Circular Cylinders Of Different Diameters Research Articles

Experimental investigation of surface pressures, velocities, and dynamic structural analysis of tornadic winds on a luminary pole

Several engineering and media reports have demonstrated that luminary and lighting poles are susceptible to tornadic wind actions. This paper provides the first dynamic structural analysis of a 1:50 geometrically scaled model of a generic luminary pole of a circular cross-section tested under transient wind loads caused by translating tornado-like vortices (TLVs). The physical experiments were performed in the WindEEE Dome tornado simulator at Western University (Canada). The tornadic wind actions on the pole are also compared against the reference atmospheric boundary layer (ABL) wind gust with the mean recurrent period of 50 years. Three different positions of the luminary pole in respect to the TLV path were considered: (1) TLV center passing over the pole; (2) TLV core radius passing over the pole; and (3) an intermediate case in which the pole was positioned between the TLV center and the core radius. In all cases two circular cylinders of different diameters were used to simulate two different cross-sections of an actual luminary pole. Our study demonstrates that luminary poles are more susceptible to tornadic wind actions compared to ABL winds. The tip displacements of the pole were larger in the TLVs and the direction and magnitude of the displacements were dependent on the relative positions of the TLVs and the luminary pole. The highest wind forces were observed in the regions characterized by strong tangential wind speeds. The entire luminary pole was subjected to negative pressure coefficients during the TLV passage. However, our structural analysis showed that the pole always stayed in the elastic region of deformation and there was no permanent bending or collapse of the structure.

Experimental investigation of downstream cylinder vibrations caused by FIV in the presence of upstream stationary cylinder

The mechanism of flow induced vibrations (FIV) exists in many engineering applications and plays a significant role. In offshore engineering, the risers subjected to flow induced vibrations. In this study, two circular cylinders of different diameters are arranged in tandem manner. In cross-flow transverse direction, the upstream cylinder is fixed, while the downstream cylinder is subjected to vibrations. This study carries out experiments in wind tunnel, which focuses on significant vibration-galloping. Variable mass-damping ratio is used to achieve the critical velocity corresponding to onset galloping vibration. In the present study, the diameter ratio is 0.4 and the gap L is 1.5D, and 3.5D. In the wind tunnel experiments, by changing the mass of the vibrating cylinder, the corresponding values of damping ratio, results in variable mass damping ratio m*ζ. For each value of m*ζ, the amplitude, frequency at every reduced velocity will be obtained at first, the critical velocity and stability map will be summarized. At static area between lock-in and galloping (desynchronization branch), a uniform initial displacement was set to get the total damping ratio. This study also investigates the relationship among the total damping ratio, m*ζ and critical velocity.

Higher-Order Turbulence Around Different Circular Cylinders Using Particle Image Velocimetry

Abstract Wakes and higher-order turbulence around circular cylinders of different diameters are investigated using particle image velocimetry measurements. The cylinder Reynolds number (Red) is defined by the depth-averaged velocity, cylinder diameter, and kinematic viscosity. The influence of Red on third-order moment of velocity fluctuations, turbulent kinetic energy (TKE) flux, TKE budget, and turbulent length scales are presented. The intermittency factor (IF) and quadrant analysis around the cylinders are discussed for Red values ranging from 12,600 to 21,000. The energy budget mostly near free surface upstream and near-bed downstream is changed due to Red. Stream-wise and transverse TKE fluxes decreased significantly with Red, but not the vertical flux. Stream-wise skewness changed sign from positive to negative at a certain critical distance downstream, while vertical skewness showed reversed effect with Red. Negative stream-wise skewness and positive vertical skewness indicate the occurrence of ejection events. On the downstream, the production and dissipation rates increased with Red, whereas an opposite trend was observed for dissipation only on the upstream. Increase of Red led to an increase in the Kolmogorov length-scale much higher on the upstream than the downstream, whereas it showed depleting effect on Taylor's length-scale on the upstream and an increasing effect on the downstream. Ejection and sweep events were more prominent in the downstream near the cylinder than upstream with higher values of shear stress on the downstream. The sum of the shear stress contributions of all quadrant events increased consistently with an increase in Red near the cylinder.

The predominant frequency for viscous flow past two tandem circular cylinders of different diameters at low Reynolds number

Viscous flow past two circular cylinders in tandem arrangement is numerically investigated at a typical Reynolds number of 200 which is based on the diameter of the downstream cylinder. The non-dimensional diameter of the downstream cylinder D is fixed to be 1.0, while the non-dimensional diameter of the upstream cylinder d varies from 0.1 to 1.0 with an interval of 0.1. Moreover, the minimal non-dimensional distance between the two cylinders changes from 0.1 to 4.0. The numerical results show that continuous variation of the mean drag coefficient, the lift coefficient, and the lift frequency is observed with the increase in the gap ratio for d/ D = 0.1 and 0.2. Discontinuities are found for the mean drag coefficient, the lift coefficient, and the lift frequency of the downstream cylinder with the increase in gap ratio for d/ D = 0.9 and 1.0. Multiple lift oscillating frequencies of the downstream cylinder can be detected for d/ D = 0.3–0.8 at special gap ratios. Special attention is paid on d/ D = 0.4, which is a typical example for d/ D = 0.3–0.8. The predominant lift frequency of the downstream cylinder is observed to change from fL-1 to fL-2 as the increase in the gap ratio for d/ D = 0.4, which have not been previously detected. However, the predominant drag frequency of the downstream cylinder is found always to be fD-3 in present investigation scope. Moreover, a conclusion that fD-3 = fL-1 + fL-2 can be obtained.

Wake-Induced Vibrations of Tandem Circular Cylinders of Different Diameters

Wake-induced vibrations (WIV) of two circular cylinders in tandem arrangement of different diameters (larger downstream cylinder) has been analyzed in the present work. The ratio of the diameter of first cylinder to that of the second cylinder (D1/D2) is kept constant at 0.8. The cylinder centers are separated by a distance S (= 5D1). The computations were carried out at Reynolds number (Re) = 100 over a range of reduced speed (U*). The fluid was assumed to be incompressible and flow to be two-dimensional. The flow equations were discretized using stabilized finite-element method and solved iteratively by Generalized Minimal RESidual (GMRES) technique. In the present work, the upstream cylinder is kept stationary while the downstream cylinder is allowed to traverse only across the flow. The observations focus the response, aerodynamic coefficients and flow features.

Vortex shedding in the flow around two side-by-side circular cylinders of different diameters

In this paper, the 3-D turbulent flow around two side-by-side circular cylinders of different diameters, at sub-critical Reynolds number (Re = 3900), is numerically simulated by the large eddy simulation (LES). The spacing ratios (T/D) between the two cylinders are considered in four cases (T/D = 1.2, 1.5, 1.8 and 2.7) to study the vortex shedding and turbulent properties in the flow field. The main results are focused on the drag and lift coefficients, the vortex shedding frequency, the coherent structure, and the scale properties. It is shown that when T/D is equal to 1.2, the vortex shedding of the main cylinder is strongly suppressed by the small cylinder, the drag and lift coefficients of the main cylinder are smaller than those in other three cases. While T/D is equal to 1.5, the vortex shedding of the main cylinder can be improved, the drag and lift coefficients of the main cylinder are larger than those in other three cases. The empirical mode decomposition (EMD) method is applied to decompose the velocity signals traced by the LES. It is shown that there is a linear relationship between the mean period and the mode in the semi-log coordinates. The vortex shedding period of the main cylinder is consistent with the period of the restructured coherent structures quantitatively.

Numerical Investigation of Flow and Heat Transfer Characteristics of Two Tandem Circular Cylinders of Different Diameters

ABSTRACTUnsteady laminar flow and heat transfer characteristics from a downstream cylinder of two tandem circular cylinders of different in diameters are numerically investigated. The working fluid is air, and the downstream cylinder is isothermal while the upstream cylinder is kept adiabatic. Two-dimensional numerical simulations are carried out for Reynolds numbers of 100 and 200. The ratio of the upstream to downstream cylinder diameters (diameter ratio) and the ratio of the gap distance to the downstream cylinder diameter (gap ratio) are considered in the range of 0.3 to 2 and 0.5 to 4, respectively. Numerical solutions are obtained using the FLUENT® software. The flow parameters such as the rms lift/drag coefficients and Strouhal numbers are computed and analyzed for the diameter ratio and gap ratio intervals investigated. The iso-vorticity lines and isotherms are also generated to understand, identify and analyze the flow and heat transport characteristics. Four basic flow structures are observed and classified as (i) over-shoot, (ii) symmetric-reattachment, (iii) front-side reattachment and (iv) co-shedding flow. The critical spacing, which marks the minimum gap spacing for the vortex formation to begin, depends on the diameter ratio and Reynolds number, and it decreases with increasing Reynolds number. The convective heat transfer phenomenon is observed to be strongly influenced by diameter ratio, gap ratio and Reynolds number. The mean and the local Nusselt number along the perimeter of isothermal cylinder are computed and discussed in connection with the flow characteristics.

Hydrodynamics and vortex shedding characteristics of two tandem cylinders of different diameters in steady flow

Viscous flow past two tandem circular cylinders of different diameters is numerically investigated by using finite volume method. The diameter ratio between the two cylinders ranges from 0.1 to 1.6. The Reynolds number based on the diameter of cylinders is 800 for the large cylinder and 100 for the smallest cylinder. The spacing between two tandem cylinders ranges from 0.1 to 1.6 times the diameter of the large cylinder. Identified from the numerical results for all the cases of tandem configurations, spacing ratio* (S/d) = 1.5 is the critical point. The root mean square lift coefficient on both of the two cylinders abruptly increases at the critical point. The values of the fluctuating forces acting on the large cylinder are generally lower than those on a single cylinder. Three different wake modes are identified based on the vortex shedding characteristics behind two tandem cylinders, the one wake mode, the transitional mode and the reappearance mode. “Attachment” has been found in the transitional mode for the diameter ratio of d/D = 0.75 at the critical point. The numerical results are powerful basis for design of piggyback pipeline.

Three-dimensional flow around two circular cylinders of different diameters in a close proximity

Flow past two cylinders of different diameters in close proximity is simulated numerically for a constant diameter ratio of 0.45, a gap ratio of 0.0625, and a Reynolds number of 1000 (defined using the diameter of the main cylinder). The effect of the position angle α of the small cylinder relative to the large one on force coefficients and wake flow patterns are studied. Depending on the position angle α of the small cylinder, four wake flow modes are identified: the upstream interference mode for α = 0°, 22.5°, and 45°, the intermittent attached gap flow mode for α = 67.5° and 90°, the attached gap flow mode for α = 112.5° and 135°, and the wake interference mode for α = 157.5° and 180°. The RMS lift coefficients of both cylinders are reduced significantly compared with that of a single cylinder, regardless of the position angle of the small cylinder. Although the variation trends of the mean drag and lift coefficients with the position angle of the small cylinder obtained from the two-dimensional (2D) and three-dimensional (3D) simulations are similar, the 2D simulations overestimate the mean drag coefficient, the RMS drag and lift coefficients compared with those obtained from the 3D simulations.

Numerical simulation of low-Reynolds number flows past two tandem cylinders of different diameters

The flow past two tandem circular cylinders of different diameters was simulated using the finite volume method. The diameter of the downstream main cylinder (D) was kept constant, and the diameter of the upstream control cylinder (d) varied from 0.1D to D. The studied Reynolds numbers based on the diameter of the downstream main cylinder were 100 and 150. The gap between the control cylinder and the main cylinder (G) ranged from 0.1D to 4D. It is concluded that the gap-to-diameter ratio (G/D) and the diameter ratio between the two cylinders (d/D) have important effects on the drag and lift coefficients, pressure distributions around the cylinders, vortex shedding frequencies from the two cylinders, and flow characteristics.

Lock-in study of two side-by-side cylinders of different diameters in close proximity in steady flow

Lock-in of the vortex-induced vibration of two side-by-side circular cylinders of different diameters (diameter ratio d/D=0.1) is investigated numerically. The cylinders are located in close proximity and free to oscillate in the cross-flow direction. The initial gap between the two cylinders is set the same as the small cylinder diameter (d). The mass ratios of both cylinders (m⁎) are fixed to be 5 and the damping ratios are small enough to be negligible. Simulations are first carried out for two cases where the large-to-small-cylinder natural frequency ratio is 1. Case 1 is focused on the lock-in of the large cylinder and Case 2 is focused on the lock-in of the small cylinder, which is far narrower than that of the large cylinder. Then simulations are carried out at a natural frequency ratio (small-to-large-cylinder) of 0.1, where both cylinders are expected to lock on to their own natural frequencies (referred to be Case 3). The interference between the two cylinders under these conditions is investigated in detail. The widening of the lock-in range of the reduced velocities for the large cylinder in Case 1, the beating behavior of the small cylinder in its lock-in range in Case 2 and the dual lock-in behavior of the small cylinder during the simultaneous lock-in of both cylinders in Case 3 are some of the key findings of this study.

Vortex induced vibration and vortex shedding characteristics of two side-by-side circular cylinders of different diameters in close proximity in steady flow

This paper presents results of a numerical study of vortex-induced vibrations of two side-by-side circular cylinders of different diameters in steady incompressible flow. The two-dimensional Reynolds-averaged Navier–Stokes equations with a SST k–ω turbulence model are solved using the Petrov–Galerkin finite element method and the Arbitrary-Lagrangian–Eulerian scheme. The diameter ratio of the two cylinders is fixed at 0.1 and the mass ratio of both cylinders is 5.0. Both cylinders are constrained to oscillate in the transverse direction only. The Reynolds number based on the large cylinder diameter and free stream velocity is fixed at 5000. The effects of the reduced velocities of the cylinders on the vibration amplitude and vortex shedding regimes are investigated. It is found that for the range of parameters considered, collision between the two cylinders is dependent on the difference of the reduced velocities of the cylinders. Presence of the small cylinder in the proximity of the large one appears to have significant effects on the vortex shedding regime and vibration amplitude of the large cylinder.

Drag Coefficients Acting on Two Tandem Cylinders of Different Diameters

The flow past two tandem circular cylinders of different diameters is simulated by using a finite volume method. The diameter of the downstream main cylinder is kept constant, and the diameter ratio between the upstream control cylinder and the downstream one is varied from 0.1 to 1.0. The Reynolds number based on the diameter of the downstream main cylinder is 100 and 150. The gap between the control cylinder and the main cylinder ranges from 0.1 to 4.0 times the diameter of the main cylinder. It is concluded that the gap ratio and the diameter ratio between the two cylinders have important effects on the drag coefficients and flow characteristics.

Vortex Shedding with Fluid Mechanics from Two Cylinders of Different Diameters in a Tandem Arrangement

The vortex shedding from two circular cylinders of different diameters in a tandem arrangement is numerically investigated at a Reynolds number of 100 and 150. The studied Reynolds number based on the diameter of the downstream main cylinder. The diameter of the downstream main cylinder was kept constant, and the diameter ratio between the upstream control cylinder and the downstream one was varied from 0.1 to 1.0. The gap between the control cylinder and the main cylinder ranged from 0.1 to 4.0 times the diameter of the main cylinder. It is concluded that the gap ratio and the diameter ratio between the two cylinders have important effects on vortex shedding from two cylinders of different diameters in a tandem arrangement.

Numerical simulation of vortex-induced vibration of two circular cylinders of different diameters at low Reynolds number

Two-degree-of-freedom Vortex-Induced Vibration (VIV) of two rigidly coupled circular cylinders of different diameters at a low Reynolds number of 250 is investigated numerically. While the diameter ratio and the mass ratio are kept constant, the study is focused on the effect of the position angle of the small cylinder on the lock-in regime of the VIV. Simulations are carried out for position angles α of the small cylinder ranging from 0° to 180° with an interval of 22.5° and the reduced velocities ranging from 1 to 15 with an increment of 1. In order to find the effect of the gap between the two cylinders on the vibration, two gap-to-diameter ratios (0 and 0.2) are considered. It is found that compared with a single cylinder case, the lock-in regime of the reduced velocity is widened significantly when the position angle of the small cylinder is α = 0°, 22.5°, 90°, or 112.5°. Pulsed beating phenomenon characterized by regular vibration with occasional high-amplitude disturbances at regular or irregular intervals is observed at G = 0 and α = 90°. At α = 135°, more than one lock-in regimes are observed in the computed range of reduced velocity for both gaps (G = 0 and 0.2). Setting a small gap (gap-to-diameter ratio of 0.2) between the two cylinders mitigates the vibration by narrowing the lock-in regime and reducing the vibration amplitude.

Hydrodynamic forces on dual cylinders of different diameters in steady currents

Abstract Turbulent flow past two circular cylinders of different diameters is numerically investigated. The two-dimensional Reynolds-averaged Navier–Stokes equations are solved by using a finite element method with a k–ω turbulence closure. Following a relevant numerical model validation process, effects of cylinder gap-to-diameter ratio, the angular position of the smaller cylinder and the diameter ratio of cylinders on the vortex shedding and the forces on the cylinders are investigated using the numerical model. It is found that the relative position of the small cylinder has significant effects on the hydrodynamic force and vortex shedding characteristics of the cylinders.

Numerical simulation of viscous flow past two circular cylinders of different diameters

Viscous flow past two circular cylinders of different diameters is simulated by using a finite element method. The diameter ratio between the small cylinder and the large one is 0.25. The Reynolds number based on the diameter of the cylinders is 500 for the large cylinder and 125 for the small cylinder. The gap between the small cylinder and the large cylinder ranges from 0.05 to 1.0 times the diameter of the large cylinder. The position angle of the small cylinder relative to the flow direction ranges from 0 to π. The effects of the gap ratio between the two cylinders and the position angle of the small cylinder on drag and lift coefficients, pressure distributions around the cylinders, the vortex shedding frequencies from the two cylinders and flow characteristics are investigated. The magnitudes and frequencies of the fluctuating forces acting on the two cylinders are compared with those on a single cylinder of an equivalent diameter.

Interactive flow around two circular cylinders of different diameters at close proximity. Experiment and numerical analysis by vortex method

Experimental investigations and numerical analysis were carried out to clarify the behavior of an interactive flow around two circular cylinders with different diameters. In particular, the reattachment that the separated shear layer from the main cylinder reattaches on the rear surface by Coanda effect was noted. The results obtained were as follows. Intermittency of the reattachment was found in the present numerical calculation, and was confirmed experimentally. The calculated values of time-averaged fluid forces agreed well with those of experiments, and the qualitative characteristics of calculated Strouhal numbers were coincident with those of experiment.

Interactive Flow around Two Circular Cylinders of Different Diameters at Close Proximity. Experiment and Numerical Analysis by Vortex Method.

Experimental investigations and numerical analysis were carried out to clarify the behavior of an interactive flow around two circular cylinders with different diameters. In particular, the reattachment that the separated shear layer from the main cylinder reattaches on the rear surface by Coanda effect was noted. The results obtained were as follows. Intermittency of the reattachment was found in the present numerical calculation, and was confirmed experimentally. The calculated values of time-averaged fluid forces agreed well with those of experiments, and the qualitative characteristics of calculated Strouhal numbers were coincident with those of experiment.

Interaction of flow structures within bistable flow behind two circular cylinders of different diameters

The bistable flow of two circular cylinders of diameter ratio 2:1 was investigated. Based on the quantitative and qualitative measurements, two modes of flow are observed. Interactions of the adjacent gap-side vortices with the outer vortices and the pairing of outer vortices in both modes form the important mechanisms for the development of flow structures and wakes further downstream.