Attached Splitter Plate Research Articles

Effects of splitter plate and mass ratio on flow-induced vibration and heat transfer characteristics of a circular cylinder in turbulent flow: A numerical study

The two-degree-of-freedom (2DOF) flow-induced vibration (FIV) of a circular cylinder with heat transfer in turbulent flow is numerically investigated. The cylinder with an attached splitter plate is elastically supported and allowed to vibrate in both in-line and transverse directions. The unsteady RANS and energy equations along with the SST k-ω turbulent model are coupled with the equation of vibration to study the FIV of the cylinder. The effects of the attached plate length (L/D = 0.5, 1.0, and 1.5) and the mass ratio (mr=2 and 6.76) on the heat transfer rate, vortex shedding patterns, vibration trajectories, FFT, and cylinder displacements are studied in a wide range of Reynolds number (1156–9246) and reduced velocity (2–16). The results indicate that FIV can have either a positive or negative effect on heat transfer enhancement, depending on the splitter plate length and the type of cylinder vibration response. At high Reynolds numbers, the cylinder vibration response is observed in the galloping region, accompanied by a significant vibration amplitude. In this region, for L = 0.5D, vibration has a positive effect on heat transfer, while for other lengths, this effect is negative. For L = 1.5D and a reduced velocity of 5.5, contributions of vortex-induced vibration (VIV) and surface area in the heat transfer enhancement are 23.5 % and 44.3 %, respectively. By reducing the mass ratio from 6.76 to 2.6 for L = 0.5D, the heat transfer rate increases by approximately 40 % compared to a stationary cylinder.

Laminar flow-induced vibration of a three-degree-of-freedom circular cylinder with an attached splitter plate

Splitter plates are widely used for drag reduction and vibration control or enhancement of circular cylinders. The effects of a splitter plate on the vertical flow-induced vibrations of a circular cylinder have been well studied. However, its effects on the vertical-torsional coupled vibrations require further investigation. In this paper, the three-degree-of-freedom (TDoF) flow-induced vibrations of a circular cylinder with an attached splitter plate are numerically investigated at a Reynolds number of 100. The ratio between the torsional and vertical natural frequencies is varied within fθ,0/fh,0 = 6, 4, 3, 2, and 1. Numerical results show that the flow-induced vibrations of a TDoF cylinder-plate assembly, depending on the frequency ratio, may differ significantly from those of a single-degree-of-freedom (SDoF) vertical or torsional assembly. For cylinder-plate assemblies with fθ,0/fh,0 = 6–2, the vibrations can be divided into a vertical vibration-dominated branch (V branch), a torsional vibration-dominated branch (T branch), and a coupled vibration-dominated branch (C branch). The V branch vibration of a TDoF assembly is similar to that of an SDoF vertical assembly at the same reduced flow velocity, while the difference increases with decreasing the frequency ratio. The T branch vibration of a TDoF assembly is almost identical to the vibration of an SDoF torsional assembly at the same reduced flow velocity. The ratio between the torsional and vertical vibration amplitudes increases with decreasing the frequency ratio in the C branch. For the assembly with fθ,0/fh,0 = 1, vertical-torsional coupled vortex-induced vibrations are observed with the largest torsional amplitude as high as 46.3°. The vibrations of TDoF assemblies with all considered frequency ratios may be more severe than those of SDoF vertical and torsional assemblies within specific ranges of reduced flow velocities. The mean drag coefficients for the fθ,0/fh,0 = 6–2 assemblies are lower than a stationary circular cylinder but often higher than a stationary cylinder-plate assembly. The mean drag coefficients for the fθ,0/fh,0 = 1 assembly in the lock-in range are considerably larger than that of a stationary circular cylinder. For TDoF assemblies with fθ,0/fh,0 = 6–2, the V branch and C branch vibrations are mainly driven by the interaction between the assembly and the shear layers, while the T branch vibrations are excited by the typical 2S mode of vortex shedding. The 2S vortex shedding mode is also observed in the lock-in range of the fθ,0/fh,0 = 1 assembly.

Flow Characteristics and Fluid Forces Reduction of Flow Past Two Tandem Cylinders in Presence of Attached Splitter Plate

Numerical simulations are carried out to study the flow around two tandem square cylinders (SC) under the effect of spacing ratio(g/D) and splitter plate length (l/D) for a fixed Reynolds number (Re) = 100. The g/D is varied from 0 to 10 and l/D is varied from 0.5 to 10. The splitter plate length is found to have strong effect on vortex shedding and fluid forces. The maximum reduction in mean drag coefficient is observed at l/D = 8, that is 15% and 78% for upstream and downstream cylinders, respectively. The maximum reduction in root-mean-square value of lift coefficient is found at l/D = 10, that is 99%. The flow pattern at both of these points is steady flow. There is 100% vortex shedding suppression for l/D > 5. The observed flow patterns for flow past tandem cylinders without splitter plate are; single bluff body (SBB), steady flow (SF), quasi-steady flow (QSF), fully developed flow (FDF) and fully developed two-row vortex street flow (FDTRVS) regimes. SBB, QSF and SF regimes were observed in presence of splitter plate.

Flow-induced vibration of two tandemly arranged circular cylinders with attached splitter plates

In this numerical study, vortex-induced vibrations (VIVs) of two elastically mounted tandem circular cylinders with attached splitter plate are simulated at Re=150, mr=2 and damping ratio of ζ = 0. The cylinders are allowed to vibrate in both streamwise and transverse directions. Three different configurations including splitter plate attached to only upstream cylinder, attached to only downstream cylinder and attached to both cylinders are investigated. Results show that in many of the examined cases the galloping response occurs which led to large values of vibration amplitudes. Moreover, in tandem cylinders with a large spacing ratio, adding a plate to the downstream cylinder does not change the vibrations of the upstream cylinder at small to medium reduced velocities. For this case, the galloping vibration occurs at medium reduced velocities for downstream cylinder-plate assembly (CP) and at high reduced velocity for downstream cylinder. Furthermore, adding a plate to the upstream cylinder greatly affects the vibrations of both cylinders, causing the galloping vibration of the upstream cylinder at low reduced velocity and the galloping vibration of upstream CP at medium reduced velocity. During the galloping response, various wake patterns behind downstream cylinder-plate body including P + S, 2P, 2D, T + P, 2T, Q + T and 2Q are observed.

Torsional vibration of a circular cylinder with an attached splitter plate in laminar flow

Splitter plates have been recognized as useful passive devices to reduce drag, mitigate flow-induced vibration, and enhance heat transfer efficiency of a circular cylinder. However, undesired torsional flow-induced vibrations due to splitter plate attachment require further investigation. This paper numerically studies the flow-induced torsional vibrations of an elastically mounted circular cylinder with an attached splitter plate in laminar flow with a Reynolds number of 100. A finite volume formulation is utilized to solve the incompressible two-dimensional fluid governing equations. Torsional vortex-induced vibrations (VIVs) are observed at lower reduced flow velocities, while a symmetry-breaking bifurcation occurs as the reduced flow velocity increases, after which the cylinder-plate assembly vibrates around a nonzero equilibrium angle. The numerical results show that the synchronization range of VIV extends, the peak VIV amplitude increases, and the critical reduced flow velocity for the bifurcation decreases with decreasing the moment of inertia. The symmetry-breaking bifurcation is due to a combined effect of the structural restoring moment and the flow-induced moment. The critical reduced velocity of the bifurcation and the nonzero equilibrium angle at any reduced velocity can be calculated based on the mean moment coefficients of the cylinder-plate assembly. The flow-induced moment is mainly induced by the pressure difference between the splitter plate's upper and lower surfaces. The phase difference between the torsional moment and displacement is 0° at lower reduced velocities, while the phase difference jumps to 180° at a reduced velocity of approximately 6.5. The mean drag coefficient of the vibrating cylinder-plate assembly is lower than the mean drag coefficient of a stationary circular cylinder but often higher than that of a stationary cylinder-plate assembly. The dominant frequency of the drag force is twice the vibration frequency before the symmetry-breaking bifurcation, while the dominant frequency becomes consistent with the vibration frequency after the bifurcation. The typical 2S mode of vortex shedding is identified for all considered moments of inertia and reduced flow velocities. However, the timing of a non-shedding vortex changes at the critical flow velocities for the phase jump and symmetry-breaking bifurcation. The observed torsional vibrations suggest that circular cylinders with splitter plate attachments may be competitive candidates for VIV-based energy harvesting, while they may not be good choices for heat exchangers.

On the linear global stability analysis of rigid-body motion fluid–structure-interaction problems

Abstract

Dynamics of a circular cylinder with an attached splitter plate in laminar flow: A transition from vortex-induced vibration to galloping

Flow-induced vibration (FIV) of a circular cylinder with an attached splitter plate in a laminar flow with Re = 100 is studied numerically. First, the mechanical model along with mathematical formulations is proposed to describe the fluid-structure interaction (FSI) between the elastically supported cylinder–plate body and the surrounding flow. Subsequently, an FSI solution procedure is developed based on the characteristic-based split finite element method, and its accuracy and stability are validated using vortex-induced vibrations (VIVs) of a plain circular cylinder with benchmark solutions. Finally, using FSI simulations, effects of the plate length (L), reduced velocity, mass ratio and damping coefficient on the dynamic response, fluid load, and flow pattern of the cylinder–plate assembly are investigated in detail. As the plate length increases from L/D = 0–1.5 (D is the cylinder diameter), three FIV modes are observed successively: VIV, coupled VIV and galloping, and separated VIV and galloping, along with three vortex modes in the wake: 2S (two separated vortices in one cycle), P+S (a vortex pair and a separated vortex in one cycle), and 2P (two vortex pairs in one cycle). Moreover, it is found that the lift components generated from the splitter plate and the cylinder behave, respectively, as the driving force and the suppressing force of galloping, and the transition from VIV to galloping can be taken as a result of the competition between them. The cylinder–plate model presented could be taken as a benchmark model demonstrating the VIV-galloping interaction and applied to the design of novel FSI-based energy harvesters.

Numerical study of flow-induced vibration of a circular cylinder with attached flexible splitter plate at low

Flow-induced vibration (FIV) of an elastically mounted circular cylinder with an attached splitter plate in uniform flow is studied numerically via a stabilized space–time finite element method. The Reynolds number based on the cylinder diameter $D$ and the free-stream speed is restricted to 150. The ratio of the density of the body to that of the fluid, for the major part of the study, is 10. Two different reduced speeds are defined to quantify the compliance of the elastic support and flexibility of the splitter plate, respectively: $U_{s}^{\ast }$ based on the natural frequency of the spring–mass system and $U_{p}^{\ast }$ based on the fundamental natural frequency of the plate. Flow past a stationary cylinder ($U_{s}^{\ast }=0$) with a flexible splitter plate of length $3.5D$ is studied at different values of $U_{p}^{\ast }$. The vibration response of the plate exhibits lock-in with various eigenmodes of the plate in different ranges of $U_{p}^{\ast }$. The onsets of these lock-in regions are abrupt and hysteretic. The elastically mounted cylinder, without the splitter plate, undergoes large-amplitude vortex-induced vibration (VIV) for $4<U_{s}^{\ast }<7$. These large-amplitude oscillations are a consequence of synchronization, wherein the vortex shedding frequency locks in to the cylinder oscillation frequency. A rigid splitter plate attached to the cylinder reduces significantly the peak amplitude during VIV. Increasing the length of the plate from $1.5D$ to $3.5D$ only marginally affects the peak amplitude. It, however, leads to a wider range of lock-in. Unlike the case of an isolated cylinder, the lock-in and desynchronization regimes are not well demarcated in the presence of the splitter plate. Further, galloping is observed beyond a critical value of $U_{s}^{\ast }$; the amplitude of vibration increases with an increase in $U_{s}^{\ast }$ while the vibration frequency is relatively low and remains nearly constant. Increase in plate length delays, in terms of $U_{s}^{\ast }$, the onset of galloping. It is also found that the flexibility of the plate affects the maximum oscillation amplitude in the VIV regime. It also dictates the presence/absence of galloping. The system behaves similar to an isolated cylinder for a very flexible plate. The response is devoid of galloping, but relatively large amplitude of oscillation is observed during lock-in. The behaviour of the cylinder with a stiff plate is similar to that with the rigid one. The galloping instability sets in when the flexibility of the plate is less than a certain value ($U_{p}^{\ast }<4.7$, approximately for $U_{s}^{\ast }=22$). The VIV and galloping are separated by a range of $U_{s}^{\ast }$ in which the flow is either steady, for longer plates, or exhibits very weak vortex shedding. In the VIV regime, the plate tip and cylinder vibrate in phase for low $U_{p}^{\ast }$; their motion is out of phase for larger $U_{p}^{\ast }$. The change in phase is also associated with change in the frequency of vibration. At low $U_{p}^{\ast }$, the frequency of vibration is close to the first natural frequency of the system, while at high $U_{p}^{\ast }$ it becomes closer to the second natural frequency. The vibration amplitude of the cylinder is close to maximum in the VIV regime for $U_{s}^{\ast }=6$. Computations for various $U_{p}^{\ast }$, for $U_{s}^{\ast }=6$ and $22$, are utilized to determine optimal flexibility that leads to minimal FIV. The effect of the length of the flexible splitter plate, mass ratio and damping ratio is studied. A strategy is proposed to utilize the computations from various combinations of $U_{s}^{\ast }$ and $U_{p}^{\ast }$ to choose the appropriate flexibility of the attached splitter plate to minimize FIV.

Numerical study on flow over a confined oscillating cylinder with a splitter plate

PurposeThis study aims to investigate the effect of the simultaneous usage of active and passive methods (which in this case are rotational oscillation and attached splitter plate, respectively) on the flow and temperature fields to find an optimum situation which this combination results in heat transfer increment and drag reduction.Design/methodology/approachThe method of the solution was based on finite volume discretization of Navier–Stokes equations. A dynamic grid is coupled with the solver by the arbitrary Lagrangian–Eulerian (ALE) formulation for modeling cylinder oscillation. Parametric studies were performed by altering oscillation frequency, splitter plate length and Reynolds number.FindingsOscillation in different frequencies was found to be complicated. Higher frequencies provide more heat transfer, but in the lock-on region, they bring remarkable increment to the drag coefficient. It was observed that simultaneous usage of oscillation and splitter plate may have both positive and negative effects on drag reduction and heat transfer increment. Finally F = 2 and L = 0.5 were chosen as an optimum combination.Originality/valueIn this study, the laminar incompressible flow and heat transfer from a confined rotationally oscillating circular cylinder with an attached splitter plate are investigated. Parametric studies are performed by changing oscillation frequency, splitter plate length and Reynolds number.

Experimental investigation of flow over a square cylinder with an attached splitter plate at intermediate reynolds number

The present work is an experimental investigation of flow control over a square cylinder using an attached splitter plate. The experiments are mainly conducted at a Reynolds number of 485. A splitter plate of varying length from 0 to 6 times of the cylinder width is attached to the rear side of the square cylinder to control the flow. The thickness of the splitter plate is kept constant at 10% of cylinder width. The flow interference of a square cylinder with an attached splitter plate is observed using PIV, Hot wire and flow visualization techniques. The primary focus is given on the flow structure and related forces. From the experiments, it has been observed that a secondary vortex appears at the tail edge of the plate after a particular length of the splitter plate. This vortex rotation is opposite to the main vortex and it influences the primary vortex shedding as well as shear layer formation. As a result, the plate modifies the wake size and flow structure behind the cylinder. The drag coefficient and the Strouhal number decrease with an increase in splitter plate length. A correlation is found between the splitter plate length, Reynolds number, and the drag coefficient. The effect of the splitter plate length on the flow field is also studied in terms of velocity, vorticity, streamlines, recirculation length, and turbulence statistics.

Effect of arrangement of inline splitter plate on flow past square cylinder

Two-dimensional numerical study has been carried out to investigate the effect of the presence of a single splitter plate in upstream location, and presence of two splitter plates, in upstream as well as downstream locations, for low Reynolds number incompressible flow past a square cylinder. Using finite difference discretisation and MAC algorithm, an indigenously developed computational code has been used for solution of the governing flow equations. The length of the plate and its position do play good role in controlling the flow past the cylinder. The difficulty lies in identifying an optimum configuration of these parameters. The length of the attached splitter plate as well as separation of the detached splitter plate of fixed length are varied for both the upstream and downstream configurations up to maximum Reynolds number of 200. To begin with, the effect of upstream splitter plate alone in attached as well as detached configuration is studied with an aim to identify the optimum configuration associated with reduced drag as well as delayed onset of vortex shedding. Then, for the optimum configuration of the upstream plate, the effect of downstream plate on flow characteristics and critical Reynolds number for onset of vortex shedding has been studied.

Flow around fishlike shapes studied using multiparticle collision dynamics

Empirical measurements of hydrodynamics of swimming fish are very difficult. Therefore, modeling studies may be of great benefit. Here, we investigate the suitability for such a study of a recently developed mesoscale method, namely, multiparticle collision dynamics. As a first step, we confine ourselves to investigations at intermediate Reynolds numbers of objects that are stiff. Due to the lack of empirical data on the hydrodynamics of stiff fishlike shapes we use a previously published numerical simulation of the shapes of a fish and a tadpole for comparison. Because the shape of a tadpole resembles that of a circle with an attached splitter plate, we exploit the knowledge on hydrodynamic consequences of such an attachment to test the model further and study the effects of splitter plates for objects of several shapes at several Reynolds numbers. Further, we measure the angles of separation of flow around a circular cylinder and make small adjustments to the boundary condition and the method to drive the flow. Our results correspond with empirical data and with results from other models.

Control of Vortex Shedding of Circular Cylinder in Shallow Water Flow Using an Attached Splitter Plate

In the present work, passive control of vortex shedding behind a circular cylinder by splitter plates of various lengths attached on the cylinder base is experimentally investigated in shallow water flow. Detailed measurements of instantaneous and time-averaged flow data of wake flow region at a Reynolds number of Re=6300 were obtained by particle image velocimetry technique. The length of the splitter plate was varied from L∕D=0.2 to L∕D=2.4 in order to see the effect of the splitter plate length on the flow characteristics. Instantaneous and time-averaged flow data clearly indicate that the length of the splitter plate has a substantial effect on the flow characteristics. The flow characteristics in the wake region of the circular cylinder sharply change up to the splitter plate length of L∕D=1.0. Above this plate length, small changes occur in the flow characteristics.

Supercritical Reynolds number experiments on a freely rotatable cylinder/splitter plate body

The behavior of a circular cylinder with attached splitter plate, under conditions where the entire cylinder/splitter plate body was free to rotate about the cylinder axis, has been studied experimentally as Reynolds number was increased through the critical value (laminar boundary layer separation replaced by turbulent boundary layer separation farther downstream). As in previous experiments (at lower Reynolds numbers), it was found that the plate did not align itself with the free stream, but instead rotated to some off-axis equilibrium angle, θ. For plates with splitter plate length, L, less than one cylinder diameter, D, θ dropped very quickly to some minimum value in the transitional Reynolds number range, then slowly increased toward some new supercritical value, which in all cases was smaller than that in the subcritical range. For cases with L/D≳1, however, in the transitional Reynolds number range, the splitter plate overshot the centerline and commenced oscillating between extremes on either side. At supercritical Reynolds numbers, for cases with L/D≤2, a new equilibrium angle eventually reestablished itself on one side or the other; but for cases with L/D≥2.5, the cylinder/splitter plate body continued to oscillate between extremes on either side, even at the highest Reynolds numbers tested.