scholarly journals Vortex-induced vibration of a transversely rotating sphere

2018 ◽  
Vol 847 ◽  
pp. 786-820 ◽  
Author(s):  
Methma M. Rajamuni ◽  
Mark C. Thompson ◽  
Kerry Hourigan
Keyword(s):  
Reynolds Number ◽  
Drag Force ◽  
Rotation Rate ◽  
Lift Force ◽  
Oscillation Amplitude ◽  
Fluid Viscosity ◽  
Sphere Diameter ◽  
Force Coefficient ◽  
Vortex Induced Vibration ◽  
Rotation Rates

The effects of transverse rotation on the vortex-induced vibration (VIV) of a sphere in a uniform flow are investigated numerically. The one degree-of-freedom sphere motion is constrained to the cross-stream direction, with the rotation axis orthogonal to flow and vibration directions. For the current simulations, the Reynolds number of the flow, $Re=UD/\unicode[STIX]{x1D708}$, and the mass ratio of the sphere, $m^{\ast }=\unicode[STIX]{x1D70C}_{s}/\unicode[STIX]{x1D70C}_{f}$, were fixed at 300 and 2.865, respectively, while the reduced velocity of the flow was varied over the range $3.5\leqslant U^{\ast }~(\equiv U/(f_{n}D))\leqslant 11$, where, $U$ is the upstream velocity of the flow, $D$ is the sphere diameter, $\unicode[STIX]{x1D708}$ is the fluid viscosity, $f_{n}$ is the system natural frequency and $\unicode[STIX]{x1D70C}_{s}$ and $\unicode[STIX]{x1D70C}_{f}$ are solid and fluid densities, respectively. The effect of sphere rotation on VIV was studied over a wide range of non-dimensional rotation rates: $0\leqslant \unicode[STIX]{x1D6FC}~(\equiv \unicode[STIX]{x1D714}D/(2U))\leqslant 2.5$, with $\unicode[STIX]{x1D714}$ the angular velocity. The flow satisfied the incompressible Navier–Stokes equations while the coupled sphere motion was modelled by a spring–mass–damper system, under zero damping. For zero rotation, the sphere oscillated symmetrically through its initial position with a maximum amplitude of approximately 0.4 diameters. Under forced rotation, it oscillated about a new time-mean position. Rotation also resulted in a decreased oscillation amplitude and a narrowed synchronisation range. VIV was suppressed completely for $\unicode[STIX]{x1D6FC}>1.3$. Within the $U^{\ast }$ synchronisation range for each rotation rate, the drag force coefficient increased while the lift force coefficient decreased from their respective pre-oscillatory values. The increment of the drag force coefficient and the decrement of the lift force coefficient reduced with increasing reduced velocity as well as with increasing rotation rate. In terms of wake dynamics, in the synchronisation range at zero rotation, two equal-strength trails of interlaced hairpin-type vortex loops were formed behind the sphere. Under rotation, the streamwise vorticity trail on the advancing side of the sphere became stronger than the trail in the retreating side, consistent with wake deflection due to the Magnus effect. This symmetry breaking appears to be associated with the reduction in the observed amplitude response and the narrowing of the synchronisation range. In terms of variation with Reynolds number, the sphere oscillation amplitude was found to increase over the range $Re\in [300,1200]$ at $U^{\ast }=6$ for each of $\unicode[STIX]{x1D6FC}=0.15$, 0.75 and 1.5. The VIV response depends strongly on Reynolds number, with predictions indicating that VIV will persist for higher rotation rates at higher Reynolds numbers.

scholarly journals U-shaped fairings suppress vortex-induced vibrations for cylinders in cross-flow

2015 ◽  
Vol 782 ◽  
pp. 300-332 ◽  
Author(s):  
Fangfang Xie ◽  
Yue Yu ◽  
Yiannis Constantinides ◽  
Michael S. Triantafyllou ◽  
George Em Karniadakis
Keyword(s):  
Reynolds Number ◽  
Drag Force ◽  
Three Dimensional ◽  
Cross Flow ◽  
Wake Flow ◽  
Streamwise Vorticity ◽  
Combined System ◽  
Force Coefficient ◽  
Vortex Induced Vibrations ◽  
Adjacent Segments

We employ three-dimensional direct and large-eddy numerical simulations of the vibrations and flow past cylinders fitted with free-to-rotate U-shaped fairings placed in a cross-flow at Reynolds number $100\leqslant \mathit{Re}\leqslant 10\,000$. Such fairings are nearly neutrally buoyant devices fitted along the axis of long circular risers to suppress vortex-induced vibrations (VIVs). We consider three different geometric configurations: a homogeneous fairing, and two configurations (denoted A and AB) involving a gap between adjacent segments. For the latter two cases, we investigate the effect of the gap on the hydrodynamic force coefficients and the translational and rotational motions of the system. For all configurations, as the Reynolds number increases beyond 500, both the lift and drag coefficients decrease. Compared to a plain cylinder, a homogeneous fairing system (no gaps) can help reduce the drag force coefficient by 15 % for reduced velocity $U^{\ast }=4.65$, while a type A gap system can reduce the drag force coefficient by almost 50 % for reduced velocity $U^{\ast }=3.5,4.65,6$, and, correspondingly, the vibration response of the combined system, as well as the fairing rotation amplitude, are substantially reduced. For a homogeneous fairing, the cross-flow amplitude is reduced by about 80 %, whereas for fairings with a gap longer than half a cylinder diameter, VIVs are completely eliminated, resulting in additional reduction in the drag coefficient. We have related such VIV suppression or elimination to the features of the wake flow structure. We find that a gap causes the generation of strong streamwise vorticity in the gap region that interferes destructively with the vorticity generated by the fairings, hence disorganizing the formation of coherent spanwise cortical patterns. We provide visualization of the incoherent wake flow that leads to total elimination of the vibration and rotation of the fairing–cylinder system. Finally, we investigate the effect of the friction coefficient between cylinder and fairing. The effect overall is small, even when the friction coefficients of adjacent segments are different. In some cases the equilibrium positions of the fairings are rotated by a small angle on either side of the centreline, in a symmetry-breaking bifurcation, which depends strongly on Reynolds number.

Full-Scale Reynolds Number VIV Testing of Tri-Helically Grooved Drill Riser Buoyancy Module

2018 ◽  
Author(s):  
Collin Gaskill ◽  
Jie Wu ◽  
Decao Yin
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Hydrodynamic Force ◽  
Oscillation Amplitude ◽  
Cross Flow ◽  
Hydrodynamic Performance ◽  
Test Model ◽  
Force Coefficient ◽  
Test Cylinder ◽  
Test Models

A newly developed Tri-Helically Grooved drilling riser buoyancy module design was tested in the towing tank of SINTEF Ocean in June 2017. This new design aims to reduce riser drag loading and suppress vortex-induced vibrations (VIV). Objectives of the test program were two-fold: to assess the hydrodynamic performance of the design allowing for validation of previous computational fluid dynamics (CFD) studies through empirical measurements, and, to develop a hydrodynamic force coefficient database to be used in numerical simulations to evaluate drilling riser deformation due to drag loading and fatigue lives when subjected to VIV. This paper provides the parameters of the testing program and a discussion of the results from the various testing configurations assessed. Tests were performed using large scale, rigid cylinder test models at Reynolds numbers in the super-critical flow regime, defined as starting at a Reynolds number of Re = 3.5 × 105 – 5.0 × 105 (depending on various literatures) and continuing until Re = 3 × 106. Towing tests, with fixed and freely oscillating test models, were completed with both a bare test cylinder and a test cylinder with the Tri-Helical Groove design. Additional forced motion tests were performed on the helically grooved model to calculate lift and added mass coefficients at various amplitudes and frequencies of oscillation for the generation of a hydrodynamic force coefficient database for VIV prediction software. Significant differences were observed in the hydrodynamic performance of the bare and helically grooved test models considering both in-line (IL) drag and cross-flow (CF) cylinder excitation and oscillation amplitude. For the helically grooved model, measured static drag shows a strong independence from Reynolds number and elimination of the drag crisis region with an average drag coefficient of 0.63. Effective elimination of VIV and subsequent drag amplification was observed at relatively higher reduced velocities, where the bare test model shows a significant dynamic response. A small level of expected response for the helically grooved model was seen across the lower range of reduced velocities. However, disruption of vortex correlation still occurs in this range and non-sinusoidal and highly amplitude-modulated responses were observed.

scholarly journals Calculation of aerodynamic characteristics of flying objects using Prodas and Fluent environments

Mechanik ◽  
2017 ◽  
Vol 90 (7) ◽  
pp. 591-593
Author(s):  
Leszek Baranowski ◽  
Michał Frant
Keyword(s):  
Mach Number ◽  
Experimental Method ◽  
Drag Force ◽  
Lift Force ◽  
Incidence Angle ◽  
Theoretical Method ◽  
Aerodynamic Characteristics ◽  
Pitching Moment ◽  
Force Coefficient ◽  
Moment Coefficient

The article presents the methodology of determining the basic aerodynamic characteristics using the Fluent theoretical method and the theoretical and experimental method using the Prodas program. Presented calculations were made for a 122 mm non-guided missile. In order to compare both methods, the results of calculations of coefficient of drag force, lift force coefficient and pitching moment coefficient as a function of incidence angle of attack and Mach number are shown in graphs.

scholarly journals Vortex-induced vibration of a neutrally buoyant tethered sphere

2013 ◽  
Vol 719 ◽  
pp. 97-128 ◽  
Author(s):  
H. Lee ◽  
K. Hourigan ◽  
M. C. Thompson
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Sphere Diameter ◽  
Circular Orbits ◽  
Neutral Buoyancy ◽  
Number Range ◽  
Vortex Induced Vibration ◽  
Reynolds Number Range ◽  
Neutrally Buoyant ◽  
Planar Symmetry

AbstractA combined numerical and experimental study examining vortex-induced vibration (VIV) of a neutrally buoyant tethered sphere has been undertaken. The study covered the Reynolds-number range $50\leq \mathit{Re}\lesssim 12\hspace{0.167em} 000$, with the numerical ($50\leq \mathit{Re}\leq 800$) and experimental ($370\leqslant \mathit{Re}\lesssim 12\hspace{0.167em} 000$) ranges overlapping. Neutral buoyancy was chosen to eliminate one parameter, i.e. the influence of gravity, on the VIV behaviour, although, of course, the effect of added mass remains. The tether length was also chosen to be sufficiently long so that, to a good approximation, the sphere was constrained to move within a plane. Seven broad but relatively distinct sphere oscillation and wake states could be distinguished. For regime I, the wake is steady and axisymmetric, and it undergoes transition to a steady two-tailed wake in regime II at $\mathit{Re}= 210$. Those regimes are directly analogous to those of a fixed sphere. Once the sphere begins to vibrate at $\mathit{Re}\simeq 270$ in regime III, the wake behaviour is distinct from the fixed-sphere wake. Initially the vibration frequency of the sphere is half the shedding frequency in the wake, with the latter consistent with the fixed-sphere wake frequency. The sphere vibration is not purely periodic but modulated over several base periods. However, at slightly higher Reynolds numbers ($\mathit{Re}\simeq 280$), planar symmetry is broken, and the vibration shifts to the planar normal (or azimuthal) direction, and becomes completely azimuthal at the start of regime IV at $\mathit{Re}= 300$. In comparison, for a fixed sphere, planar symmetry is broken at a much higher Reynolds number of $\mathit{Re}\simeq 375$. Interestingly, planar symmetry returns to the wake for $\mathit{Re}\gt 330$, in regime V, for which the oscillations are again radial, and is maintained until $\mathit{Re}= 450$ or higher. At the same time, the characteristic vortex loops in the wake become symmetrical, i.e. two-sided. For $\mathit{Re}\gt 500$, in regime VI, the trajectory of the sphere becomes irregular, possibly chaotic. That state is maintained over the remaining Reynolds-number range simulated numerically ($\mathit{Re}\leq 800$). Experiments overlapping this Reynolds-number range confirm the amplitude radial oscillations in regime V and the chaotic wandering for regime VI. At still higher Reynolds numbers of $\mathit{Re}\gt 3000$, in regime VII, the trajectories evolve to quasi-circular orbits about the neutral point, with the orbital radius increasing as the Reynolds number is increased. At $\mathit{Re}= 12\hspace{0.167em} 000$, the orbital diameter reaches approximately one sphere diameter. Of interest, this transition sequence is distinct from that for a vertically tethered heavy sphere, which undergoes transition to quasi-circular orbits beyond $\mathit{Re}= 500$.

Movement of a Sphere on a Flat Wall in Non-Newtonian Shear Flow

2017 ◽  
Author(s):  
Yaroslav Ignatenko ◽  
Oleg Bocharov ◽  
Roland May
Keyword(s):  
Shear Flow ◽  
Spherical Particle ◽  
Drag Force ◽  
Newtonian Fluid ◽  
Particle Velocity ◽  
Lift Force ◽  
Fundamental Problem ◽  
Rheological Parameters ◽  
Translational Velocity ◽  
Force Coefficient

For a particle on a wall or cuttings bed in a multiphase flow in confined geometries a condition for onset and lift-off is very important. In this case, a fundamental problem of hydrodynamic forces and torque acting on a particle moving near and on the wall in a viscous fluid needs to be solved. In this paper, systematical simulation of a flow was performed around a perfect rolling or sliding spherical particle near the wall. A shear flow of Newtonian and Herschel-Bulkley fluids was investigated. The simulation was conducted for Reynolds numbers up to 200 and the dimensionless positive particle velocity Vp < 1.4. The relative particle velocity was made dimensionless by dividing it by the incoming flow velocity in front of the particle. The simulation was performed using the open-source CFD package OpenFOAM. The simulation results for Newtonian fluid agree with data presented in the literature. For the particle’s low translational velocity the drag force coefficient in the non-Newtonian fluid is lower than in Newtonian fluid, but for increasing translational velocity the drag force coefficient increases. The lift force coefficient behavior is non-monotonic versus rheology parameters. Lift and drag force show a sudden drop for very small translational velocities. Our simulation shows that in the case of large Bingham numbers the particle’s lift force can be negative for steady perfect particle rolling. Thus, friction between particle and surface prevents particle’s take-off in some cases. Knowing the dependence of the lift force on Reynolds number and rheological parameters allows one to determine incipient motion and take-off conditions for a spherical particle.

Direct numerical simulation of low-Reynolds-number flow past arrays of rotating spheres

2015 ◽  
Vol 765 ◽  
pp. 396-423 ◽  
Author(s):  
Qiang Zhou ◽  
Liang-Shih Fan
Keyword(s):  
Reynolds Number ◽  
Drag Force ◽  
Lift Force ◽  
Immersed Boundary ◽  
Particle Rotation ◽  
Volume Fractions ◽  
Reynolds Number Flow ◽  
Lattice Boltzmann Simulations ◽  
Random Arrays ◽  
Simulation Results

AbstractImmersed boundary-lattice Boltzmann simulations are used to examine the effects of particle rotation, at low particle Reynolds numbers, on flows in ordered and random arrays of mono-disperse spheres. The drag force, the Magnus lift force and the torque on the spheres, are determined at solid volume fractions up to the close-packed limits of the arrays. The rotational Reynolds number based on the angular velocity and the diameter of the spheres is used to characterize the rotational movement of spheres. The results show that the normalized Magnus lift force produced by particle rotation is approximately in direct proportion to the rotational Reynolds number, while the normalized drag force and torque acting on spheres are barely affected by this number. The Magnus lift force is negligible relative to the magnitude of the drag force when the rotational Reynolds number is low. However, it can be very significant, and even larger than the drag force, as the rotational Reynolds number increases up to $O(10^{2})$, especially for low solid volume fractions. Based on the simulation results, relations for the Magnus lift force and the torque for both ordered arrays and random arrays of rotating spheres at solid volume fractions from zero to close-packed limits are formulated. Further, the drag force relations in the literature are revised based on existing theories and the present simulation results for both arrays of spheres.

The Effect of In-Line Oscillation on the Forces of a Cylinder Vibrating in a Steady Flow

2010 ◽  
Author(s):  
Sofia Peppa ◽  
Lambros Kaiktsis ◽  
George Triantafyllou
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Time Dependence ◽  
Vibration Frequency ◽  
Oscillation Frequency ◽  
Lift Force ◽  
Computational Study ◽  
Oscillation Amplitude ◽  
Fluid Forces ◽  
Uniform Stream

In this paper we present a computational study of the forces acting on a circular cylinder vibrating both transversely and in-line to a uniform stream. The in-line vibration frequency is equal to twice the transverse frequency. The cylinder thus follows a figure-eight trajectory, emulating the trajectory of a free vortex-induced vibration. We consider three values of transverse oscillation frequency, in the regime of the natural frequency of the Ka´rma´n street, for a Reynolds number of 400. We find that the fluid forces are greatly influenced by the direction in which the figure-eight is traversed. We also find that the spectrum of the lift force is characterized by the strong presence of odd-numbered higher harmonics. Moreover, depending on the combination of oscillation amplitude and frequency, the lift force exhibits aperiodic time dependence.

Drag Force on a Sphere Moving in Low-Reynolds-Number Pipe Flows

2007 ◽  
Vol 23 (4) ◽  
pp. 423-432 ◽  
Author(s):  
S.-H. Lee ◽  
Tzuyin Wu
Keyword(s):  
Reynolds Number ◽  
Drag Force ◽  
Stokes Equations ◽  
Low Reynolds Number ◽  
Time Derivative ◽  
Creeping Flow ◽  
Navier Stokes ◽  
Sphere Diameter ◽  
Navier Stokes Equations ◽  
Low Reynolds

AbstractIn this paper, the drag force on a sphere moving constantly along the centerline of a circular pipe filled with viscous fluid (the falling-sphere problem) under low Reynolds number condition is investigated via numerical calculation. The incompressible Navier-Stokes equations are formulated in a pseudocompressibility form. The numerical scheme makes use of finite-volume method and the numerical flux terms are evaluated using the Total-Variation Diminishing (TVD) strategy commonly applied to the compressible flow. Steady solution is obtained by marching (iterating) in time until the artificial time derivative of pressure term in the continuity equation drops to zero.In the calculation, six different Reynolds number (Re) ranging from 0.1 to 1 and seven different pipe-to-sphere diameter ratios (D/d) ranging from 5 to 40 are selected to study the pipe-wall effect. In each case, the drag force on the sphere is evaluated and the results are compared with the existing approximate theoretical values derived from correcting the Stokes' formula. Both results agree in trend, but with noticeable deviation in values, particularly for cases with large pipe-to-sphere diameter ratios. The deviation is due to the fact that theoretical values were based on the solution to the linearized Navier-Stokes equations (Stokes' creeping-flow equations), while the fully nonlinear form of the Navier-Stokes equations are adopted in the present calculations. Finally, a least-square regression technique is applied to collapse the calculated results into a single expression exhibiting the functional relationship between the drag force, Reynolds number (Re), and the pipe-to-sphere diameter ratio (D/d).

Study the Influence of Position and the Angle of the Winglets on MITE Micro Air Vehicle

2010 ◽  
Author(s):  
Babak Ganji ◽  
Romina Sadr-Eshkevari
Keyword(s):  
Reynolds Number ◽  
Drag Force ◽  
Lift Force ◽  
Aerodynamic Characteristics ◽  
Flow Solver ◽  
Structured Grid ◽  
Lateral Angle ◽  
Reynolds Number Flow ◽  
Air Vehicle ◽  
Number Flow

In recent years, small aircraft has been thoroughly studied and superior designs have been extensively developed. The aerodynamic design of micro aerial vehicles (MAVs), the most important small aircrafts, in Low-Reynolds number flow (LRNF) has become one of the main concerns to the profession. LRNF is mostly influenced by the airfoil design. Similar to all aircrafts, vertical elevons and winglets play an important role in the aerodynamics of MAVs. On this basis, the present study aimed to assess the effect of lateral angle alterations of the two vertical winglets in the aerodynamics of micro tactical expendable (MITE) in LRNF. A finite element flow solver (FEFS) based on structured grid was employed for studying the aerodynamic characteristics of MITE. The findings of the present study suggest that with the gradual increase in cant angle φ, lift force decreases and drag force remains unchanged. Also with the increase of lateral angle θ, drag force increases significantly and negligible changes are observed in lift force. Vertical elevons play an important role in the control of MITE. Also the effect of Reynolds number on aerodynamic coefficients is discussed.

Parametric Investigation and Mechanism of Low-Drag Fairing Devices for Suppressing Vortex-Induced Vibration

2016 ◽  
Author(s):  
Yun Zhi Law ◽  
Tan Jui Hang Benjamin ◽  
Rajeev K. Jaiman
Keyword(s):  
Reynolds Number ◽  
Drag Reduction ◽  
Drag Force ◽  
Numerical Study ◽  
Flow Direction ◽  
Wake Flow ◽  
Hydrodynamic Performance ◽  
Vortex Induced Vibration ◽  
New Device ◽  
Viv Suppression

It is well known that fairing devices are better alternatives than helical strakes due to their low-drag performance while suppressing vortex-induced vibration (VIV). Our objective is to present a systematic numerical study to understand the hydrodynamic performance and physical mechanism of fairing configurations and then propose a new device for suppressing VIV and reducing drag force. In this work, we simplify our investigation by allowing the cylinder-fairing system to oscillate in cross-flow direction without rotation. Firstly, we present a set of simulations of vortex-induced vibration for Short Crab Claw (SCC) fairings [1] with different nondimensional length (Lf/D), where Lf is the length of fairing and D denotes the diameter of cylinder. To establish the relation between the length of fairing and the performance with respect to VIV suppression and drag reduction, we consider the length ratio Lf/D = 1.25, 1.50, 2.00. The underlying VIV suppression mechanism is investigated with the aid of force and amplitude variations, wake flow structures and frequency ratios. Our results show that the SCC fairing with longer length performs better by suppressing the amplitude up to 84% and reduces the drag coefficient by 40%. This finding implies that by offsetting the vortices shed away from the main cylinder, it lowers the influence of vortex interactions, which leads to the suppression of VIV and net reduction in the drag force generation. Based on this mechanism, we propose a new design of fairing, namely the “Hinged C-shaped”, which consists of a thin splitter plate (connected at the base of main cylinder) bifurcating into a C-shaped geometry after a certain distance. Through our numerical study on its hydrodynamic performance, it is shown to be efficient with respect to VIV suppression and drag reduction. To understand the VIV suppression physics, the numerical study is conducted in two-dimension for the cylinder-fairing mounted elastically with mass ratio m* = 2.6 and the damping ξ = 0.001 at low Reynolds number. We further demonstrate the performance of the new fairing device in three-dimension at sub-critical Reynolds number.

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