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This study investigates the entropy generation analysis of natural convection flow within a diamond-shaped cavity filled with porous media. The research focuses on understanding the effects of a chamfered vertex and the introduction of one or two circular cold objects within the cavity. Using COMSOL Multiphysics software, the study examines various Rayleigh (Ra) and Darcy (Da) numbers to analyze the flow dynamics, heat transfer (HT), and entropy generation (Egen). Results indicate that the presence of cold objects significantly influences the flow patterns, enhances HT, and increases Egen due to fluid friction (FF). Higher Ra values lead to more vigorous convective currents, while lower Da values indicate a transition to conduction-dominated regimes. In addition, the heat transfer rate increases by 5 % by introducing a single cold cylinder inside the cavity for Da = 10−2 and Ra = 106. This enhancement rises to 16 % when two cold cylinders are introduced. The study provides valuable insights into optimizing cooling processes within diamond-shaped cavities by identifying key parameters that affect HT and irreversibility.

This paper is concerned with the strain gradient theory of porous thermoelastic solids. We study the deformation of isotropic chiral cylinders subjected to a temperature field that is linear in the axial coordinate. It is shown that the solution can be reduced to the study of two-dimensional problems. The results are used to investigate the deformation of a circular cylinder subjected to a uniform temperature variation. In contrast to the case of achiral materials, the thermal field in chiral cylinders produces torsional effects. [ABSTRACT FROM AUTHOR]

Parametric study is carried out on the transient cooling process of two circular cylinders in tandem arrangement for a specified period of time. Transient analysis of conjugate (conduction and convection) heat dissipation from two identicalcylinders is considered with various parameters. The two cylinders of same size and properties are bounded by an adiabatic flat wall from below and the cooling air is flowing normal to their axis (cross flow). The following parameters are investigated in the present study: Reynolds number, cylinders thermal properties, separation distance between the two cylindersand the cooling time. The laminar flow is considered with Reynolds number values from 50 to 500. The simulations are carried out for cooling thetwo cylinders made of carbon steels, plastics plexiglass and plywood. The local and average Nusselt number for both steady and transient cooling of the two cylinders are presented. The effects of the parameters are investigated and the results are presented to understand the process. It is found that increasing either the separation distance and/or the Reynolds number will increase the heat dissipation and reduce the cooling time. The results show that carbon steels cylinders need longer time of cooling compare with the plywood cylinders due to the difference in their thermal inertia.

Isothermal turbulent flow around circular cylinders arranged side-by-side was numerically simulated on a commercial finite-volumes platform, ANSYS® CFX, version 2020 R2. The turbulence was modeled by using k-ω shear stress transport (k-ω SST). Three different Reynolds numbers were computed, Red = 200, 1000, and 3000, which were based on the cylinder diameter, d, the free stream velocity, U∞, and the kinematic viscosity of the fluid, ν. Sided cylinders were spaced apart from each other, forming a p/d ratio equal to 2, which was kept constant throughout the computations regardless of changes in the Reynolds number. The drag coefficient, Cd, as well as its time traces, was evaluated along with the different wake topologies experienced by the cylinders (wide wake WW and narrow wake NW). The simulations were able to predict the bistable flow over the cylinders and the Cd changes associated with the wakes. Whenever a new wake topology was identified, the shape drag changed in accordance with the instantaneous pressure distribution. A laminar simulation was carried out for the lowest Reynolds number case, showing that the adopted turbulence model did not affect the dynamic response of the flow. The Red = 3000 case was compared to Afgan's outcomes, whose simulations were carried out in a 3-D mesh using LES (Large Eddy Simulation), showing great agreement with their results. [ABSTRACT FROM AUTHOR]

There are innumerable tests on small stocky circular cylinders with either internal passive encasement of the concrete with circular stirrups or spirals, or external passive encasement through fibre-reinforced polymer (FRP) wrapping or through the use of FRP tubes or steel tubes. These tests have shown that passive confinement can increase the strength but, in particular, can substantially increase the ductility of concrete cylinders. Because of these important benefits, the effect of passive confinement on the concrete stress/strain in a particular cylinder section is invariably derived from tests such that substantial member testing is required. In this paper, it is shown how the passive stress/strain of the concrete for a particular circular member can theoretically be determined directly from their partial-interaction shear-friction and partial-interaction bond-slip material properties for any reinforcement arrangement and geometry of the circular cylinder. This procedure provides tools for designing for the benefits of passive confinement directly without the need for member testing. [ABSTRACT FROM AUTHOR]

The steady flow of non‐Newtonian power‐law fluids across a periodic square array of infinitely long circular cylinders is studied numerically using an unstructured finite volume method. The local and global flow characteristics have extensively been explored by the systematic variations of the pertinent dimensionless parameters as follows: fluid volume fraction (ϕf =.70–.99), Reynolds number (Re = 1–40), and power‐law index (n =.4–1.8). Qualitatively, the dense and curved streamlines are seen with the increasing inertial forces and shear‐thinning behavior across all the fluid volume fractions. Further, the pressure coefficient over the surface of periodic cylinders is significantly influenced by the governing parameters and found to be maximum and minimum for the upstream and downstream cylinders, respectively. The individual and total drag coefficients have shown complex dependence on n, ϕf, and Re. For shear‐thinning fluids (n < 1), the pressure drag coefficient dominates over the friction drag coefficient, whereas an opposite response is seen for the shear‐thickening fluids (n > 1) except at Re = 40. Further, both individual and total drag coefficients are observed to increase and decrease in the ranges of ϕf of.70–.90 and.92–.99, respectively, with increasing n. The strong interactions between the periodic cylinders, at smaller ϕf, diminish with a corresponding increase in ϕf. In addition, simple predictive correlations for the pressure, friction, and total drag coefficients have been developed to gain further physical insights into the detailed flow kinematics. Finally, the present findings display a good agreement with the available literature. [ABSTRACT FROM AUTHOR]

Isothermal turbulent flow around circular cylinders arranged side-by-side was numerically simulated on a commercial finite-volumes platform, ANSYS® CFX, version 2020 R2. The turbulence was modeled by using k-ω shear stress transport (k-ω SST). Three different Reynolds numbers were computed, Red = 200, 1000, and 3000, which were based on the cylinder diameter, d, the free stream velocity, U∞, and the kinematic viscosity of the fluid, ν. Sided cylinders were spaced apart from each other, forming a p/d ratio equal to 2, which was kept constant throughout the computations regardless of changes in the Reynolds number. The drag coefficient, Cd, as well as its time traces, was evaluated along with the different wake topologies experienced by the cylinders (wide wake WW and narrow wake NW). The simulations were able to predict the bistable flow over the cylinders and the Cd changes associated with the wakes. Whenever a new wake topology was identified, the shape drag changed in accordance with the instantaneous pressure distribution. A laminar simulation was carried out for the lowest Reynolds number case, showing that the adopted turbulence model did not affect the dynamic response of the flow. The Red = 3000 case was compared to Afgan’s outcomes, whose simulations were carried out in a 3-D mesh using LES (Large Eddy Simulation), showing great agreement with their results.

This article deals with the influence of porous media on helical flows of generalized Oldroyd-B between two infinite coaxial circular cylinders.The fractional derivative is modeled for this problem and studied by using finite Hankel and Laplace transforms .The velocity fields are found by using the fundamentals of the series form in terms of Mittag-Leffler equation. The research focused on permeability parameters,fractional parameters(𝛽), relaxation (𝜆1), retardation (𝜆2), kinematic viscosity (v), magnetic parameter(M),and time (t), which affected the velocity fields u and w.The influences of the various flow parameters of the problem on these distributions are debated and proved graphically by figures . [ABSTRACT FROM AUTHOR]

Thunderstorms winds are localized and transient phenomena characterized by three-dimensional non-stationary velocity fields. While numerous studies investigated the wind loading on cantilevered structures under thunderstorm downburst winds, there is a lack of fundamental research on the behavior of simple circular cylinders subjected to downburst-like outflows. This paper investigates the pressure distribution and aerodynamic coefficients of two cylinders with different diameters immersed in three different types of wind: (1) isolated downburst (DB); (2) downburst embedded in an atmospheric boundary layer (ABL) wind (DBABL); and (3) steady ABL wind. The focus of this study is to provide a comparative analysis between aerodynamic coefficients (drag and lift) and surface pressures that result from these three different wind systems. The ABL winds caused a higher drag on the thinner cylinder than the two DB-like outflows. The lift coefficients during the primary vortex passage in the DB-like outflows were negative at the base of the cylinders and approached zero or to slightly positive values close to the cylinders' top. The location of the cylinders in DB-like outflows is the dominant factor for their aerodynamics. [ABSTRACT FROM AUTHOR]

For steady flow past two stationary circular cylinders that are aligned in tandem with their axes perpendicular to the flow direction, the wake pattern, vortex shedding frequency, and forces on the cylinders typically show an abrupt change as a function of the dimensionless center-to-center cylinder spacing over a range of critical spacing values. For R e ≲ 190 , the flow is expected to be laminar and two dimensional, and hence well behaved, yet prior experimental and computational results do not agree regarding the value of the critical spacing, ℓ c. Using flow visualization techniques in a flowing soap film system with R e = 99 (± 8) , we found the experimental critical spacing range to be 2. 9 ≲ ℓ c ≲ 4. 1 , lower than prior experimental results and consistent with published computational results. [ABSTRACT FROM AUTHOR]

Particle image velocimetry (PIV) of four cylinders with different cross sections were performed in a recirculating water channel at Reynolds numbers of 5000 and 10,000. The cylinders were split into two distinct categories; semicircular and convex-edged triangular (c-triangular) prisms which have a smooth diverging fore-face and a flat, backward facing step aft-face, and a trapezoid which has a flat fore face and a backward-facing step aft-face. The resulting streamwise and transverse velocity vectors (u and v, respectively) were analyzed to provide a qualitative comparison of the bluff body wakes to the circular cylinder, which is the standard upstream stationary body in wake-induced vibration (WIV) energy technology. The Reynolds stresses, turbulent kinetic energy (TKE), mean spanwise vorticity, and the energy in the fluctuating component of the wake were compared. The main findings are: (i) a convex fore-face and a backward-facing step aft face are more effective at converting the flow energy to temporal wake energy (+20%) compared to a circular cylinder, (ii) a trapezoid type shape is less effective at converting flow energy to temporal wake energy (-40%) compared to a circular cylinder, (iii) increasing Reynolds number reduces the efficiency of conversion of upstream flow energy to downstream transverse temporal energy. Utilizing stationary upstream bodies such as the semicircle and the c-triangle can result in concentrating more energy in the fluctuating components for the downstream transversely vibrating bluff body in a WIV system, and hence can realize in more efficient WIV technology. [ABSTRACT FROM AUTHOR]

The vortex-shedding phenomenon leads to a self-sustained vibration named Vortex-Induced Vibration (VIV), an important mass transfer enhancement method. This work studies the VIV effects of two circular cylinders inside a channel in a tandem arrangement on the mixing performance. A comprehensive study is conducted on different modes of cylinder vibrations, i.e., both cylinders vibrate, one cylinder vibrates, another cylinder is stationary, and both cylinders are stationary. The finite volume method is applied to solve the fluid flow equations, and the cylinders' vibration is modeled as a mass-spring-damping system. At low ranges of the reduced velocity, the vibration's amplitude of the cylinder is significant, and the mixing index reaches its highest values. For the case in which the distance between two cylinders is four times their diameter, the best mixing performance is related to two vibrating cylinders. In this mode, the mixing index increased up to 35% and 78% with respect to two stationary cylinders and a single stationary cylinder, respectively. Also, the investigation shows that increasing the distance between the cylinders improves the mixing process. For cylinders' distances of 4.5 and 5, the mixing index reaches 98% and up at the channel outlet. • Investigation on VIV of two circular cylinders in improving mass transfer. • Effect of vibration arrangement and distance between the cylinders on mixing characteristics. • In both cylinders vibrating mode the mixing index enhances 78% with respect to a single stationary cylinder. • For cylinders' distance of 5D in entrance length 17D, the mixing index value was obtained 95%. [ABSTRACT FROM AUTHOR]

This paper presents an exploratory analysis of the oscillation process of a set of two circular cylinders (D = 25 mm) mounted with a fixed pitch-to-diameter ratio P/ D = 1.26 and attached to a free-to-rotate circular table submitted to a turbulent crossflow in a wind tunnel. Measurements were performed with hot wire anemometers placed in the wake of the cylinders synchronized with a high-speed digital camera. Flow visualizations with static cylinders in a water channel were performed to investigate the wake formation around the cylinders. The analysis of the results was made through Fourier and wavelet transforms. The main objective is to address the observed phenomenon with its causing physical mechanism. Wind tunnel results showed that, depending on the imposed mean flow velocity, the set starts oscillating with a low steady amplitude. When the flow is disturbed, an increase in the oscillation amplitude is observed, remaining in this steady regime even after removing the disturbance. Although the interaction between the flow and cylinder set generates two stable states, the properties of the oscillation phenomena (frequency and amplitude) remained the same, pointing out an intrinsic property of the dynamical system. The vortex shedding is identified to be the primary mechanism responsible for initiating the small amplitude oscillation, while the flow passing through the gap between the cylinders is the cause of the high amplitude oscillation. The flow visualization corroborated the wake analysis described in the wind tunnel experiments. No evidence of coherence between the vortex shedding from the first cylinder and the oscillation process was identified. Considering the results in the present work, the configuration analyzed may work as a vortex-shedding suppressor. [ABSTRACT FROM AUTHOR]

The analytically obtained algebraic equation systems for the TM/TE-z polarized monochromatic waves scattering from eccentrically layered circular cylinders are ill-conditioned for numerical calculations. Therefore, such ill conditioned systems must be regularized for reliable numerical results. Here, the steps of the regularization of the ill conditioned system obtained for the scattered field from a circular metamaterial cylinder includes three parallel circular cylinders: a dielectric, an impedance and a perfect electric conductor is explained. In the regularization procedure used here each circular boundary brings block(s) correspond to its electromagnetic property and the regularization procedure is done according to this block(s). For this end a system that consists of perfect electric conductor (PEC), impedance, dielectric, and metamaterial cylinders is discussed and thus the steps of a regularization procedure for a general system that has all the type of boundaries in terms of electromagnetics will be explained here. As a result, if a new boundary is included to the system then it is sufficient to locate the blocks related to this boundary suitably. [ABSTRACT FROM AUTHOR]

This paper presents dependence of forces and flow structures on phase lags between vortex sheddings from three tandem cylinders. The flow around the three cylinders of an identical diameter D is numerically simulated at a Reynolds number Re  = 200 for spacing ratios L 1 * =  L 1 /D  = 3.5 - 5.25 and L 2 *  =  L 2 /D  = 3.6 - 5.5, where L 1 is the center-to-center spacing between the upstream and middle cylinders, and L 2 is that between the middle and downstream cylinders. The variations in L 1 * and L 2 * in these ranges correspond to the phase lags ϕ 1 (between the upstream and middle cylinders) and ϕ 2 (between the middle and downstream cylinders) both changing from inphase to antiphase. The flow around the cylinders is more sensitive to L 1 * than to L 2 * , while both ϕ 1 and ϕ 2 have more influences on cylinder 1 than on the other two. An inphase condition ( ϕ 1  =  ϕ 2  = inphase) corresponds to a high fluctuating lift and fluctuating shear-layer velocity but a small drag, Strouhal number, and time-mean shear-layer velocity for the upstream cylinder. On the other hand, an out-of-phase condition ( ϕ 1  = inphase/antiphase and ϕ 2  = antiphase/inphase) complements the opposite, a small fluctuating lift and fluctuating shear-layer velocity. [ABSTRACT FROM AUTHOR]

This paper presents the results of a wind tunnel test campaign conducted to investigate the aeroelastic and aerodynamic behaviour of a tapered circular cylinder in smooth flow conditions. The model under investigation is a single-mode aeroelastic one, whose taper ratio (in terms of diameter) is 8 %. Its global dynamic response was measured through the use of an internally-mounted piezo-electric accelerometer. The sensitivity of the vortex-induced response to different levels of structural damping was explored. The harmonic content of the wake was also measured through a hot-wire anemometer positioned downstream of the wind tunnel model at different heights: this allowed the detection of the portion of the model whose local resonance was accountable for the highest vortex-induced structural response. To further expand the findings of the wake measurements, four 'rings' of surface-mounted pressure sensors were installed on the wind tunnel model. The Reynolds number that was covered during the experiments ranged between 9. 3 × 1 0 3 and 3. 2 × 1 0 4 . The experimental investigations revealed that the tapering has a beneficial effect with respect to vortex-induced oscillations, reducing their magnitudes when compared against the ones of a parallel-sided circular cylinder. On the other hand, the lock-in region was found to be wider, exhibiting three distinct peak regions for the lowest level of structural damping. The combined results from the accelerometer, the hot-wire anemometer and the pressure measurements, and the application of tailored time–frequency analyses based on the continuous wavelet transform, revealed that the maximum dynamic response is linked to the local resonance between the fundamental frequency and the bottom portion of the structure. Furthermore, the magnitudes of the local mean aerodynamic drag coefficient and the local standard deviation of the (vortex-induced) lift coefficient were found to be considerably lower than those of a parallel-sided circular cylinder. [Display omitted] • VIV response of a highly tapered circular cylinder is experimentally investigated. • The VIV response curve exhibits three distinct peaks of a different nature. • Hot-wire anemometer measurements are used to localize VIV resonance regions. • Pressure measurements clarify the cellular vortex-shedding ruling the VIV response. • The aerodynamic coefficients are reduced than those of parallel-side cylinders. [ABSTRACT FROM AUTHOR]

The paper presents a collection of full-scale data selected from literature concerning measurements of cross-wind vibrations of chimneys. They belong to the original set of data, from which current codified methodologies - the Spectral Method by Vickery&Basu (1983) and the Effective Correlation Length Method by Ruscheweyh (1986) - were developed. The full-scale samples are critically reviewed; uncertain estimations and observations by eye are discarded. The application of the codified methodologies to the selection of full-scale chimneys reveals several inconsistencies in the prediction of cross-wind oscillations. The paper presents a novel Spectral Method, whose predictions reproduce very well the oscillations measured in full-scale. The method is developed through wind tunnel tests in forced-vibrations. The key is the modification of the aeroelastic damping model in the well-known Vickery Spectral Method. [ABSTRACT FROM AUTHOR]

The interaction of regular waves with a weakly submerged horizontal circular cylinder at Keulegan-Carpenter KC numbers up to 2.5 is studied by means of numerical simulations, solving the two-phase flow Navier-Stokes equations with the Finite Volume method and the Volume of Fluid interface capturing method. Experimental data from laboratory tests conducted in the past by one of the authors are used as reference data. The study is focused on the surface wave transformation, on the flow field in the near region and on the loads on the cylinder. The interest is driven on the spectral content of the transmitted waves at higher order frequencies and on the non-linear features of the wave reflected by the cylinder. The flow field in the near-body region is analyzed in terms of vortex onset, development and detachment, and correlating pressure pulses with the vorticity field at the cylinder surface. Inviscid flow simulations are carried out too, to evince the origin of higher order terms either from the free surface or from the viscous terms in the momentum equations. The steady streaming around the cylinder is analyzed, including its variability along the cylinder surface and its relationship with the vortex cores generated at the body surface. [ABSTRACT FROM AUTHOR]

Experiments have been carried out with circular cylinders fitted with a suppressor of vortex-induced vibrations called the Ventilated Trousers (VT). Tests were performed at laboratory scale in a free-surface water channel with fixed and free-to-respond models in one degree of freedom. The oscillating tests were performed with elastically mounted cylinders with low mass and damping ( m * ζ < 0.009 ). Reynolds number varied from 5000 to 25000 and reduced velocity varied between 2 and 15. Tests with fixed models showed that the VT increased the mean drag and practically eliminated the fluctuating lift force when compared to a bare fixed cylinder. Free-response tests showed that the VT was able to reduce 60% of the peak amplitude of vibration, thus reducing the maximum drag compared with that of a bare oscillating cylinder. Three hypotheses are proposed to explain the physical mechanism underlying the suppression by the VT: local disruption of vortex shedding; three-dimensional disruption of the near wake; and the increase of hydrodynamic damping. [ABSTRACT FROM AUTHOR]

The control of flow in the wake of a circular cylinder by an attached permeable plate having various porosity ratios was analyzed experimentally using both particle image velocimetry (PIV) and dye visualization techniques. The force measurements were also done in order to interpret the effect of control method on drag coefficient. The diameter of the cylinder and length to diameter ratio of the plate were kept constant as D = 50 mm and L/D = 1.0, respectively. The porosity ratio, β, which can be defined as the ratio of open surface area to the whole body surface area, was taken as β = 0.4, 0.5, 0.6, 0.7, and 0.8 (permeable plates). The study was performed considering deep water flow conditions with a constant Reynolds number of ReD = 5000 based on the cylinder diameter. Each permeable plate was attached on the separation point and the results were compared with the results of cylinder without permeable plate (plain cylinder) in order to understand the control effect. Both qualitative and quantitative results revealed that the permeable plates of 0.4 ≤ β ≤ 0.6 are effective on controlling the unsteady flow structure downstream of the cylinder, i.e., the vortex formation length was increased, turbulent statistics was reduced and vortex shedding frequency was diminished when the permeable plate attached normal to the cylinder surface from the lower separation point. However, the drag force acting on the cylinder was found to be increased due to the increased cross-sectional area. [ABSTRACT FROM AUTHOR]

The aim of this work is to study laminar mixed convection heat transfer characteristics within an obstructed enclosure by using the Lattice Boltzmann method. Flow is driven by a top cold lid while other walls are stationary and adiabatic. Hot cylinders are located at different places inside the cavity to explore the best arrangement. Comparison of streamlines, isotherms, average Nusselt number are presented to evaluate the influence of Richardson number and location of cylinders on flow field and heat transfer. Results indicate that heat transfer decreases with a rise of Richardson number for all considered arrays of cylinders. Among them, horizontally-located cylinders at the top of the cavity have the greatest heat transfer at all Richardson numbers. Horizontally located cylinders at the bottom of the cavity have the lowest heat transfer at Richardson numbers of 0.1 and 1 while the lowest heat transfer rate belongs to cross diagonal located cylinders at a Richardson number of 10. [ABSTRACT FROM AUTHOR]

Fluid-dynamic loads have a great influence on the design of many Civil Engineering structures. In particular, circular sections are widely used in constructions, yet when it comes to aero- or hydro-dynamics simple geometry brings a complex behavior, as the features of flow separation strongly depend on Reynolds number. This has triggered a remarkable research effort towards the understanding of the aerodynamic behavior of circular cylinders. Indeed, circular cylinders used in Engineering applications are seldom perfect ones. In many cases, it has been observed that imperfections affect aerodynamics to a large extent. For this reason, a considerable effort has also been devoted to the understanding of how aerodynamics is modified by imperfections. This paper contains a review of existing literature on experimental results of interest for Civil Engineering applications on the aerodynamics of cylinders, whose geometry deviates from that of a perfect circular cylinder. Such deviations are classified into cylinder and flow irregularities, and the former are further subdivided into surface, section and spanwise irregularities. The need for further research is pointed out at the end of the paper. [ABSTRACT FROM AUTHOR]

Flow field characteristics in the neighbourhood of a finite height circular cylinder mounted on a horizontal plate have been investigated numerically. Three-dimensional simulations are carried out for low Reynolds number (Re) incompressible flow using commercial software ANSYS Fluent 14.0. Topological characteristics of the flow have been investigated near the cylinder of aspect ratio (AR) ranging from 0.5 to 3.0 with Re varied in the range from 40 to 300. Time-averaged streamline plots are presented in various planes for different values of AR and Re to understand the flow field characteristics. For a developing flow impinging on the cylinder, flow separation in upstream of cylinder close to the cylinder-bottom wall junction leads to horseshoe vortex formation. Various topological characteristics like saddle, node have been identified in upstream and downstream of the cylinder. Positions of saddles are shown to depend on the values of AR and Re. Development of recirculation region and formations of vortex bubble have been studied in form of their projections on different planes. The variation of mean drag coefficient on the cylinder with Re for different values of AR has also been presented. [ABSTRACT FROM AUTHOR]

Ultimate limit state and fatigue analyses of slender structures in vortex-induced vibrations require knowledge of aerodynamic damping in the lock-in range. The aerodynamic damping depends primarily on the shape of the cross section. The paper provides an experimental database of aerodynamic damping functions for different shapes, with a focus on sharp-edged cross sections. The data are discussed with respect to existing results available for circular cross sections. The aerodynamic damping is measured directly through wind tunnel tests in forced vibrations. Wind tunnel tests in free vibrations are used to extend the functions in the range of large oscillations and to validate the model. This concept is implemented in a well-founded calculation method for vortex induced vibrations for the design of slender structures. This is suitable for code applications and is in line with the procedure described in the latest generation of Eurocode. The novelty with respect to previous models like the Vickery&Basu model consists in an aerodynamic damping parameter with positive curvature. This can be easily controlled for varying cross sections by changing the value of the function exponent. • Aerodynamic damping functions for vortex induced vibrations • Calculation methods for vortex induced vibrations • Vortex induced vibrations for sharped edge cross sections • Interpretation of aeroelastic behaviour using forced vibration wind tunnel tests. [ABSTRACT FROM AUTHOR]

A subsidence of circular cylinders between rigid stamps at creep conditions is studied. There are three different material models. Appearance of barrel shape form is allowed (this decision is realized on the basis of package LS-DYNA). Calculations of all principal parameters were carried out at two loading programs: at constant speed of the cylinders' bases coming together and at constant compressing force. Calculations have shown that the energy, spent on subsidence of the cylinder during the first loading variant isless, than in the second variant (this difference in certain processes is equal to 8-10%).

We investigate the drag load on low-aspect ratio circular cylinders, submerged as in infinite fluid and subjected to steady current. A series of experiments are carried out in a circulating water tunnel with three different types of models; open and closed cylinders, and open with a splitter plate inside the middle of the cylinders. The length-to-draft ratio of the models, L / D , varies from 0.15 to 0.6. The Reynolds number, based on the cylinder diameter, varies from 40 000 to 105 000. The experiments show small Reynolds number dependency. The drag coefficient, C D , varies substantially for the open cylinder case; being around 2 for the lowest aspect ratios L / D ≤ 0. 2 , while 0.65-0.8 for L / D > 0. 25. There is an abrupt change of flow pattern for L / D = 0. 25 : for L / D ≤ 0. 2 the flow which is separated from the front half of the cylinder goes through the cylinder, producing a wide von Karman type vortex street, while for L / D ≥ 0. 25 the flow does not go through the models and, as a consequence, produces a significantly more narrow wake. The wide wake regime is suppressed when the splitter plate is added, with drag coefficients C D = 0. 6 − 0. 8. The drag coefficients for the closed cylinders are lower than the ones with splitter plate, and also consistent with published data on low-aspect ratio closed cylinders. A rational drag load model is proposed for the high-drag regime, with reasonable results. Tests where the cylinder with splitter plate is sectioned into a front and a rear half are presented, revealing a very small contribution of the drag from the rear half. This is discussed in view of existing studies on two-dimensional flat plates in tandem. [ABSTRACT FROM AUTHOR]

In this study, we solved numerically the double-diffusive natural convection over circular cylinders in a non-Darcy porous enclosure filled with nanofluids using a simple algorithm in a finite volume method. Here, the inner circular cylinders are maintained at a hot temperature T h , and concentration C h . The enclosure vertical side walls are maintained at a cool temperature T c , and concentration C c , and the horizontal walls are assumed to be adiabatic. The nanofluids on the outer enclosure walls and inner cylinders are passively controlled. We investigated the effects of the circular cylinders locations and sizes on the heat and mass transfer and fluid flow. The effects of Rayleigh number, Darcy parameter, Soret number with modified Dufour number and nanoparticles parameters in heat and mass transfer and fluid flow have been studied with graphical illustrations. It is found that, the size and formation of cells inside the enclosure strongly depend on the Rayleigh number with Darcy parameter, and sizes and locations of the inner circular cylinders. The current numerical results are well validated with a reasonable agreement. [ABSTRACT FROM AUTHOR]

Chiral effects cannot be described by means of the classical theories of continua. In the context of the strain gradient theory of porous elastic solids we study the deformation of a chiral cylinder subjected to torsion, extension and bending by terminal couples. This work is motivated by recent interest in using the chiral continuum as a model for some auxetic materials, bones and carbon nanotubes. The problem is reduced to the study of some two-dimensional problems. We show that the torsion of a chiral cylinder is accompanied by extension, bending, and a variation of the volume fraction field. The solution is used to investigate the deformation of a circular cylinder. [ABSTRACT FROM AUTHOR]

A density-based solver for turbomachinery application is developed based on the central-upwind scheme of Kurganov using the open source CFD-library OpenFOAM. Preconditioning of Weiss and Smith is utilised to extend the applicability down to the incompressibility limit. Implicit residual averaging, bulk viscosity damping and local time stepping are employed to speed up the simulations. A low-storage four-stage Runge-Kutta scheme and dual time-stepping are used for time integration. The presented solver is validated using measurement data from three well-known reference cases. The inviscid performance is investigated using the circular bump test cases at incompressible, subsonic, transonic and supersonic conditions. The laminar flow around a circular cylinder is analysed and compared to analytical and experimental data. Finally, a low speed centrifugal compressor is simulated. All three cases show a very good agreement with the reference data. [ABSTRACT FROM AUTHOR]

The present numerical study aims at the control of vortex shedding and drag reduction by shaping the rear geometry of a circular cylinder. The ratio of the semi-major/minor axis dimension (A) of the rear half to the radius of the circular part (R) is varied over a range of values between 0.0 and 4.0. A two-dimensional flow solver has been developed using body-fitting coordinate transformation with Cartesian velocity components as dependent variables and solved using a modified MAC algorithm. The flow solver offers a fast and accurate procedure for modelling viscous incompressible flows in complex geometries. The effect of elongation on the wake characteristics and hydrodynamic coefficients has been investigated for different values of Reynolds number (Re) ranging from 40 to 200. The predicted results indicate that vortex suppression occurs primarily due to reduction in the amplitude of fluctuation than by reduction in the vortex shedding frequency. The critical value of Re for the onset of vortex shedding has been correlated with elongation ratio ER, based on the numerical predictions. [ABSTRACT FROM AUTHOR]

Shape modification has been one of the effective ways of manipulating the flow past bluff bodies. Aiming at exploration of the flow control mechanisms of shape modified circular cylinders, a series of numerical simulations are conducted at the Reynolds number of 5000. The modifications adopted in the current paper could be divided into two categories, the 2-dimensional cross-sectional modifications (polygonal and ridged) and 3-dimensional span-wise modifications (linear wavy, sinusoidal wavy and O-ringed). By exploiting the numerical data obtained from the Large Eddy Simulations, several aspects, including the wake flow properties, the aerodynamic forces, the flow instabilities and span-wise correlations are compared in detail. The two wavy cylinders are found to modify the flow wake significantly, leading to considerable reduction in aerodynamic forces. The polygonal and ridged cylinders, however, are of no such effect in aerodynamic force mitigation. The O-rings only have slight effect on the flow wake and the forces. As for the flow instabilities, the modifications adopted in this paper barely affects the Kármán vortex shedding frequency. The shear layer frequency, however, differs from case to case. Particularly, in the cases of the two wavy cylinders, disparity exists in the shear layer frequency at the node and saddle. This is explained by the boundary layer properties at separation. While recognizing the insufficiency in the span-wise length of the cylinders, the span-wise correlations of the aerodynamic forces are inspected. It is found that the lift forces of the 3-dimensional cylinders are generally less correlated than that of the 2-dimensional ones. [ABSTRACT FROM AUTHOR]

This study proposed a transient 2-D hydrodynamic model adopting streamline upwind/Petrov-Galerkin (SU/PG) scheme for the analysis of discontinuous wave propagations by the sudden collapse of circular cylinder as well as by the dam break. The computation of sudden collapse in the circular cylinder problem identified both the outward-propagating circular shock waves and inward-propagating circular rarefaction waves. It was also confirmed that the advancing front and the depressive wave preserve the cylindrical symmetry, and the bore wave without oscillations was computed. The simulation results of the dam break shows that the bore and depressive waves which are propagating downstream and upstream, respectively are effectively developed and the shock front is sharply captured. The SU/PG scheme needs no tuning of adjustable parameters such as the artificial viscosity coefficient to be a viable option for accurate prediction of the flow characteristics in a discontinuous free surface case. [ABSTRACT FROM AUTHOR]

The combined effects of different rotation types and the Reynolds number on the flow past two rotating circular cylinders about their axes in different arrangement (Side-by-side and tandem) were considered at a range of 520 ≤ Re ≤ 1570 and 0 ≤ ω ≤ 4 (ω is the rotational speed) at one gap spacing of L/D = 2 for a side-by-side arrangement, ω = 0, 2000 ≤ Re ≤ 21000 and L/D = 2 and 4/3 for tandem arrangement (L and D are the distance between the centers of two cylinders and the cylinder diameter, respectively). The results show that the variation of both rotation speed and Reynolds number have an important role in changing the pattern of vortex shedding. As the rotational speed further increases, the separation phenomenon in the boundary layers disappears at the attachment rotational speed. Regardless of Reynolds number, as ω increases, the lift decreases for up and down cylinders while the drag decreases for up cylinder and increases for down cylinder. Quantitative information is highlighted about the flow variables such as the pressure coefficient the Stanton number, the skin friction factor and wall viscous coefficient of the cylinders. [ABSTRACT FROM AUTHOR]

Marine growth is a large technical, economic and environmental problem for almost all activities at sea. Circular cylinders being widely used in different types of offshore structures, this study focuses on the effects of different types of marine growth on cylinders׳ wake structure for low Re steady flows (2.16×10 3 < Re <1.94×10 4 ). Qualitative results from wake visualisations and simple drag force measurements confirmed that soft and hard roughnesses have completely different effects on the cylinder hydrodynamics for the transitional subcritical regime, as soft fouling act as a passive flow separation control. This study highlights the changes on the cylinder hydrodynamics induced by a developing fouling community, going from small hard roughnesses to fully developed soft fouling. [ABSTRACT FROM AUTHOR]

Wake-Induced Vibration (WIV) has been considered as a potential candidate to capture hydrokinetic energy. This paper reports the results of an experimental investigation of the WIV of a circular cylinder, positioned in the wake of an upstream circular cylinder. Investigations were carried out to determine the effects of the arrangement of the cylinders, with respect to each other, and the Reynolds number on the amount of energy, which can be harnessed from the shed-vortices. The upstream cylinder was kept stationary during the experiment, while the downstream cylinder was mounted on a virtual elastic base. The virtual elastic mechanism consists of a motor and a controller, a belt−pulley transmission system and a carriage. In comparison with the more traditional mechanical impedance mechanisms, comprising of a real spring and damper system, the virtual mechanism, utilized in this work, provided greater flexibility and robustness. The Reynolds number based on the diameter of the upstream cylinder was varied between 2000 and 15000. The tests revealed that the power coefficient of WIV power is a function of the Reynolds number and the phase shift between the fluidic force and displacement of the downstream cylinder. The results indicated that the amount of WIV energy, that can be captured, increases in a staggered arrangement, in comparison with an aligned arrangement. [ABSTRACT FROM AUTHOR]

This experimental study examines the effects of placing a control cylinder of small diameter and height in the upstream region of a main cylinder at a gap of 0.75 D in tandem arrangement on laminar junction flow at Re $$_D$$ = 1.3 $$\times $$ 10 $$^3$$ . The study is performed using 2D particle image velocimetry (PIV). The experiment clearly visualizes the changes in flow pattern with this arrangement and gives insight into the new flow pattern. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]