Identical Cylinders Research Articles

Numerical investigation on flow-induced vibrations of two staggered square cylinders using GPU-IB-LBM

A numerical investigation was conducted using a graphical processing unit for a multicylinder system. The aim was to study the flow dynamics around a pair of identical square cylinders arranged in staggered configurations, with a low Reynolds number of 100. The staggered angle of the downstream cylinder was systematically varied as 0° – 45°, while distance between the cylinder centers ranged as 1.5D – 5.0D. Both cylinders maintained a consistent mass ratio of 10.0, fixed frequency ratio of 1.0, and fixed natural frequency was chosen to achieve optimal oscillation amplitude. The results of this study highlighted the notable influence of proximity gaps on oscillation response. Moreover, introduction of staggered angles further amplified cylinder oscillation. In scenario involving two square cylinders, an intriguing fluid-induced vibration phenomenon occurred when a proximity gap of 1.5D was combined with a downstream rotational angle of 45°, resulted highest level of oscillation response. The research demonstrated that for smaller proximity gaps and the incorporation of angles, the oscillation positions of cylinders deviated from center. With increase in proximity gaps, oscillation positions converged back toward center. Notably, with widest proximity spacing of 5.0D, oscillation pattern of the upstream cylinder closely resembled that of an individual square cylinder.

Experimental investigation of the Eckert-Weise effect (aerodynamic cooling) of pair side-by-side circular cylinders in a compressible cross-flow

The rear surface of a thermally insulated circular cylinder placed in a subsonic high-velocity cross-flow is significantly cooled, this phenomenon is known as aerodynamic cooling or the Eckert–Weise effect. This effect is associated with the redistribution of the stagnation temperature (energy separation) in the unsteady vortex wake. Experiments show that the effect is maximal at Mach numbers of the free-stream flow of 0.5–0.7, resulting in negative values of the temperature recovery factor (the temperature of the cylinder rear surface becomes lower than the static temperature of the free-stream flow). In this case, the cooling of the rear surface can reach tens of degrees. This effect can be utilized as the basis for a novel energy separation device, as it enables heat transfer between flows with the same stagnation temperatures. As shown in a numerical study (Aleksyuk, 2021), the effect is highly sensitive to the flow interference behind side-by-side cylinders, this is especially important for its practical application. In this study, the aerodynamic cooling of a pair identical circular cylinders in side-by-side arrangement, is experimentally investigated within the Mach and Reynolds number ranges of M = 0.34–0.58 and ReD = 1.6∙105–3.1∙105. The cylinder spacing considered in this study (P/D = 1.1; 1.5; 2.0; 3.0; and 4.0, where P is the center-to-center cylinder spacing and D is the diameter) covered the key regimes of vortex interference, that is, single, bistable, and coupled vortex streets. Also, investigations were conducted for a single circular cylinder with the same diameter within the Mach and Reynolds number ranges of M = 0.34–0.68 and ReD = 1.6∙105–3.4∙105. The channel blockage ratio was found to be 8% for a single cylinder and 16% for a pair of cylinders. Consequently, this study focuses on confined flow or flow past a confined cylinder with a uniform profile of oncoming flow velocity. It is shown that the Eckert-Weise effect for the pair of cylinders can either increase or decrease depending on the interference regimes and is sensitive to the blockage ratio value.

Numerical investigation of power-law flow past two side-by-side identical circular cylinders

The non-Newtonian flow past multiple cylinders is widely encountered in engineering applications, such as slurry transport, petroleum drilling, and heat transmission systems using hot kerosene. However, the wake characteristics of non-Newtonian flow past multiple cylinders are far from well understood. This paper reports the numerical results of power-law flow past two side-by-side identical circular cylinders with a various gap ratio (G/D = 1.1–6.0) and a power-law index (n = 0.8–1.5) at a fixed Reynolds number (Re = 100) based on the incoming uniform flow velocity. Six wake patterns are identified, including the single bluff-body regime, deflected regime, in-phase regime, anti-phase regime, and two subclasses of flip-flopping regime (FF1 and FF2 regimes). The hydrodynamic coefficients of two cylinders are sensitive to both the gap ratio and the power-law index. The wake structure evolution is closely related to the wake patterns, and six modes of wake evolution are accordingly observed. Since the apparent viscosity of power-law fluid changes with the shear rate, the distribution of local Reynolds number (ReL) around the cylinder surface varies with the wake pattern. As it goes outward along the normal direction from the cylinder surface, the ReL shows a trend of increasing and then decreasing when n < 1, while the opposite trend is observed when n > 1.

Exploring kinematic stability of vortex structures: A topological approach to fluid flow around staggered square cylinders

In this study, a detailed fluid dynamics analysis is conducted around two identical square cylinders in a staggered configuration at a Reynolds number (Re) of 40, using a stabilized finite-element method to investigate the kinematic stability of vortex structures. By varying the horizontal spacing (S/D) between 2 and 30 and examining transverse gaps (T/D) of 0.25, 0.8, and 1.25, the research uncovers significant flow behavior variations from the tandem configuration, highlighting complex fluid-structure interactions. The presence of “separation bubbles” at lower S/D values across all T/D ratios indicates the dynamic impact of the upstream cylinder's proximity on the flow field, particularly on the stagnation points of the downstream cylinder. Through a comprehensive topological analysis, the study identifies various flow regimes and topological bifurcations, revealing transitions between stable states that maintain the number of critical points constant, and the kinematic stability of these vortical structures is established by the critical point theory. The effect of cylinder configurations and diverse flow structures on fluid loading is also analyzed by examining surface pressure coefficients. The asymmetry present in the cylinder configuration is manifested through the asymmetric values of lift coefficients.

Flow-induced vibration of two tandem square cylinders at low Reynolds number: transitions among vortex-induced vibration, biased oscillation and galloping

The flow-induced vibrations (FIVs) of two identical tandem square cylinders with mass ratio m* = 3.5 at Reynolds number Re = 150 are investigated through two-dimensional direct numerical simulation (DNS) and linear stability analysis over a parameter range of spacing ratio 1.5 ≤ L* ≤ 5 and reduced velocity 3 ≤ Ur ≤ 34. Three kinds of FIV responses, namely vortex-induced vibration (VIV), biased oscillation (BO) and galloping (GA), are identified. The FIVs are then further classified into the branches of initial VIV (IV), resonant VIV (RV and RV′), flutter-induced VIV (FV), desynchronized VIV (DV), VIV developing from GA (GV), transitional state between VIV and GA (TR), BO and GA based on the characteristics of the vibration responses. The transitions among different FIV branches are examined by combining the DNS with linear stability analysis, where the transition boundaries among the VIV, BO and GA branches over the concerned parameters are identified on the branch maps. The transition from IV to RV or RV′ is found to be related to the unstable wake mode, while the FV, transiting from RV or RV′, is induced by the unstable structural factor in the wake-structure mode. The structural instability is considered as the physical origin of GA, whereas the mode competition between unstable wake and structure leads to DV, GV and TR, and thus delays the appearance of GA. The transition from DV to BO with biased equilibrium position, accompanied by the even-order harmonic frequencies, is essentially induced by the symmetry breaking bifurcation.

Characterizing vibrations and associated wake structures of tandem square cylinders at different angles of incidence

Finite element computations were conducted to investigate the transverse vibrations of three identical tandem square cylinders and the associated wake patterns at a Reynolds number Re = 150. The reduced velocities ranged from U*=3 to 20, and the angles of incidence were set at α=0°, 22.5°, and 45°. The streamwise gaps for these three α were Lx=5H, 3.8H, and 3.5H, respectively, where H represents the projected dimension of the cylinder normal to the freestream. The mass ratio of the cylinders was fixed at m*=2, and damping was neglected to allow the cylinders to attain maximum amplitudes. In the presence of primary vortices being shed from all three cylinders, the upstream cylinder at α=22.5° and 45° exhibits three distinct vibration regimes: initial excitation and upper and lower response regions. On the other hand, due to interaction with the upstream vortices, the two downstream cylinders display four response regions. In the case of α=0°, the dynamic response of the upstream cylinder appears in only two regimes, but with a higher peak amplitude compared to α=22.5° and 45°. Vibration and shedding frequencies closely synchronize with the natural frequency of the spring-mass system in the second regime, leading to high amplitude oscillations for the most upstream cylinder with α=22.5° and 45°. The third response regime for the two downstream cylinders is associated with the lock-in phenomenon. In α=0° and 22.5° configurations, the shedding mode is 2S in all response regimes, while at α=45°, the shedding mode shifts to P + S during the second regime. Up to the second regime, lift and vortex forces are in-phase with the cylinder's oscillation for α=0° and 22.5°, but they go out of phase beyond that. In the case of α=45°, although lift remains in-phase with the displacement in the second regime, the vortex force is found to be out of phase. This study is expected to enhance the understanding of fluid–structure interaction phenomena involved in multiple structures and can aid in the design of stable structures in civil engineering, offshore engineering, and development of energy harvesting devices.

Nonlinear buckling of steel cone-segmented cylinders under external pressure: numerical and experimental evaluations

ABSTRACT The nonlinear buckling of cone-segmented cylinders under external pressure has been investigated. The cylinders include four nominally identical cones and their slant angles ranged from 0°–20° in every 1° increments. Note that the cylinder with a 0° slant angle forms a circular cylinder that is used for comparisons. Two nominally identical cone-segmented and circular cylinders have been fabricated, manufactured, measured, and tested. The numerical simulations for these cylinders are in good agreement with their experimental counterparts. Both linear and nonlinear buckling behaviours of the cylinders have also been evaluated, and the optimal slant angle can then be identified to be 6°–8°. These optimal imperfect cylinders yield buckling loads 1.7–2.8 times greater than those of an imperfect equivalent circular cylinder. Our results reveal a new finding that the average buckling load of the cone-segmented cylinders is approximately 2.3 times that of the equivalent circular cylinders.

Enhancing hydrodynamic drag and lift reduction around two staggered obstacles via control plates

This study analyzes the enhancement of hydrodynamic forces reduction for flow around two identical square cylinders arranged in a staggered manner utilizing the control plates. Effects of attached flat plates on flow structures and fluid forces acting on cylinders are examined by considering plates length (l) = 0.1–10 times cylinder’s size. The gap distance between cylinders (g) is fixed at 2.5 times cylinders' size with a fixed Reynolds number of 200. Four different flow patterns revealed in this study: synchronized flow pattern for l = 0.1 to 0.6, quasi flip-flopping flow pattern for l = 0.7 to 1.9, modulated synchronized flow pattern for l = 2 to 4.1 and quasi-periodic flow pattern for l = 4.2 to 10 while non-synchronized flow pattern is observed for staggered cylinders without plates at g = 2.5. The flow patterns variation is found to be directly linked with variations in Strouhal number (St) of both cylinders. The fluid force parameters decreased significantly with increasing length of plates as compared to two staggered cylinders without plates. In particular, mean drag coefficient (CDmean) reduces maximum up to 91% at l = 0.8, root-mean-square value of drag coefficient (CDrms) reduces up to 82% at l = 0.1, root-mean-square value of lift coefficient (CLrms) reduces up to 94% at l = 0.3, St reduces up to 72% at l = 10, the amplitude of drag coefficient (CDamp) reduces up to 78% at l = 0.8 and amplitude of lift coefficient (CLamp) reduces up to 87% at l = 0.2. The plates are found more effective in controlling the flow around the second cylinder as compared to the first cylinder. This study also reveals that at some plate lengths, instead of reduction, an increase in hydrodynamic force values occurred compared to the uncontrolled case.

Hydrodynamic and thermal behavior of tandem, staggered, and side-by-side dual cylinders

This study investigates the impact of arrangement of two cylinders on their flow-induced vibrations (FIV) and heat transfer behavior at a Reynolds number of 100. Both cylinders were allowed to vibrate in two degrees of freedom (2DOF), encompassing streamwise and transverse directions. The arrangement of identical circular cylinders was varied across tandem (α = 0°), staggered (α = 30°, 45°, 60°), and side-by-side (α = 90°) configurations, at a constant center-to-center distance of 6D. The cylinders were heated at a fixed temperature to observe the forced convection heat transfer behavior under the influence of 2DOF FIV. To observe the FIV, the reduced velocity was varied from Ur = 0 (stationary cylinders) to 14. Results unveiled cylinder response sensitivity, encompassing vibration and heat transfer, with respect to reduced velocities and arrangements. Tandem arrangement exhibited the greatest vibrations for both cylinders. While lower drag was experienced in tandem for cylinder 2 (C-2), it escalated in staggered positioning. Both cylinders experienced lock-in between Ur = 6 and 8 for all arrangements, involving significant transverse vibration amplitudes. Maximum streamwise vibration reached 6.07% of the maximum transverse vibration for C-2 and 2.34% for C-1. Distinct slender “figure-8” and “oval-shaped” cylinder trajectories emerged, accompanied by diverse vorticity patterns in cylinder wakes across arrangements. For α = 60°, C-2 experienced 75.3% lower transverse vibration and 9.4% higher average Nusselt number compared to tandem setup. Overall, a pronounced correlation emerged between cylinder hydrodynamic behavior and heat transfer characteristics, evident through cylinder vibration, vortex shedding, average Nusselt number, and temperature distribution results.

Transverse vortex-induced vibration of two elliptic cylinders in tandem: Effects of spacing

Renewable energy converters, such as bio-inspired fluttering foils, are gaining popularity due to their eco-friendly properties. However, the system with multiple objects has received scant attention. Here, we analyze how spacing influences the transverse (one-degree-of-freedom) vortex-induced vibration of two tandem identical elliptic cylinders at a constant Reynolds number by employing a wide range of reduced velocities (Ur∈[2,14]) and space ratios (L∗∈[2,6]). The incompressible Navier–Stokes equations are solved using the overset mesh method in the OpenFOAM® library. The findings indicate that the wake structure goes through eight distinct wake modes, as well as two gap flow patterns (reattachment and co-shedding). Vibrational responses, force parameters, and flow patterns determine three spacing configurations. At a small spacing (L∗=2), the upstream cylinder (UC) has the traditional lock-in (the frequency ratio fy/fn≃0.95–1.05) at the reduced velocity (Ur≃7), and the downstream cylinder (DC) has a narrow lock-in region around Ur≃9. However, the UC has a wide soft-lock-in (the synchronization region of fy/fn≃1.15) at high reduced velocities (Ur≃8–10). Here, the transverse vibrations of both cylinders, but especially the DC, reach relatively high amplitudes. At a moderate spacing (L∗=3), the UC bears a lock-in zone analogous to a single cylinder with the same mass ratio, while the DC shows a vast soft-lock-in zone (Ur≃8–14). At a large spacing (L∗=4, 5, and 6), the amplitude of the DC is often larger than that of a single cylinder when it is in the lock-in region. The DC exhibits a peak in amplitude at Ur = 7 and a wake-galloping region for Ur > 12.

Investigation of a Near-Field Cylinder Wake in the Subsonic, Transonic, and Supersonic Regimes

The near wake of a circular cylinder in a high-Reynolds-number regime is investigated using the particle image velocimetry technique for an inflow Mach number spanning 0.3 to 2. The mean flow and turbulent kinetic energy field for different Mach number cases are presented. Furthermore, the influence of the Reynolds and Mach number effects is examined based on the mean separation point along the cylinder surface, which is extracted from complementary schlieren visualization measurements, and the literature. The wake width for the supersonic inflow case is found to be an order of magnitude smaller physically than the subsonic case with an identical cylinder diameter. Additionally, the swirl strength criterion is used to identify the eddies present within the wake, and the eddy size and convection velocity are characterized based on the spatiotemporal correlations. The result suggests that the mean wake features for the subsonic and supersonic cases are very different. Moreover, the interaction of eddies generated at the cylinder’s top and bottom shear layers leads to the large-scale features present in the wake, and the differing paths followed by the eddies between the subsonic and supersonic cases are responsible for the variation in the observed wake width.

A model of describing creep strains and porosity evolution for a hollow cylinder affected by internal gas pressure

Two plane-strain states of two identical hollow cylinders are considered, where one is made of a material with porosity evolution and the other is made of an incompressible material. For each hollow cylinder, the process of inflation begins from an undeformed state and ends as soon as the external boundary radius reaches a certain set value. In the assumption that the porosity increases and reaches its highest value at the outer boundary radius, the two hollow cylinders are compared in terms of their strains and stresses.

Flow-induced vibration fatigue damage of two unequal-diameter flexible cylinders in side-by-side and tandem arrangements

Flow-induced vibrations (FIVs) are the indispensable factor causing the fatigue damage and failure for multi-cylindrical structures in offshore engineering. Mutual interferences between unequal-diameter cylinders complicate the fatigue behaviors. In this paper, an experiment was conducted on two flexible cylinders with a diameter ratio d/D of 0.5 (d and D denote the diameter of small and large cylinders) in uniform flow to investigate their fatigue damage characteristics. Two typical arrangements of side-by-side arrangement and tandem arrangement with a center-to-center spacing ratio P/d = 6.0 (P refers to the center-to-center distance between two cylinders) were examined. The results indicate that the fatigue damage is considerably affected by the arrangement and the diameter ratio. For the side-by-side arrangement, the small cylinder suffers from more serious fatigue damage in the CF direction due to the continuous impingement of the stable biased gap flow. However, the fatigue of the large cylinder is insensitive to the presence of the small cylinder. In a tandem arrangement, the wake shielding effect of the large cylinder located upstream is pronounced, resulting in a significant alleviation in the fatigue damage of the small cylinder. The wake inhibitory effect of the large cylinder is more prominent compared with that of two identical cylinders. The upstream large cylinder behaves analogously to the isolated cylinder. However, its CF fatigue damage is restrained in a few cases of 16.28 ≤ Vr ≤ 18.79 because the vortex shedding frequency is suppressed by the downstream small cylinder. On the other hand, when the small cylinder is located upstream, the wake shielding effect somewhat reduces the IL vibration of the large cylinder. The upstream small cylinder in this unequal-diameter experiment undergoes similar fatigue damage to the cylinder in the equal-diameter experiment.

NEW PIDHID UP TO THE MOVEMENT OF FIRE SAFETY WATER SYSTEMS

When obtaining estimates that characterize the level of fire safety of the hydrogen storage and supply system, there is an error due to the subjective nature of its occurrence. It is noted that it is possible to weaken the influence of the subjective nature on these estimates by using the probabilistic characteristics of failure of the main elements of the hydrogen storage and supply system. Such basic elements include a gas generator. It is shown that the diffusion processes between the hydroreactive sample and the liquid - water are accompanied by the appearance of gas bubbles located on the reacting surface. This process - chemical boiling is characterized by internal characteristics. Internal characteristics were obtained experimentally for hydroreactive samples based on sodium aluminum hydride, which are approximated by polynomials of the fourth order and represent the dependence of the diameter of gas bubbles and the generation frequency on the diameter of the reacting surface. It is noted that the characteristics of the gas generator depend on the orientation of the reacting surfaces of the hydroreactive sample. The growth rate of basic bubbles practically does not depend on the diameter of the reacting surface, and the size of this surface for the vertical arrangement of the reacting surface is several percent larger than for its horizontal arrangement. The most unfavorable mode of gas generation is the case when the reactive surface of the hydro-reactive sample is oriented downwards. It is shown that increasing the reliability of the gas generator of the hydrogen storage and supply system is possible due to the implementation of a hydroreactive sample with a polylike one - a passive method and due to the formation of hydrodynamic forces acting on gas bubbles - an active method. These recommendations are embodied on the example of a hydrogen storage and supply system with vibrational movement of a hydroreactive sample, which is made in the form of a set of identical long cylinders assembled in a mesh cassette. Keywords: water saving and supply system, gas generator, fire safety, reliability.

Electromagnetic energy harvesting via flow-induced vibration of flexible diaphragm in the presence of square cylinders at varied incidence angles: An experimental investigation

This study designs an electromagnetic energy harvester that uses a magnet in translation within a coil to harness energy from flow-induced vibrations when wall confinement affects a change in the wake formation behind a bluff body. An attached permanent magnet surrounded by a coil is attached to a flow channel with a flexible diaphragm, and a square cylinder acts as the bluff body that generates a vortex-induced street, thereby oscillating the diaphragm and generating electrical energy. The main novelty presented in the current investigation is developing a quick and efficient way of capturing fluid energy for practical applications, at the cost of augmented mechatronical complexity. Fluid flow and electromagnetic induction convert flow energy into electrical energy, and the influences of the Reynolds number (Re = 3000, 4000, and 5000) and the position of square cylinders (X*=X/D) on the dynamic characteristics are considered. As a result of different incidence angles (α) and spacing between two identical square cylinders (L*=L/D), Reynolds number and incidence angles have significant effects on the harvesting of energy. Additionally, based on experimental data, an output voltage of 0.04 V can be generated when the excitation pressure oscillates at about 20 Hz. Whether a single square or two identical squares are arranged, the 45-degree incidence angle is the most suitable arrangement for power conversion, and L*=4 can produce maximum energy for all configurations. Finally, the experimental results provide deeper insight into the physics behind the relationship between square spacing, rotation angle, and energy harvesting. Regarding hydroelastic energy extraction, tandem diamond configurations have substantial advantages over square ones. With high amplitudes and high frequencies, tandem diamond cylinders can generate mechanical power even beyond typical circular cross-sections. Furthermore, complementary numerical simulations are presented to provide a solid foundation for the reasoning behind the variation in extracted energy as well as complement the experiment results. By conducting numerical simulations, it is found that changing the incidence angle can significantly alter the flow patterns, which is attributable to the sequential formation of a primary vortex from the lee of the bluff body.

A new look at the sorption kinetics in reference gas standards

The preparation of calibration gas mixtures in cylinders using the gravimetric method (ISO 6142-1) has enabled the production of a wide range of mixtures down to the pmol/mol level with low uncertainties reaching 0.01% relative and beyond. The gravimetric method has limited use however for reactive components that adsorb on the cylinder wall or valve. For such components the adage ‘what comes in = what comes out’ no longer holds. To quantify gas losses in cylinders due to adsorption on the inner surfaces, two methods are typically used: by comparison against other gas mixture preparation methods (e.g. dynamic methods) or by decanting part of a mixture in an identical cylinder followed by cross-comparison. Here we present a new method to elucidate the sorption dynamics based on the use of isotopes (here 12C-methanol and 13C-methanol isotopes). The amount fraction evolution of both isotopes in gas phase is followed in time using laser spectroscopic methods. This way, the kinetics of desorption (mainly 13C-methanol) and adsorption (12C-methanol) can be followed in time. In this paper we will present the results from a pilot study on methanol mixtures at trace amount fractions prepared in different cylinder materials and treatments.

Numerical investigations of two vibrating cylinders in uniform flow using overset mesh

Abstract In this research, flow around two vibrating cylinders in a tandem arrangement is simulated at Reynolds number Re = 200 using the dynamic overset mesh technique in finite volume-based commercial software. This investigation aims to study the combined influences of the spacing between the two identical circular cylinders and their excitation frequency in the flow. The cylinders are excited by a transverse forced vibration in a uniform cross-flow by applying a simple harmonic motion. The gap distance between the vibrating cylinders is chosen to be L/D = 1.5 and 4, and the vibration amplitude is kept constant at A/D = 0.25. The study focuses on three frequency ratios of the cylinders’ excitation frequency to Strouhal shedding frequency of the single stationary cylinder f e/f s = 0.8, 1.0, and 1.2. Simulation results showed that the flow characteristics over the two vibrating circular cylinders differ from that of a single vibrating cylinder. Also, it is observed that the lock-in state (resonance) for the two vibrating cylinders and the vortex wake patterns are highly affected by the gap distance between cylinders and the excitation frequency.

Flow-induced vibration (FIV) fatigue damage characteristics of two unequal-diameter flexible cylinders in a staggered arrangement

In offshore engineering, fatigue damage caused by flow-induced vibrations (FIVs) presents a considerable and potential threat to flexible cylindrical systems during their service lifetime. Through FIV experiments, this paper estimates and analyzes the fatigue damage of two unequal-diameter cylinders with diameter ratio d/D = 0.5 (where d and D denote the diameter of small and large cylinders) and the center-to-center spacing ratio P/d = 6 (where P denotes the center-to-center distance between two cylinders) through the S–N curve and fatigue damage accumulation methods in the DNV standard. Ten staggered configurations were studied, including two relative positions and five stagger angles (θ = 15°, 30°, 45°, 60°, and 75°). The fatigue damage evaluation results indicate that the FIV fatigue damage is highly affected by the stagger angle and relative position of the two cylinders. The FIV fatigue behavior of the two unequal-diameter cylinders is quite different from that of the two identical cylinders. When the large cylinder is located upstream, its wake shielding effect on the small cylinder is predominant at small stagger angles, so both the IL and CF fatigue damage of the downstream small cylinder is significantly suppressed, especially when Vr ≤ 16.28. But as the stagger angle is increased, the wake-induced flutter can aggravate the fatigue damage of the downstream small cylinder. Moreover, the CF fatigue damage of the large cylinder is decreased at small angles due to the vortex-shedding frequency suppression of the small cylinder and the fatigue damage of the large cylinder in the IL direction is analogous to that of the isolated cylinder and is negligibly affected by the small cylinder. When the small cylinder is located upstream, the IL FIV fatigue damage of the downstream large cylinder is approximately unaffected due to the narrow wake of the small cylinder. However, the CF fatigue damage of the large cylinder is greatly reduced at small stagger angles.

On the galloping cross-flow vibration responses of three in-line square cylinders

Galloping cross-flow vibration responses of three in-line identical square cylinders are numerically studied for the mass ratio m*=2, streamwise gaps Lx=3B and 5B, reduced velocity U*=3−50, and Reynolds numbers Re = 150 in two dimensions (2-D) and 2000, where the flow is three-dimensional (3-D). Here, B is the side of the cylinder. An isolated cylinder does not gallop since the mass ratio m*=2 is less than the critical value in the Re = 150 flow, whereas for the three in-line bodies, galloping instability is triggered at the upstream cylinder due to the interference effect caused by the presence of downstream bodies. The interaction with the wake of galloping upstream cylinder promotes galloping instability for the two downstream cylinders almost immediately at Re = 150. In the three-dimensional wake at Re = 2000, downstream cylinders interact with less coherent Karman vortices shed by the galloping upstream cylinder, compared to the 2-D case. This phenomenon leads to the delayed on-set of galloping response for the first downstream cylinder, while the second one never gallops.

Vortex-induced vibrations of tandem diamond cylinders: A novel lock-in behavior

This paper presents a comprehensive numerical investigation of the undamped, simultaneous in-line, and transverse flow-induced vibrations of two identical diamond cylinders (of cross-stream length D) in a tandem arrangement at a low Reynolds number (= 100) in uniform flow, using a stabilized space–time finite-element formulation. The study focuses on the effects of cylinder proximity and shape, considering diamond cylinders with a mass ratio of 10 and a separation distance of 5D and varying the reduced velocity from 1 to 20. The results reveal distinct lock-in behavior for the upstream and downstream cylinders, with a low-frequency extended lock-in phenomenon observed for the downstream cylinder. The motion trajectories of both cylinders exhibit a distinctive “raindrop-shaped” pattern. Notably, the synchronization zone shows a non-zero mean lift for a narrow range of reduced velocity. The study also identifies three distinct modes of vortex arrangement in the gap region between the cylinders. Comparing the findings for tandem diamond cylinders with those for single diamond and tandem square cylinders provides further evidence of the significant impact of proximity and shape on the vibration characteristics of the cylinders.