to the fixed end of the cantilever beam. This proposed setup of the energy harvester is able to generate sustainable electric power by harvesting natural mechanical power resulted from the torsional vibration of the beam due to fluid’s vortex shedding effects. The proposed energy harvester has the novelty in that our approach harvests fluid flow’s energy in a reciprocal fashion making full use of renewable energy incurred in areas surrounding the two bluff bodies. Both the theoretical and experimental analyses on the proposed energy harvesting structure were performed and demonstrated in this paper. The case in the test rig we studied on the proposed energy harvester was able to generate sustainable electric power of approximately 1.0 μW when flow speed was measured to be 0.33 m s−1 flowing through two bluff bodies each of 29.5 mm diameter. This work also looks into and discusses pros and cons of various scenarios in terms of structural geometric variations for system optimization of the proposed energy harvester.

Three-dimensional Oscillations of 21 Halo Coronal Mass Ejections Using Multi-spacecraft Data

Abstract We investigate the 3D structure of kinematic oscillations of full halo coronal mass ejections (FHCMEs) using multi-spacecraft coronagraph data from two non-parallel lines of sight. For this, we consider 21 FHCMEs which are simultaneously observed by the Solar and Heliospheric Observatory and the Solar TErrestrial RElations Observatory A or B, from 2010 June to 2012 August when the spacecraft were roughly in quadrature. Using sequences of running difference images, we estimate the instantaneous projected speeds of the FHCMEs at 24 different azimuthal angles in the planes of the sky of those coronagraphs. We find that all these FHCMEs have experienced kinematic oscillations characterized by quasi-periodic variations of the instantaneous projected radial velocity with periods ranging from 24 to 48 min. The oscillations detected in the analyzed events are found to show distinct azimuthal wave modes. Thirteen events (about 62%) are found to oscillate with the azimuthal wave number m = 1. The oscillating directions of the nodes of the m = 1 mode for these FHCMEs are consistent with those of their position angles (or the direction of eruption), with a mean difference of about 23°. The oscillation amplitude is found to correlate well with the projected radial speed of the CME. An estimation of Lorentz accelerations shows that they are dominant over other forces, implying that the magnetic force is responsible for the kinematic oscillations of CMEs. However, we cannot rule out other possibilities: a global layer of enhanced current around the CMEs or the nonlinear nature of its driver, for example the effect of vortex shedding.

Numerical Analysis on Effect of Jet Injection on Vortex Shedding for Flow Over a Circular Cylinder

Two-dimensional numerical investigations on the flow characteristics past a circular cylinder with a jet injection at the rear stagnation point are performed. Transient, incompressible, laminar, and isothermal flow governing equations are solved with finite volume method. Numerical simulations have been carried out at a Reynolds number of 150 with different injection ratios (IR) ranging from 0.5 to 7. Time evolutions of the coefficients of drag and lift, and streamline patterns are plotted. Three different flow pattern ranges are observed, namely wake dominant (IR $$\,=\,$$ 0–1.5), transition (IR $$\,=\,$$ 1.5–2.5) and jet dominant (IR > 2.5), and they are characterized by the combined effects of vortex shedding, undulation and jet dominant phenomena appearing in the flow downstream. It is also found that $$C_{\mathrm{d}}$$ decreases slightly with the injection ratio up to 1.5, after that it monotonically increases with the injection ratio. The similar incremental trend is observed in the Strouhal number variation with IR up to 1.5; then, it increases almost linearly till IR $$\,=\,$$ 4. When IR is greater than 4, there is a sudden drop in the Strouhal number value equal to zero and it remains constant after that for all the IR values considered in this study. The power spectral density of $$C_{\mathrm{l} }$$ indicates that the dominant frequency is present for the lower IR up to 4 and that no dominant frequency appears in the higher injection ratio range of 5–7 due to a complete suppression of the vortex shedding behind the cylinder by a dominant jet mechanism.

Aeroelastic analyses of bridges using a Pseudo-3D vortex method and velocity-based synthetic turbulence generation

The accurate representation of aerodynamic forces is essential for a safe, yet reasonable design of long-span bridges subjected to wind effects. In this paper, a novel extension of the Pseudo-three-dimensional Vortex Particle Method (Pseudo-3D VPM) is presented for Computational Fluid Dynamics (CFD) buffeting analysis of line-like structures. This extension entails an introduction of free-stream turbulent fluctuations, based on the velocity-based turbulence generation. The aerodynamic response of a long-span bridge is obtained by subjecting the 3D dynamic representation of the structure to correlated free-stream turbulence in two-dimensional (2D) fluid planes, which are positioned along the bridge deck. The span-wise correlation of the free-stream turbulence between the 2D fluid planes is established based on Taylor’s hypothesis of frozen turbulence. Moreover, the application of the laminar Pseudo-3D VPM is extended to a multimode flutter analysis. Finally, the structural response from the Pseudo-3D flutter and buffeting analyses is verified with the response, computed using the semi-analytical linear unsteady model in the time-domain. Meaningful merits of the turbulent Pseudo-3D VPM with respect to the linear unsteady model are the consideration of the 2D aerodynamic nonlinearity, nonlinear fluid memory, vortex shedding and local non-stationary turbulence effects in the aerodynamic forces. The good agreement of the responses for the two models in the 3D analyses demonstrates the applicability of the Pseudo-3D VPM for aeroelastic analyses of line-like structures under turbulent and laminar free-stream conditions.

Tianjin CTF Finance Centre: wind, form and structure

The Tianjin CTF Finance Centre is a 530m super-tall building nearing completion in the People's Republic of China. For a building of this height, wind forces and associated wind-induced motion in the upper levels can become dominant factors in the structural design of its foundations and lateral-stability system. This article describes how an initial aerodynamic shape-optimisation workshop allowed the design team to develop a finely tuned architectural form capable of minimising the detrimental effects of vortex shedding. This process, approx. 10 hours of wind tunnel time, was able to deliver key design information (e.g. peak dynamic overturning moments and wind-induced peak accelerations) in real time for a total of 17 aerodynamic variations of the tower form: a result which, previously, would only have been possible through an extensive and time-consuming campaign of wind tunnel tests. The way in which the wind loading was then refined, making use of simultaneous pressure integration and aeroelastic techniques, will also be described. Details about other wind engineering studies, aimed at investigating the pedestrian-level wind microclimate, the facade wind pressure, as well as the stack effect, will also be briefly presented.

Influence of height ratio on flow and heat transfer around trapezoidal geometry (a generic sharp-edged body) covering transition to periodic flow

Flow around an isolated generic sharp-edged object with varying height ratio (β = 0–1) i.e. height from the rear end of the object to the front end (β=H2/H1) has been investigated in cross-flow configuration covering steady and periodic regimes at Reynolds number (Re) from 1 to 150 using air as a working fluid. Flow separation is delayed with a decrease in β. Wake formed is the highest for β = 1 (square object) and progressively decreases with the decrease in β. The vortex shedding effect has been demonstrated on the heat transfer phenomena around the objects. For all the cases of height ratios, as Re increases the flow undergoes supercritical Hopf bifurcation to periodic state as steady-state condition loses its stability. Stuart-Landau theory has been used to determine the value of critical Re or the onset of vortex shedding for all the cases of height ratios. As β increases from 0 to 0.7, the value of critical Re increases. Influence of surface vorticity and surface pressure on the overall drag coefficient (CD) has been explored. Effect of β on the Strouhal number (St) has been investigated and the findings are in agreement with previous results. Finally, correlations relating Lr, CD, Nu‾ and St with Re and β have been developed.

Spectral Element Numerical Investigation of Flow between Three Cylinders in an Equilateral‐Triangular Arrangement with Different Spacing Distances

Two‐dimensional incompressible Navier‐Stokes equations are numerically solved using the high resolution spectral element method at Reynolds number 200. The flow between three cylinders in an equilateral‐triangular arrangement is investigated. The center‐to‐center spacing distance ratio between two circular cylinders is varied from 1.5 to 12. Present numerical results show that the flow patterns and force characteristics are the result of the combined effects of Reynolds number, spacing distance, configuration arrangement, and incident angle. For the small spacing distance ratio of 1.5, the well‐known biased flow phenomenon in the gap of downstream cylinders is found. And the biased flow is bistable in our study but not monostable. A small spacing distance means lower Strouhal number, drag, and root‐mean‐square lift coefficients. In the medium spacing distance ratio of 4.0, the suppressed effect of vortex shedding for the presence of the side‐by‐side downstream cylinders disappeared. Mean drag coefficients of downstream cylinders are basically identical to the value of flow past around a single circular cylinder. For the large spacing distance ratio of 8.0, the effects between three cylinders basically disappeared. The mean drag and lift coefficients, root‐mean‐square lift coefficients, and Strouhal number of three cylinders are essentially equivalent to those values of a single circular cylinder.

A CFD study of flow quantities and heat transfer by changing a vertical to diameter ratio and horizontal to diameter ratio in inline tube banks using URANS turbulence models

This paper reports the effect of changing the aspect ratio on the heat transfer and flow quantities over in-line tube banks. Two types of in-line arrangements were employed; square and non-square configurations. The models that were examined are a standard k-ε model, SST k-ω model, v2-f model, EB k-ε model and EB-RSM model. The closer results to the experimental data and LES were obtained by the EB k-ε and v2-f models. For the square pitch ratios, the solution has faced a gradual change from a strong asymmetric to asymmetric and then to a perfect symmetry. The strong asymmetric solution was found by the very narrow aspect ratio of 1.2. However, the behaviour of cases of 1.5 and 1.6 became less strong than that predicted in the case of 1.2. In the larger aspect ratio of 1.75, the flow behaviour is seen to be absolutely symmetric for all variables under consideration except Nusselt number. For the very large pitch ratio of 5, the flow has recorded maximum distributions for all parameters on the windward side of the central tube with a perfect symmetric solution around the angle of 180° while the vortex shedding frequency has recorded minimum value and the Strouhal number; therefore, has given the smallest value. However, for the non-square pitch ratio of constant transverse distance, the solution is still asymmetric for all parameters with merely one stagnation at the angle of 52° at the case of the 1.5×1.75 while by increasing the longitudinal distance to 2 and 5, the solution provided a comprehensive symmetry for all variables with two vortices are fully developed mirrored in shape on the leeward side of the central tube. On the contrary, for the non-square pitch ratio of constant longitudinal distance, the flow of the case of 1.75×1.5 provided two stagnation locations at around 52° and 308° with a very similar solution to the case square ratio of 1.75 for all variables whereas by increasing the transverse distance to 2 and 5, the solution recorded was not perfectly symmetric resulting in two different vortices and one stagnation position located at the leading edge of the cylinder provided by the case of 5×1.5. In terms of vortex shedding effect, the reduction in the Strouhal number at a constant transverse pitch is less steep than those at a constant longitudinal pitch.

Wind effects on a solar updraft power plant

A solar updraft power plant (SUPP) technology is a promising large-scale utilizing technology of renewable energy resource. Since the feasibility of the technology was demonstrated by the successful operation of the Manzanares pilot prototype, the plant performance has been widely studied. This paper carries out computational fluid dynamics (CFD) simulations of an SUPP, analyzes the characteristics of the mean and fluctuating wind pressures on the internal and external surfaces of solar updraft tower (SUT) and the upper and lower surfaces of solar collector roof, examines the effects of the SUT and baffle to the pressure on the roof's upper and lower surfaces, and discusses the effects of vortexes to the plant surface pressures and the potential effect of vortex shedding to the tower structural dynamics. It is hoped that this paper will guide further study and accurate design on this interesting power plant.

Wind-Induced Vibration Mitigation in Tall Buildings Using the Tuned Mass-Damper-Inerter

In this paper the classical linear tuned mass-damper (TMD) is coupled with an inerter, a two-terminal device resisting the relative acceleration of its terminals, in various tuned mass-damper-inerter (TMDI) topologies to suppress excessive wind-induced oscillations in tall buildings causing occupants’ discomfort. A parametric numerical study is undertaken involving a top-floor-TMD-equipped planar frame capturing accurately the in-plane dynamic behavior of a 74-storey benchmark building exposed to a quasi-stationary spatially-correlated wind-force field accounting for vortex shedding effects in the across-wind direction. It is found that the TMDI reduces the peak top floor acceleration more effectively than the TMD by considering smaller attached mass values, and TMDI topologies in which the inerter spans more stories in linking the attached mass to the host structure. Moreover, the inclusion of the inerter reduces dramatically the TMD stroke while it was verified that the magnitude of the developing inerter forces can be readily accommodated by the host structure. Pertinent illustrative examples are included showcasing that the TMDI meets code-prescribed serviceability design requirements for new tall buildings using significantly smaller attached mass compared to the TMD, and that inerter devices can be used to upgrade the performance of existing TMD-equipped tall buildings without changing the attached mass.

Prediction of Turbulent Flow Around a Square Cylinder With Rounded Corners

Predictions are reported of the two-dimensional turbulent flow around a square cylinder with rounded corners at high Reynolds numbers. The effects of rounded corners have proved difficult to predict with conventional turbulence closures, and hence, the adoption in this study of a two-equation closure that has been specifically adapted to account for the interactions between the organized mean-flow motions due to vortex shedding and the random motions due to turbulence. The computations were performed using openfoam and were validated against the data from flows past cylinders with sharp corners. For the case of rounded corners, only the modified turbulence closure succeeded in capturing the consequences of the delayed flow separation manifested mainly in the reduction of the magnitude of the lift and drag forces relative to the sharp-edged case. These and other results presented here argue in favor of the use of the computationally more efficient unsteady Reynolds-averaged Navier-Stokes approach to this important class of flows provided that the effects of vortex shedding are properly accounted for in the turbulence closure.

Unsteady Flow Structures and Pressure Pulsations in a Nuclear Reactor Coolant Pump With Spherical Casing

Severe vibrations induced by flow instabilities in the nuclear reactor coolant pump (RCP) are detrimental to the safe operation of the pump. Due to the particular spherical casing in the RCP, the internal flow structures are extremely ambiguity and complicated. The goal of the present work is to shed comprehensive light on the unsteady flow structures and its correlation with the pressure pulsations by using large eddy simulation (LES) method of the RCP. The vorticity distribution and the shedding vortex from the blade trailing edge are depicted in detail. Furthermore, the internal correlations between the flow unsteadiness and pressure pulsation are illustrated in some special regions of the RCP. Evidently, some main excitation components in the pressure spectra are excited by the shedding vortex. Besides, components at blade passing frequency (fBPF) are closely associated with rotor–stator interaction between the wake flow from the impeller outlet and unsteadiness vortexes shedding from the diffuser blade trailing edge. It is thought to be that the pressure pulsations of the RCP are closely associated with the corresponding vorticity distribution and the unsteady vortex shedding effect.

Identification of flow regimes around two staggered square cylinders by a numerical study

The flow over two square cylinders in staggered arrangement is simulated numerically at a fixed Reynolds number (\(Re =150\)) for different gap spacing between cylinders from 0.1 to 6 times a cylinder side to understand the flow structures. The non-inclined square cylinders are located on a line with a staggered angle of \(45^{\circ }\) to the oncoming velocity vector. All numerical simulations are carried out with a finite-volume code based on a collocated grid arrangement. The effects of vortex shedding on the various features of the flow field are numerically visualized using different flow contours such as \(\lambda _{2}\) criterion, vorticity, pressure and magnitudes of velocity to distinguish the distinctive flow patterns. By changing the gap spacing between cylinders, five different flow regimes are identified and classified as single body, periodic gap flow, aperiodic, modulated periodic and synchronized vortex shedding regimes. This study revealed that the observed multiple frequencies in global forces of the downstream cylinder in the modulated periodic regime are more properly associated with differences in vortex shedding frequencies of individual cylinders than individual shear layers reported in some previous works; particularly, both shear layers from the downstream cylinder often shed vortices at the same multiple frequencies. The maximum Strouhal number for the upstream cylinder is also identified at \({G}^{*}=1\) for aperiodic flow pattern. Furthermore, for most cases studied, the downstream cylinder experiences larger drag force than the upstream cylinder.

Optimum design of the tuned mass-damper-inerter for serviceability limit state performance in wind-excited tall buildings

Optimally designed tuned mass-damper-inerters (TMDIs) are considered to meet code-prescribed serviceability criteria in typical wind-excited tall buildings subject to vortex shedding effects in a performance-based design context. The TMDI, couples the classical tuned-mass-damper (TMD) with an inerter, a two-terminal device resisting the relative acceleration of its terminals, achieving mass-amplification and higher-modes-damping effects compared to the TMD. A benchmark 74-storey building is considered, where TMDI is added to the structural system assuming ideal linear inerter behavior. The wind action is defined through a non-diagonal power spectral density matrix supporting computationally efficient frequency domain structural analyses. The TMDI is optimally designed for stiffness, damping, and inerter constant parameters via a standard numerical optimization search, for a range of pre-specified attached TMDI mass values. It is shown that the TMDI achieves more lightweight construction in the design of new code-compliant tall buildings against wind.

Numerical Simulation of the Flow and Local Scour Process around Single and Complex Bridge Piers

The present work is focused on the flow and clear-water scour process around single and complex bridge piers using the computational fluid dynamics (CFD) approaches. In CFD, the use of large time steps may accelerate the simulation process but the effects of the unsteady flow structures may not be considered in the computations. In this case, the computational method is defined as a steady-state solution. In the present study, the capability and accuracy of the steady-state solution of the flow equations are investigated by employing the SSIIM code which is numerically stable for large time steps. For this purpose, several simulations were performed for different piers and bed configurations and the corresponding numerical results were compared with experimental ones obtained from referenced bibliography. Overall, the steady-state solution of the flow equations could predict fairly well the scour geometry at the upstream side and lateral sides of the bridge pier but not downstream side of the pier. Moreover, the local scour around a single pier was also predicted by performing an unsteady-state solution (where the vortex shedding effects are taken into account) by using the Flow-3D code. The major difference between the results from the two mentioned CFD codes was observed downstream of the pier such that, compared to the physical model, the scour depth was under-predicted by the steady-state calculations while it was over-predicted by the unsteady-state calculations.