scholarly journals Vibration and Stability of Two Tubes in Cross-Flow

1997 ◽  
Vol 119 (2) ◽  
pp. 142-149 ◽  
Author(s):  
S. Zhu ◽  
S. S. Chen ◽  
Y. Cai
Keyword(s):  
Unsteady Flow ◽  
Flow Velocity ◽  
Water Channel ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Diameter Ratio ◽  
Coupled Vibration ◽  
Fluid Forces ◽  
Stiffness Coefficients ◽  
Fluid Damping

Two tubes in tandem and normal to flow were studied on the basis of the unsteady-flow theory. Motion-dependent fluid forces were measured in a water channel, and the pitch-to-diameter ratio was 1.35. From the measured fluid forces, fluid damping and stiffness were calculated as a function of reduced flow velocity and several Reynolds numbers. Once the fluid-damping and fluid-stiffness coefficients are known, coupled vibration and stability of the two tubes in cross-flow can be predicted.

Fluid Damping and Fluid Stiffness of a Tube Row in Crossflow

1994 ◽  
Vol 116 (4) ◽  
pp. 370-383 ◽  
Author(s):  
S. S. Chen ◽  
S. Zhu ◽  
J. A. Jendrzejczyk
Keyword(s):  
Flow Velocity ◽  
Water Channel ◽  
Excitation Frequency ◽  
Excitation Amplitude ◽  
Design Guideline ◽  
Fluid Forces ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Fluid Damping ◽  
Reliable Design

Motion-dependent fluid forces acting on a tube array were measured as a function of excitation frequency, excitation amplitude, and flow velocity. Fluid-damping and fluid-stiffness coefficients were obtained from measured motion-dependent fluid forces as a function of reduced flow velocity and excitation amplitude. The water channel and test setup provide a sound facility for obtaining key coefficients for fluidelastic instability of tube arrays in crossflow. Once the motion-dependent fluid-force coefficients have been measured, a reliable design guideline, based on the unsteady flow theory, can be developed for fluidelastic instability of tube arrays in crossflow.

Flow Velocity Dependence of Damping in Tube Arrays Subjected to Liquid Cross-Flow

1981 ◽  
Vol 103 (2) ◽  
pp. 130-135 ◽  
Author(s):  
S. S. Chen ◽  
J. A. Jendrzejczyk
Keyword(s):  
Mathematical Modeling ◽  
Flow Velocity ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Elastic Instability ◽  
Velocity Dependence ◽  
Tube Arrays ◽  
Fluid Damping ◽  
Lift And Drag

Experiments are conducted to determine the damping for a tube in tube arrays subjected to liquid cross-flow; damping factors in the lift and drag directions are measured for in-line and staggered arrays. It is found that: 1) fluid damping is not a constant, but a function of flow velocity; 2) damping factors in the lift and drag directions are different; 3) fluid damping depends on the tube location in an array; 4) flow velocity-dependent damping is coupled with vortex shedding process and fluid-elastic instability; and 5) flow velocity-dependent damping may be negative. This study demonstrates that flow velocity-dependent damping is important. These characteristics should be properly taken into account in the mathematical modeling of tube arrays subjected to cross-flow.

The Hydrodynamic Forces Acting on a Long Flexible Circular Cylinder Responding to VIV

2006 ◽  
Author(s):  
P. W. Bearman ◽  
F. J. Huera Huarte ◽  
J. R. Chaplin
Keyword(s):  
Circular Cylinder ◽  
Cross Flow ◽  
Element Model ◽  
Transverse Force ◽  
Diameter Ratio ◽  
Mass Ratio ◽  
Force Coefficients ◽  
Fluid Forces ◽  
Maximum Value ◽  
Vibration Prediction

Distributions of the fluid forces acting along a long flexible circular cylinder free to respond in-line and transverse to a stepped current are presented. Forces are calculated using a finite element model of the cylinder with measured responses providing the input. The length to diameter ratio of the model used was 469, the mass ratio was 3 and the Reynolds number could be varied up to maximum value of approximately 2.6 · 104. Fluid force coefficients for two cases are presented: in the first, the dominant modes are the 2nd cross-flow and the 4th in line. For the second case the leading modes are the 7th and 12th respectively. In general, transverse force coefficients and in-line drag coefficients are found to be larger than those measured for short sections of cylinder undergoing free and forced one and two-dimensional motions. It is anticipated that the results will be of value to developers of vortex-induced vibration prediction methods.

Laboratory Investigation of Helical Strakes With Serrated and Twisted Fins to Suppress VIV

2019 ◽  
Author(s):  
Gustavo R. S. Assi ◽  
Tommaso Crespi
Keyword(s):  
Cross Section ◽  
Water Channel ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Offshore Structures ◽  
Incoming Flow ◽  
Water Currents ◽  
Vortex Induced Vibrations ◽  
Different Types ◽  
Helical Strakes

Abstract Slender offshore structures of a cylindrical cross section, such as drilling and production risers, are susceptible to vortex-induced vibrations (VIV) when exposed to water currents. The present work presents an experimental investigation of the suppression of VIV of a circular cylinder by means of three different types of helical strakes: (i) a strake with continuous blades, (ii) a strake with serrated blades (or fins) and (iii) a strake with serrated blades individually twisted in relation to the incoming flow. By altering the blade geometry to produce the twisted-bladed strake, it was possible to keep the same level of suppression of the cross-flow vibration achieved by conventional strakes, but reducing drag in 15%. Experiments have been conducted in a recirculating water channel at moderate Reynolds numbers.

Motion-Dependent Fluid Force Coefficients for Tube Arrays in Crossflow

2001 ◽  
Vol 123 (4) ◽  
pp. 429-436 ◽  
Author(s):  
S. S. Chen ◽  
G. S. Srikantiah
Keyword(s):  
Excitation Amplitude ◽  
Steam Generators ◽  
Fluid Force ◽  
Force Coefficients ◽  
Fluid Forces ◽  
Stiffness Coefficients ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Fluid Damping ◽  
Series Of Experiments

Fluidelastic instability of tube arrays in crossflow is interesting academically and important in steam generators and heat exchangers. The key elements necessary to accurately predict fluidelastic instability of tube arrays in crossflow are motion-dependent fluid force coefficients. This paper presents several series of experiments that measure motion-dependent fluid forces for various tube arrays. Fluid damping and stiffness coefficients based on the unsteady flow theory were obtained as a function of reduced flow velocity, excitation amplitude, and Reynolds number, and the characteristics of motion-dependent fluid force coefficients were applied to provide some additional insights into fluidelastic instability.

An Experimental Investigation of the Flow Around Straked Cylinders

2007 ◽  
Author(s):  
Ivan Korkischko ◽  
Julio R. Meneghini ◽  
Rafael S. Gioria ◽  
Paulo J. Jabardo ◽  
Enrique Casaprima ◽  
...  
Keyword(s):  
Flow Direction ◽  
Water Channel ◽  
Vortex Formation ◽  
Cross Flow ◽  
Elastic Base ◽  
The Body ◽  
Circular Cylinders ◽  
Air Bearing ◽  
Amplitude Response ◽  
Fluid Forces

This paper presents experimental results concerning the response of circular cylinders with and without strakes. The longitudinal and transverse fluid forces (drag and lift), amplitude response and wake structures of plain and helically straked cylinders are compared. Six different configurations of straked cylinders with pitches (p) equal to 5D, 10D and 15D and heights (h) equal to 0.1D and 0.2D are investigated. Measurements on the dynamic response oscillations of an isolated plain and straked cylinders and flow visualization employing a PIV system are shown. Fixed cylinder drag measurements are also shown. The models are mounted on an elastic base fitted with flexor blades and instrumented with strain gauges or in an air bearing base. The base is fixed on the test-section of a water channel facility. The flexor blades possess a low-damping and the flexor blades base an the air bearing base are free to oscillate only in the cross-flow direction. The Reynolds number of the experiments ranges from 2000 to 10000, and reduced velocities, based on natural frequency in still water, vary up to 13. The drag coefficient is increased by 20% for the h = 0.1D cylinder, and 60% for the h = 0.2D cylinder, comparing both with the plain cylinder. The smaller height strokes (h = 0.1D) do not prevent vortex formation in the region very close to the body, resulting in a decrease of about 50% of the amplitude response compared with the plain cylinder. Lowest amplitude response was found to the p = 10D and h = 0.2D case. The analysis of the vorticity contours shows that the shear layer does not roll close to the body (same result for the other cases with h = 0.2D).

Vortex and Wake Effects on Closely Spaced Marine Risers

2006 ◽  
Author(s):  
G. Germain ◽  
B. Gaurier ◽  
M. Le Boulluec ◽  
E. Fontaine ◽  
J. Capul
Keyword(s):  
Water Channel ◽  
Cross Flow ◽  
Structural Response ◽  
Reynolds Numbers ◽  
Ongoing Research ◽  
Marine Risers ◽  
Steady Current ◽  
Close Proximity ◽  
Wake Effects ◽  
Fluid Interaction

The present paper describes some ongoing research performed for a better understanding of the hydrodynamic loads acting on a riser placed in the wake of an upstream one. Experiments on model tests scaled with real configurations for dual riser interaction in uniform and steady current are presented. A particular attention is paid on how fluid interaction between two cylinders of equal diameter in tandem configuration can significantly modify their structural response in term of amplitude and frequency, compared to that of a single cylinder. The circulation water channel allows to reach Reynolds numbers from 5.5 103 to 5 104. Both in-line and cross-flow responses have been studied and are presented as functions of the reduced velocity. Observations demonstrate that wake effects can be relatively strong. If the dynamic of the upstream cylinder becomes to be well understood, the dynamic of the downstream one is hence much more complex and difficult to predict. When risers become in close proximity due to wake induced oscillations, collisions between cylinders can be observed. Comparisons between experimental and numerical results of the dynamics of a single riser in a flow are also presented.

An Experimental Investigation of the Separation Points on a Circular Rotating Cylinder in Cross Flow

2007 ◽  
Vol 129 (9) ◽  
pp. 1203-1211 ◽  
Author(s):  
L. Labraga ◽  
G. Kahissim ◽  
L. Keirsbulck ◽  
F. Beaubert
Keyword(s):  
Experimental Investigation ◽  
Laser Doppler Anemometry ◽  
Water Channel ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Rotating Cylinder ◽  
Stream Velocity ◽  
Sufficient Information ◽  
Image Velocimetry ◽  
Two Dimensional Flow

The flow past a rotating cylinder placed within a uniform stream is investigated at Reynolds numbers ranging from 8500 to 17,000 to 34,000. The dimensionless rotation rate α (ratio of the cylinder peripheral speed to the free-stream velocity) varies from 0 to 7. The experimental investigation is based on laser-Doppler anemometry measurements and particle-image velocimetry (PIV) within a water channel. The analysis of the experimental results mainly concerns the location of the separation points as defined by various criteria. It is found that the criterion suggested by Moore, Rott and Sears (MRS) is met in the case of the downstream-moving walls. Moreover, this study shows that sufficient information was obtained to confirm that the MRS criterion is still valid even in the case of the upstream-moving walls. This is confirmed by the behavior of the vertical velocity component educed from the averaged two-dimensional flow field obtained by PIV measurements.

A Numerical Study of an Impingement Array Inside a Three Dimensional Turbine Vane

2010 ◽  
Author(s):  
Marcel Leo´n De Paz ◽  
B. A. Jubran
Keyword(s):  
Heat Transfer ◽  
Flow Velocity ◽  
Numerical Study ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Average Deviation ◽  
Turbine Vane ◽  
Cross Flow Velocity ◽  
Target Spacing

A simplified impingement high pressure turbine vane is modeled and solved via Fluent. A relatively flat section of the vane is fitted with 15 0.51mm diameter impingement holes — 5 rows of 3 jets. Results are then compared to known experimental data. Two different turbulence models are used to study this preliminary configuration: K-omega SST and the RNG k-epsilon model. The jet exit Reynolds numbers, cross flow velocity, and the average and local heat transfer distribution are analyzed with varying Reynolds numbers and jet to target spacing. It is observed that the static pressure decreases across the vane with the cross flow velocity increasing towards the trailing edge exit, thereby uniformly increasing the jet exit velocity at each row. Forced convection is seen in the downstream rows in-between span-wise jets due to high cross flow velocities. All numerical results were capable of replicating the higher heat transfer obtained with a higher Reynolds number, and conversely, a lower heat transfer with an increase in jet to target spacing. In its entirety, validating against all correlations, the RNG model obtained an average deviation of 15.7%, while the K-omega SST yielded only 7.8%.

Measurement of the Time Delay Associated With Fluid Damping Controlled Instability in a Normal Triangular Tube Array

2010 ◽  
Author(s):  
John Mahon ◽  
Craig Meskell
Keyword(s):  
Time Delay ◽  
Cross Flow ◽  
Exact Nature ◽  
Fluid Forces ◽  
Fluid Damping ◽  
Order Of Magnitude ◽  
Sample Frequency ◽  
Pitch Ratio ◽  
Parameterized Model ◽  
Semi Empirical

Fluidelastic instability produces large amplitude self-excited vibrations close to the natural frequency of the structure. It is now recognised as the excitation mechanism with the greatest potential for causing damage in tube arrays. It can be split into two mechanisms: fluid stiffness controlled and fluid damping controlled instability. The former is reasonably well understood, although a better understanding for fluid damping controlled instability is required. There is a time delay between tube motion and the resulting fluid forces at the root of fluid damping controlled instability. The exact nature of the time delay is still unclear. The current study directly measures the time delay between tube motion and the resulting fluid forces in a normal triangular tube array with a pitch ratio of 1.32 with air cross-flow. The instrumented cylinder has 36 pressure taps with a diameter of 1 mm, located at the mid-span of the cylinder. The instrumented cylinder was forced to oscillate in the lift direction at four excitation frequencies for a range of flow velocities. Unsteady pressure measurements at a sample frequency of 2kHz were simultaneously acquired along with the tube motion which was monitored using an accelerometer. The instantaneous fluid forces were obtained by integrating the surface pressure data. A time delay between tube motion and resulting fluid forces was obtained. The time delay measured was of the order of magnitude assumed in the semi-empirical models of by Price & Paidoussis (1984, 1986), Weaver and Lever et al. (1982, 1986, 1989, 1993), Granger & Paidoussis (1996), Meskell (2009), i.e. t = μd/U, with μ = O(1). Although, further work is required to provide a parameterized model of the time delay which can be embedded in these models, the data already provides some insight into the physical mechanism responsible.

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