Cylinders In Tandem Arrangement Research Articles

Numerical investigation of mixed convection heat transfer from two isothermal circular cylinders in tandem arrangement: buoyancy, spacing ratio, and confinement effects

This paper presents a two-dimensional numerical study for mixed convection in a laminar cross-flow with a pair of stationary equal-sized isothermal cylinders in tandem arrangement confined in a channel. The governing equations are solved using the control volume method on a nonuniform orthogonal Cartesian grid, and the immersed boundary method is employed to identify the cylinders placed in the flow field. The numerical scheme is first validated against standard cases of symmetrically confined isothermal circular cylinders in plane channels, and grid convergence tests were also examined. The objective of the present study was to investigate the influence of buoyancy and the blockage ratio constraint on the flow and heat transfer characteristics of the immersed cylinder array. Using a fixed Reynolds number based on cylinder diameter of \(Re_{D} = 200\), a fixed value of the Prandtl number of \(Pr = 7\), and a blockage ratio of \(D/H = 0.2\), all possible flow regimes are considered by setting the longitudinal spacing ratio (\(\sigma = L/D\)) between the cylinder axes to 2, 3, and 5 for values of the buoyancy parameter (Richardson number) in the range \(-1\le Ri\le 4\). The interference effects and complex flow features are presented in the form of mean and instantaneous velocity, vorticity, and temperature distributions. The results demonstrate how the buoyancy, spacing ratio, and wall confinement affect the wake structure and vortex dynamics. In addition, local and average heat transfer characteristics of both cylinders are comprehensively presented for a wide range in the parametric space.

Numerical study on phase change of water flowing across two heated rotating circular cylinders in tandem arrangement

The problems of fluid flow and heat transfer phenomena over an array of cylinders are quite prominent in fluid dynamics and industry applications. The current work focuses on fluid flow and heat transfer analysis over two heated rotating cylinders arranged in tandem. The flow of water over heated cylinders faces a phenomenon of phase change from liquid (water) to vapor phase (steam). The mechanism of this phase change is studied through a numerical simulation supplemented with verification of the code and validation. The problem is simulated when flows from two cylinders in a tandem arrangement become interacting and non-interacting. The Eulerian model is used during simulation to comprehend the multiphase phenomena. The volume fractions of both the phases such as water and vapor and heat transfer coefficients of both the cylinders have been computed and presented as findings of the problem. The mass and heat transfer mechanism is unidirectional from one phase to the other phase. The vapor fraction of each phase is to be observed and compared when three different rotations are given to the two cylinders immersed in a turbulent flow of water.

Multi-mode vortex and wake-induced vibrations of a flexible cylinder in tandem arrangement

Experiments with a flexible cylinder of circular cross-section towed behind a stationary circular cylinder at various distances are described in this paper. The dynamics of the model immersed in the wake of the leading one are fully characterised after data processing and computation of amplitude and frequency responses, as well as modal content as a function of reduced velocity. Reduced velocity was controlled by changing the towing speed of the system and by adjusting different pre-tensions on the model.The amplitude response of the model has been found to be dominated by resonance or lock-in regions in the reduced velocity axis at the different structural modes of the cylinder model. Separation distance does not produce significant qualitative changes in the response amplitudes and frequencies observed when compared to the response of the same cylinder without wake interference. However, there is a clear effect of the incoming wake, because amplitude responses are considerably higher than those expected in isolated cylinders at the same reduced velocities. Also, the response has been found to be more multi-modal with responses made of large amplitude contributions of several adjacent modes.

Numerical Study on Phase Change of Water Flowing Across Two Heated Circular Cylinders in Tandem Arrangement

AbstractThis paper focuses on fluid flow and heat transfer analysis over two heated cylinders arranged in tandem. The flow of water over heated cylinders faces a phenomenon of phase change from liquid (water) to vapor phase (steam). The mechanism of this phase change is studied through a numerical simulation supplemented with verification and validation of the code. The problem is simulated when flows from two cylinders in a tandem arrangement become interacting and noninteracting. The Eulerian model is used during simulation to comprehend the multiphase phenomena. The effect of spacing between these two cylinders and the Reynolds number effect are studied in this paper. The volume fractions of both the water and vapor phases and the heat transfer coefficients of both the cylinders have been computed and presented as findings of the problem.

Effect of Reynolds number on phase change of water flowing across two heated circular cylinders in tandem arrangement

The situations of fluid flow and heat transfer across an array of cylinders have been quite common in fluid dynamics and, particularly, industry applications. One such situation is flow of water over heated cylinders in a tandem arrangement. The flow of water over heated cylinders faces a phenomenon of phase change from liquid (water) to vapor phase (steam).The mechanism of this phase change is studied through a numerical simulation in this project. The Eulerian model is used in the present simulation method to comprehend the multiphase phenomenon. The effect of Reynolds number on the phase change is studied. The phase change of water in an unsteady flow across cylinders has been prominently affected by Reynolds number. Only critical cases have been discussed in this paper. The volume fraction of water and steam is plotted against the position of flow from inlet to exit of the flow domain that is a channel for a particular flow conditions to demonstrate the phenomenon of heat and mass transfer during the flow of water.

A Numerical Study of the Forces on Two Tandem Cylinders Exerted by Internal Solitary Waves

A three-dimensional numerical wave flume is employed to investigate the forces exerted by internal solitary waves (ISWs) on a pair of circular cylinders in tandem arrangement, using large-eddy simulation (LES) model. The effect of the centre-to-centre distance (L) ranging from 1.5 to 5 diameters (D) is studied for various ISWs amplitudes (ηa) in the two-layer fluid system. Vertical-averaged vorticity distribution and vertical-averaged pressure gradient distribution in each layer are presented to investigate the different hydrodynamic interference between cylinders and the ISWs forces on each cylinder at variousL. Furthermore, the force behaviors of the two cylinders are also compared with that of an isolated cylinder in the same environment. The interaction between the two piles occurs in both layers, and it is found that, for1.5≤L/D<3.5, strong mutual interference appears between two cylinders; for3.5≤L/D<5, the two cylinders continue to influence each other in a weak-interference state; forL/D≥5, the interaction gradually decreases into a noninteracting state. This paper tries to provide some references to structural arrangement of double-cylinder structure and grouped-cylinder structure in stratified flow environment.

Numerical Simulation of Turbulent Flow around Two Cam Shaped Cylinders in Tandem Arrangement

Numerical Simulation of Turbulent Flow around Two Cam Shaped Cylinders in Tandem Arrangement

Numerical simulation of flow past twin near-wall circular cylinders in tandem arrangement at low Reynolds number

Fluid flow past twin circular cylinders in a tandem arrangement placed near a plane wall was investigated by means of numerical simulations. The two-dimensional Navier-Stokes equations were solved with a three-step finite element method at a relatively low Reynolds number of Re = 200 for various dimensionless ratios of 0.25 ≤ G/D ≤ 2.0 and 1.0 ≤ L/D ≤ 4.0, where D is the cylinder diameter, L is the center-to-center distance between the two cylinders, and G is the gap between the lowest surface of the twin cylinders and the plane wall. The influences of G/D and L/D on the hydrodynamic force coefficients, Strouhal numbers, and vortex shedding modes were examined. Three different vortex shedding modes of the near wake were identified according to the numerical results. It was found that the hydrodynamic force coefficients and vortex shedding modes are quite different with respect to various combinations of G/D and L/D. For very small values of G/D, the vortex shedding is completely suppressed, resulting in the root mean square (RMS) values of drag and lift coefficients of both cylinders and the Strouhal number for the downstream cylinder being almost zero. The mean drag coefficient of the upstream cylinder is larger than that of the downstream cylinder for the same combination of G/D and L/D. It is also observed that change in the vortex shedding modes leads to a significant increase in the RMS values of drag and lift coefficients.

Fluid-Structure Coupling between Two Tandem Elastic Cylinders

The paper presents an experimental investigation on characteristics of flow-induced vibrations of two circular cylinders in tandem arrangement. Both cylinders are allowed to vibrate in the cross-flow direction only. The spacing ratio L/D (where L is the spacing between the two cylinder centers and D is the diameter) is varied as 1.2, 1.5, 2.0, 2.5, 3.0, 4.0 and 6.0. Four regimes are identified. In regime I (L/D ≤ 1.5), the two cylinders experience vortex excitation (VE) combined with ‘galloping. In regime II (1.5 <L/D < 2.5), again both cylinders undergo VE followed by galloping, but the VE and galloping are separated. Regimes III (2.5 ≤ L/D ≤ 3.0) and IV (L/D > 3.0) are characterized by separated VE and galloping for the downstream cylinder and only VE for the upstream cylinder. Compared to that of the downstream cylinder, in regime I the vibration amplitude of the upstream cylinder is larger, and in regime II it is larger at a smaller reduced velocity Ur and smaller at a larger Ur. On the other hand, regimes III and IV correspond to a larger vibration amplitude for the downstream cylinder and very smaller amplitude for the upstream cylinder. Vibration of the downstream cylinder is however violent in the former regime and weaker in the latter. The wake structure of vibrating cylinders is demonstrated by PIV measurements.

Numerical investigation of wake modes for flow past three tandem cylinders using the multi-relaxation-time lattice Boltzmann method for different gap spacings

In this paper, the effect of gap spacing on the flow past three square cylinders in tandem arrangement is studied numerically using a 2-D multi-relaxation-time lattice Boltzmann method (MRT-LBM). The Reynolds number is fixed at 75 and variation of the gap spacing is from 0.5 to 17. The results are compared to some earlier published results and found to be in good agreement. Five different wake modes are observed by the increment in the gap spacing. To understand the effect of different gap spacings on the flow-induced forces; a detailed analysis of mean drag coefficient, time signal analysis of drag and lift coefficients, Strouhal number, root mean square values of drag and lift coefficients is presented in this article. In this study, it is observed that the critical gap spacing is 3, its existence and effects on the flow characteristics are also studied.

Flow around two tandem square cylinders near a plane wall

An experimental study has been conducted to investigate the flow around two identical square cylinders in tandem arrangement and placed near a plane wall at a Reynolds number of 6,300. The inter-cylinder spacing ratio was varied from S* = 0.5 to 6, and the cylinder-to-wall gap ratio from G* = 0.25 to 2. Totally, 42 cases were considered to systematically examine the effects of wall proximity and the mutual interference between the two cylinders in the normalized gap–spacing (G*–S*) plane. The flow fields were captured using digital particle image velocimetry, in conjunction with measurements of the fluid forces (drag and lift) acting on the downstream cylinder using a piezoelectric load cell. The results show that the flow is highly dependent on the combined values of G* and S*. Categories relating to G* could be broadly classified as small-gap regime (G* 1) where the wall effects become negligible. Similarly, the flow interference between the two cylinders can be divided into three basic categories as a function of S*, namely, shielding regime at S* 3. Variations of force coefficients, amplitude spectra, Strouhal numbers, and Reynolds shear stress with G* and S* are presented to characterize the different flow regimes.

Wake-induced vibrations of an elastically mounted cylinder located downstream of a stationary larger cylinder at low Reynolds numbers

Two-dimensional numerical simulations of flow past two unequal-sized circular cylinders in tandem arrangement are performed at low Reynolds numbers (Re). The upstream larger cylinder is stationary, while the downstream cylinder has both one (transverse-only) and two (transverse and in-line) degrees of freedom (1-dof and 2-dof, respectively). The Re, based on the free stream velocity U∞ and the downstream cylinder diameter d, varies between 50 and 200 with a wide range of reduced velocities Ur. The diameter of the upstream cylinder is twice that of the downstream cylinder, and the center-to-center spacing is 5.5d. In general, for the 1-dof case, the calculations show that the wake-induced vibrations (WIV) of the downstream cylinder are greatly amplified when compared to the case of a single cylinder or two equal-sized cylinders. The transverse amplitudes build up to a significantly higher level within and beyond the lock-in region, and the Ur associated with the peak amplitude shifts toward a higher value. The dominant wake pattern is 2S mode for Re=50 and 100, while with the increase of Re to 150 and 200, the P+S mode can be clearly observed at some lower Ur. For the 2-dof vibrations, the transverse response characteristics are similar to those presented in the corresponding 1-dof case. The in-line responses are generally much smaller, except for several significant vibrations resulting from in-line resonance. The obvious in-line vibration may induce a C (chaotic) vortex shedding mode for higher Re (Re=200). With regard to the 2-dof motion trajectories, besides the typical figure-eight pattern, several odd patterns such as figure-double eight and single-looped trajectories are also obtained due to the wake interference effect.

Experimental study on the flow around two tandem cylinders with unequal diameters

In this paper, flow around two circular cylinders in tandem arrangement with unequal diameters has been investigated using the particle image velocimetry technique (PIV) in a water channel. The upstream to downstream diameter ratio was kept constant at d/D = 2/3, the centre-to-centre distance was varied from 1.2D to 5D and the Reynolds number was varied from 1200 to 4800. The flow characteristics were analyzed through ensemble-averaged patterns of velocity, vorticity, normalized Reynolds stress contours and streamlines. Based on ensemble-averaged and instantaneous flow fields, different flow patterns, including single-wake-shedding at small spacing ratio, bi-stable flow behavior (alternating behavior of reattachment and vortex shedding) at intermediate spacing ratio and co-shedding pattern at large spacing ratio were observed. The effects of Reynolds number and the centre-to-centre spacing ratio on flow patterns and turbulent characteristics were also investigated. It was found that the diameter ratio appears to have a certain effect on the flow patterns at intermediate spacing ratios, where the reattachment of shear layer depends on the lateral width of the wake flow in the lee of the upstream cylinder. Extensive discussion on the distributions of Reynolds stress and turbulent kinetic energy was presented.

WIV response of tapered circular cylinders in a tandem arrangement: An experimental study

In practical situations, cylindrical structures are arranged in various configurations where they might show different flow induced responses as compared to that for an isolated cylinder. The current paper reports the results of an in-water experimental study dealing with the transverse and streamwise responses of tapered cylinders in tandem arrangements. The results are examined against those for equivalent tandem uniform cylinders. The study can be considered as the first of its kind reported in the open literature. In the present study the upstream cylinder is fixed while the downstream cylinder is elastically mounted. The single degree of freedom vibrating system has a low mass-damping parameter (m*ξ≈0.0408). The Reynolds number, based on the mean diameter of the cylinders, ranges from 1400 to 20,000 and the reduced velocities vary from 2 to 21. Various spacing ratios (S/D) from 2 to 7 are examined.For tapered cylinders in tandem arrangement it is found that unlike uniform cylinders, the amplitude of vibrations does not decrease with the increase of the spacing ratio. The amplitude of the transverse response in the tandem tapered cylinder is slightly higher than that for the uniform cylinder in a tandem arrangement. With a tandem arrangement, the three dimensionality of the flow field appears not to have any lessening effect on the transverse WIV response of cylinders. The spacing ratio at which the tapered cylinder acts more like a single tapered cylinder is noticed to vary from that for the equivalent uniform cylinders in a tandem arrangement. It appears that, because of the three dimensional nature of the wakes downstream of the tapered cylinder, the vortices shed from the upstream tapered cylinder grow weak at much closer distances.

Low Reynolds number flow of power-law fluids over two square cylinders in tandem

The governing partial differential equations have been solved numerically for the 2-D and steady powerlaw fluid flow over two square cylinders in tandem arrangement. Extensive numerical results spanning wide ranges of the governing parameters as Reynolds number (0.1≤Re≤40), power-law index (0.2≤n≤1) and inter-cylinder spacing (2≤L/d≤6) are presented herein; limited results for L/d=24 are also obtained to approach the single cylinder behavior. The detailed flow visualization is done by means of the streamline and vorticity contours in the vicinity of two cylinders. The global characteristics are analyzed in terms of the surface pressure distribution and pressure drag coefficient. The drag coefficient shows the classical inverse dependence on the Reynolds number irrespective of the value of the powerlaw index; the drag on the upstream cylinder is always greater than that for the downstream cylinder.

Re-examination of laminar flow over twin circular cylinders in tandem arrangement

Viscous fluid flow past two identical circular cylinders in a tandem arrangement is numerically investigated at a typical Reynolds number of 200. By considering a large span of spacing ratio (0.1 ⩽ G/D ⩽ 6.0) with a fine interval of 0.1 or less, the dependences on the spacing ratio of the drag force, lift force, lift fluctuation frequency, torque on the cylinder pair and phase difference between the lift fluctuations of the two cylinders are investigated in detail, where D is the diameter of the cylinder and G the surface-to-surface distance between the cylinders. The phase difference between the lift fluctuations of the two cylinders is addressed based on correlation analysis together with the phase diagram, which has received scarce attention before. The phase difference provides further understanding to the dependence of the wake evolutions behind the twin circular cylinders. The numerical investigations show that diverse regimes can be identified according to the dependence of the hydrodynamics on the spacing ratio. The hydrodynamic discontinuities at G/D = 0.9, which have previously been ignored, are reported in this work. The physical correlations between the hydrodynamic discontinuities and the wake patterns are presented.

Numerical Study on Characteristics of Flow and Thermal Fields of Tandem Cylinders

This paper numerically analyzes characteristics of flow and thermal fields of two cylinders in tandem arrangement in the range of the middle Reynolds numbers. The fully implicit forms of continuous equation, unsteady Navier–Stokes (N-S) equations, and energy equation were finite-differenced. The numerical results demonstrate that the flow field has three flow states with the change of the central distance between two cylinders. First, when the central distance between the two circular cylinders is small, the flow in the region between two cylinders remains steady while the flow in the downstream region of the second cylinder has periodic variation vortex. Second, when the central distance increases a little bit more, the whole flow region becomes steady. The third is that when the central distance increases even further, unsteady flow occurs in the whole wake flow field of both first and second cylinders, and vortex shedding can be observed. The reason for the relationship between these three flow states and the central distance of the two circular cylinders is analyzed in detail and is found to be strongly connected to the distribution of the mean velocity.

Application of Potential Theory to Steady Flow Past Two Cylinders in Tandem Arrangement

The wake flow patterns associated with flow past a cylinder and a cylinder-pair in tandem configuration are revisited, compared, and evaluated with respect to the streamline patterns generated based on potential flow theory and superposition of various potential flow elements. The wakes, which are vortex shedding in the lee of the cylinder(s), are reproduced by placing pairs of equal but opposite circulation elements in the potential flow field. The strength of the circulation elements determines the size of the vortices produced. The streamline patterns of flow past a pair of unequal cylinders in tandem configuration provide an indirect means to establish the threshold condition for the wake transition from that of a single bluff body to alternating reattachment behavior. This threshold condition is found to be a function of the diameter ratio,d/D(diametersdandD,d≤D), spacing ratio,L/D(centre-to-centre distance,L, to cylinder diameter,D), and equivalent incident flow speed,U.A unique functional relationshipf(L/D,d/D,U) of this threshold condition is established.

Flow past tandem cylinders under forced vibration

Flow past two cylinders in tandem arrangement under forced vibration has been studied experimentally employing the hydrogen bubble visualization technique. The Reynolds number, based on the cylinder diameter, is fixed at Re=250. In stationary state of the two cylinders with P/D=2.0, dual vortex shedding frequencies fL (St=0.14) and fH (St=0.18) are identified. fL is associated with the shear layer reattachment behavior and fH is related to the single bluff body behavior. Under a variety of forced vibrations of the two cylinders at a fixed vibration amplitude A/D=0.25, diverse and highly-repetitive vortex patterns are yielded. They are classified into two typical modes—a low-frequency mode and a high-frequency mode. The two modes are represented by two vortex patterns yielded from in-phase vibration of the two cylinders with P/D=2.0 and at vibration frequencies fe≈fL and fe≈fH. The difference between the two modes is on the number of vortices formed per vibration cycle. For the low-frequency mode, the number is four; for the high-frequency model, it is two. In both modes, the vortex formation is phase-locked to the cylinder motion. For a specified mode with a fixed vortex number per cycle, the way the vortices evolve in the wake can be somewhat different by changing the vibration frequency, pitch ratio, as well as the vibration type. These affecting factors have been examined in this work, and the associated vortex patterns have been characterized and compared.

Numerical Simulation of Two-Dimensional Flows Using the Feedback Force Immersed Boundary Method

In this paper, numerical simulation of flow around a cylinder using the feedback force immersed boundary method is carried out. The feasibility of algorithm is verified by the numerical simulation of flow past two cylinders in tandem arrangement. The Cartesian adaptive mesh refinement is used in the whole flow field, and the dynamic distribution characteristics of flow field around a single cylinder and double cylinders are obtained when Re=100. Compared with the results in other literatures, the simulation shows a good agreement.