Galloping 2D Tests of a Two Cylinder Bundle

2007 ◽  
Author(s):  
Henning Braaten ◽  
Halvor Lie ◽  
Martin So̸reide ◽  
Stian Svardal
Keyword(s):  
Cross Sections ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Cross Flow ◽  
Present System ◽  
Velocity Range ◽  
Fluid Forces ◽  
Sea Bottom ◽  
Flow Induced Vibrations ◽  
Torsion Stiffness

Elastic mounted noncircular cross section geometries can produce large displacements and/or rotations often denoted galloping or fluttering, see e.g. Blevins (1990) and Faltinsen (1990). For such a structure the fluid forces that act on the structure change with orientation to the flow. If the oscillating fluid force tends to increase vibration, the structure is dynamically unstable and very large-amplitude vibration, galloping, can result. Statoil ASA has commissioned a model test campaign at MARINTEK to study the behaviour of flow induced vibrations for a 2D model of two pipes tied together with a special emphasize on the possibility of galloping response. The results were used in a Statoil study on the behaviour of free-span pipelines near sea bottom. However, the test results are generic and can also be relevant for deep water risers and umbilicals. The short rigid pipe section model was elastically mounted and was free to move as a single degree of freedom (SDOF) in the cross-flow direction. In some tests it was also allowed to rotate around the cylinders axial axis (2-DOF). By adjusting the torsion stiffness the same natural frequencies in the two DOFs were obtained. The cylinder was constrained in in-line direction. The tests were done for several different headings and towing velocities. Altogether 189 towing tests were done. As key result relative large displacement-to-diameter ratios were observed in the reduced velocities range 1–20. By evaluation of the oscillating frequency the response was characterized. For the lower reduced velocity range (say up to 10) the response could easily be characterized as VIV and for the highest reduced velocities as galloping. In an intermediate reduced velocity range a mixed kind of behavior is observed. These results coincide with results reported of flow induced vibrations of bridge decks with rectangular cross-sections, confer Blevins (1990). Most galloping analysis utilizes quasi-steady fluid assumption. A fundamental assumption for the quasi-steady assumption is that the fluid forces are quasi-steady and the structure oscillates around its natural frequency. Oscillating vortex shedding forces are at much higher frequencies and do not matter in the galloping response. Since the galloping response frequencies overlap with the vortex-shedding frequency it was concluded that the quasi-steady fluid assumption is not applicable for the present system.

Interference in a three-dimensional array of jets

2015 ◽  
Vol 26 (5) ◽  
pp. 795-819
Author(s):  
P. E. WESTWOOD ◽  
F. T. SMITH
Keyword(s):  
Cross Sections ◽  
Flow Direction ◽  
Three Dimensional ◽  
Cross Flow ◽  
Longitudinal Vortex ◽  
Cross Sectional ◽  
Dimensional Array ◽  
Unsteady Jets ◽  
The Cross ◽  
Jet Cross Sections

The theoretical investigation here of a three-dimensional array of jets of fluid (air guns) and their interference is motivated by applications to the food sorting industry especially. Three-dimensional motion without symmetry is addressed for arbitrary jet cross-sections and incident velocity profiles. Asymptotic analysis based on the comparatively long axial length scale of the configuration leads to a reduced longitudinal vortex system providing a slender flow model for the complete array response. Analytical and numerical studies, along with comparisons and asymptotic limits or checks, are presented for various cross-sectional shapes of nozzle and velocity inputs. The influences of swirl and of unsteady jets are examined. Substantial cross-flows are found to occur due to the interference. The flow solution is non-periodic in the cross-plane even if the nozzle array itself is periodic. The analysis shows that in general the bulk of the three-dimensional motion can be described simply in a cross-plane problem but the induced flow in the cross-plane is sensitively controlled by edge effects and incident conditions, a feature which applies to any of the array configurations examined. Interference readily alters the cross-flow direction and misdirects the jets. Design considerations centre on target positioning and jet swirling.

scholarly journals Flow-induced vibrations of a rotating cylinder

2014 ◽  
Vol 740 ◽  
pp. 342-380 ◽  
Author(s):  
Rémi Bourguet ◽  
David Lo Jacono
Keyword(s):  
Symmetry Breaking ◽  
Flow Direction ◽  
Cross Flow ◽  
Maximum Amplitude ◽  
Rotating Cylinder ◽  
Free Vibrations ◽  
Cylinder Surface ◽  
Single Vortex ◽  
Flow Induced Vibrations ◽  
The Impact

AbstractThe flow-induced vibrations of a circular cylinder, free to oscillate in the cross-flow direction and subjected to a forced rotation about its axis, are analysed by means of two- and three-dimensional numerical simulations. The impact of the symmetry breaking caused by the forced rotation on the vortex-induced vibration (VIV) mechanisms is investigated for a Reynolds number equal to $100$, based on the cylinder diameter and inflow velocity. The cylinder is found to oscillate freely up to a rotation rate (ratio between the cylinder surface and inflow velocities) close to $4$. Under forced rotation, the vibration amplitude exhibits a bell-shaped evolution as a function of the reduced velocity (inverse of the oscillator natural frequency) and reaches $1.9$ diameters, i.e. three times the maximum amplitude in the non-rotating case. The free vibrations of the rotating cylinder occur under a condition of wake–body synchronization similar to the lock-in condition driving non-rotating cylinder VIV. The largest vibration amplitudes are associated with a novel asymmetric wake pattern composed of a triplet of vortices and a single vortex shed per cycle, the ${\rm T} + {\rm S}$ pattern. In the low-frequency vibration regime, the flow exhibits another new topology, the U pattern, characterized by a transverse undulation of the spanwise vorticity layers without vortex detachment; consequently, free oscillations of the rotating cylinder may also develop in the absence of vortex shedding. The symmetry breaking due to the rotation is shown to directly impact the selection of the higher harmonics appearing in the fluid force spectra. The rotation also influences the mechanism of phasing between the force and the structural response.

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).

scholarly journals Flow-Induced Vibrations of Single and Multiple Heated Circular Cylinders: A Review

Energies ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 8496
Author(s):  
Ussama Ali ◽  
Md. Islam ◽  
Isam Janajreh ◽  
Yap Fatt ◽  
Md. Mahbub Alam
Keyword(s):  
Heat Transfer ◽  
Vortex Shedding ◽  
Heat Exchangers ◽  
Power Plants ◽  
Bluff Body ◽  
The Body ◽  
Circular Cylinders ◽  
Fluid Forces ◽  
Spacing Ratio ◽  
Flow Induced Vibrations

This study is an effort to encapsulate the fundamentals and major findings in the area of fluid-solid interaction, particularly the flow-induced vibrations (FIV). Periodic flow separation and vortex shedding stretching downstream induce dynamic fluid forces on the bluff body and results in oscillatory motion of the body. The motion is generally referred to as flow-induced vibrations. FIV is a dynamic phenomenon as the motion, or the vibration of the body is subjected to the continuously changing fluid forces. Sometimes FIV is modeled as forced vibrations to mimic the vibration response due to the fluid forces. FIV is a deep concern of engineers for the design of modern heat exchangers, particularly the shell-and-tube type, as it is the major cause for the tube failures. Effect of important parameters such as Reynolds number, spacing ratio, damping coefficient, mass ratio and reduced velocity on the vibration characteristics (such as Strouhal number, vortex shedding, vibration frequency and amplitude, etc.) is summarized. Flow over a bluff body with wakes developed has been studied widely in the past decades. Several review articles are available in the literature on the area of vortex shedding and FIV. None of them, however, discusses the cases of FIV with heat transfer. In particular systems, FIV is often coupled to heat transfer, e.g., in nuclear power plants, FIV causes wear and tear to heat exchangers, which can eventually lead to catastrophic failure. As the circular shape is the most common shape for tubes and pipes encountered in practice, this review will only focus on the FIV of circular cylinders. In this attempt, FIV of single and multiple cylinders in staggered arrangement, including tandem and side-by-side arrangement is summarized for heated and unheated cylinder(s) in the one- and two-degree of freedom. The review also synthesizes the effect of fouling on heat transfer and flow characteristics. Finally, research prospects for heated circular cylinders are also stated.

Flow Induced Oscillation of a Set-In Circular Cylinder

2009 ◽  
Author(s):  
F. Oviedo-Tolentino ◽  
R. Romero-Mendez ◽  
A. Hernandez-Guerrero ◽  
J. M. Luna
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Flow Behavior ◽  
Cross Flow ◽  
Close Relation ◽  
Structure Interaction ◽  
Visualization Techniques ◽  
Flow Experiments

This work studies the fluid-structure interaction of a set-in, large aspect-ratio circular cylinder in cantilever subjected to a cross flow. Experiments were conducted in a water tunnel and observations were obtained using flow visualization techniques and direct observation of the deflection of the cylinder. The flow behavior was observed using dye injection. The experiments show that the dominant vibration of the cylinder is transversal to the flow direction, and that the first mode of vibration of the cylinder appears at a particular Reynolds number, which is a function of the mechanical properties of the cylinder. The deflection stops when the Reynolds number is increased. The peak deflection and frequency of oscillation, as a function of the Reynolds number, were also determined. The analysis shows a close relation between the frequency of oscillation and the frequency of appearance of a vortex shedding. For large deflections of the cylinder the flow structure is modified substantially, and the frequency at which vortex appears is different to the frequency that occurs for fixed cylinders.

Experimental Investigation of Flow-Induced Vibrations Interference Between Two Circular Cylinders in Tandem Arrangements

2005 ◽  
Author(s):  
Gustavo R. S. A´ssi ◽  
Julio R. Meneghini ◽  
Jose´ A. P. Aranha ◽  
Peter W. Bearman ◽  
Bruno S. Carmo ◽  
...  
Keyword(s):  
Flow Direction ◽  
Water Channel ◽  
Cross Flow ◽  
Elastic Base ◽  
Circular Cylinders ◽  
Interference Phenomenon ◽  
Flow Induced Vibrations ◽  
Set Up ◽  
Flow Interference ◽  
Future Work

This paper presents experimental results concerning flow-induced oscillations of rigid-circular cylinders in tandem. Preliminary results are presented: new measurements on the dynamic response oscillations of an isolated cylinder and flow interference of two cylinders in tandem are shown. The oscillations are due to vortex-induced vibrations (VIV). Models are mounted on an elastic base fitted with flexor blades and instrumented with strain gages. The base is fixed on the test section of a water channel facility. The flexor blades possess a low damping characteristic [ζ ≈ 0.008 and less] and they are free to oscillate only in the cross-flow direction. The Reynolds number of the experiments is from 3,000 to 13,000 and reduced velocities, based on natural frequency in still water, range up to 12. The interference phenomenon on flow-induced vibrations can be investigated by conducting experiments in two ways: first, the upstream cylinder is maintained fixed and the downstream one is mounted on the elastic base; subsequently, an investigation will be carried out letting both cylinders oscillate transversally. The results for an isolated cylinder are in accordance with other measurements in the literature for m* ≈ 2 and m* ≈ 8. For the tandem arrangement (m* ≈ 2), the trailing cylinder oscillation presents what previous researchers have termed interference galloping behaviour for a centre-to-centre gap spacing ranging from 3·0D to 5·6D. These initial results validate the experimental set up and lead the way for future work; including tandem, staggered and side-by-side arrangements with the two cylinders free to move.

scholarly journals Vortex-induced vibration and galloping of prisms with triangular cross-sections

2017 ◽  
Vol 817 ◽  
pp. 590-618 ◽  
Author(s):  
Banafsheh Seyed-Aghazadeh ◽  
Daniel W. Carlson ◽  
Yahya Modarres-Sadeghi
Keyword(s):  
Natural Frequency ◽  
Cross Sections ◽  
Flow Direction ◽  
Cross Flow ◽  
Low Frequency ◽  
Limited Range ◽  
Triangular Prism ◽  
Vortex Induced Vibration ◽  
Lock In ◽  
Type Response

Flow-induced oscillations of a flexibly mounted triangular prism allowed to oscillate in the cross-flow direction are studied experimentally, covering the entire range of possible angles of attack. For angles of attack smaller than $\unicode[STIX]{x1D6FC}=25^{\circ }$ (where $0^{\circ }$ corresponds to the case where one of the vertices is facing the incoming flow), no oscillation is observed in the entire reduced velocity range tested. At larger angles of attack of $\unicode[STIX]{x1D6FC}=30^{\circ }$ and $\unicode[STIX]{x1D6FC}=35^{\circ }$, there exists a limited range of reduced velocities where the prism experiences vortex-induced vibration (VIV). In this range, the frequency of oscillations locks into the natural frequency twice: once approaching from the Strouhal frequencies and once from half the Strouhal frequencies. Once the lock-in is lost, there is a range with almost-zero-amplitude oscillations, followed by another range of non-zero-amplitude response. The oscillations in this range are triggered when the Strouhal frequency reaches a value three times the natural frequency of the system. Large-amplitude low-frequency galloping-type oscillations are observed in this range. At angles of attack larger than $\unicode[STIX]{x1D6FC}=35^{\circ }$, once the oscillations start, their amplitude increases continuously with increasing reduced velocity. At these angles of attack, the initial VIV-type response gives way to a galloping-type response at higher reduced velocities. High-frequency vortex shedding is observed in the wake of the prism for the ranges with a galloping-type response, suggesting that the structure’s oscillations are at a lower frequency compared with the shedding frequency and its amplitude is larger than the typical VIV-type amplitudes, when galloping-type response is observed.

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