Vortex-Induced Vibrations of a Cylinder With a Control Rod in its Wake

2017 ◽  
Author(s):  
Francisco J. Huera-Huarte ◽  
José I. Jiménez-González
Keyword(s):  
Dynamic Response ◽  
Free Stream ◽  
Cross Flow ◽  
Stream Velocity ◽  
Air Bearing ◽  
Near Wake ◽  
Control Rod ◽  
Physical Mechanisms ◽  
Vortex Induced Vibrations ◽  
Damping Parameter

We study the dynamics of a flexibly-mounted cylinder having a control rod in its near wake, when subject to a uniform cross-flow. The objective is to investigate the effect of a localized perturbation introduced in the near wake of the cylinder. The work consists of a parametric study with a rigid cylinder mounted in an air bearing rig, with its motion constrained to move in the direction transverse to the flow. The cylinder system is characterised by a low combined mass-damping parameter. During the experiments, the location of the rod will be fixed, but its size and the free stream velocity will be varied. The dynamic response of the cylinder will be measured using non-intrusive techniques. The vortex dynamics in the near wake of the system will also be described after measurements obtained using Digital Image Particle Velocimetry (DPIV). The objective is to understand the physical mechanisms of the fluid-structure interaction phenomena involved in the changes of the dynamic response of the cylinder when using the control rod.

scholarly journals Modeling of Piezoelectric Energy Harvesting from Freely Oscillating Cylinders in Water Flow

2014 ◽  
Vol 2014 ◽  
pp. 1-13 ◽  
Author(s):  
Min Zhang ◽  
YingZheng Liu ◽  
ZhaoMin Cao
Keyword(s):  
Energy Harvesting ◽  
Free Stream ◽  
Piezoelectric Materials ◽  
Load Resistance ◽  
Stream Velocity ◽  
Piezoelectric Energy Harvesting ◽  
Vibratory System ◽  
System Parameters ◽  
Piezoelectric Energy ◽  
Vortex Induced Vibrations

A concept of energy harvesting from vortex-induced vibrations of a rigid circular cylinder with two piezoelectric beams attached is investigated. The variations of the power levels with the free stream velocity are determined. A mathematical approach including the coupled cylinder motion and harvested voltage is presented. The effects of the load resistance, piezoelectric materials, and circuit combined on the natural frequency and damping of the vibratory system are determined by performing a linear analysis. The dynamic response of the cylinder and harvested energy are investigated. The results show that the harvested level in SS and SP&PS modes is the same with different values of load resistance. For four different system parameters, the results show that the bigger size of cylinder with PZT beams can obtain the higher harvested power.

Influence From Helical Strakes on Vortex Induced Vibrations and Static Deflection of Drilling Risers

2005 ◽  
Author(s):  
Carl M. Larsen ◽  
Gro Sagli Baarholm ◽  
Halvor Lie
Keyword(s):  
Dynamic Response ◽  
Test Data ◽  
Oscillation Amplitude ◽  
Cross Flow ◽  
Current Profile ◽  
Dynamic Stresses ◽  
Drag Forces ◽  
Vortex Induced Vibrations ◽  
Bending Stresses ◽  
Helical Strakes

Helical strakes are known to reduce and even eliminate the oscillation amplitude of vortex induced vibrations (VIV). This reduction will increase fatigue life, and also reduce drag magnification from cross-flow vibrations. But sections with strakes will also have a larger drag coefficient than the bare riser. Hence, the extension of a section with strakes along a riser should be large enough to reduce oscillations, but not too long in order to limit drag forces from current and waves. The optimum length and position for a given riser will therefore vary with current profile. Dynamic response from waves should also be taken into account. The purpose of the present paper is to illustrate the influence from strakes on VIV, as well as on static and dynamic response for a drilling riser. Hydrodynamic coefficients for a cylinder with helical strakes are found from experiments and applied in an empirical model for the analysis of VIV. The result from the VIV analysis is used for a second calculation of drag forces that are applied in an updated static analysis. Dynamic stresses from regular waves are also presented, but VIV are not considered for these cases. A simple study of length and position of the section with strakes is carried out for some standard current profiles. Results are presented in terms of oscillation amplitudes, fatigue damage, bending stresses and riser angles at ends. The study is based on test data for one particular strake geometry, but the analysis method as such is general, and the computer programs used in the study can easily apply other test data.

Recent Advances in Pipeline Free Span Design: A New Revision of DNV-RP-F105

2016 ◽  
Author(s):  
Knut Vedeld ◽  
Håvar Sollund ◽  
Olav Fyrileiv
Keyword(s):  
Dynamic Response ◽  
Limit State ◽  
Cross Flow ◽  
Ease Of Use ◽  
Direct Result ◽  
Ultimate Limit State ◽  
Vortex Induced Vibrations ◽  
Load Effects ◽  
Pipeline Design ◽  
Wave Induced

Pipeline free span design has evolved from basic avoidance criteria in the DNV ’76 rules [1], to fatigue and ultimate limit state considerations in Guideline no. 14 [2]. Modern multimode, multi-span free span design is predominantly performed according to DNV-RP-F105 [3]. In 2006, the latest revision of DNV-RP-F105 [3] was written as a direct result of extensive research, performed due to significant free span challenges in the Ormen Lange pipeline project. DNV-RP-F105 was at the time, and still is, the only pipeline design code giving contemporary design guidance for vortex induced vibrations (VIV) and direct wave loading design for pipelines in free spans. The last revision of DNV-RP-F105 included a few, but highly important advances, particularly the consideration for multi-mode and multi-span pipeline dynamic response behavior. In the 10 years that have followed, no breakthroughs of similar magnitude have been achieved for pipeline free spans, but a large number of incremental improvements to existing calculation methods, and some novel advances in less critical aspects of VIV understanding have been made. As a result, DNV-RP-F105 has recently been revised to account for these advances, which include improved frequency-domain analyses of wave-induced fatigue, a new response model for cross-flow VIV in low Keulegan-Carpenter (KC) regimes in pure waves, new analytical methods for dynamic response calculations of short spans in harsh conditions, and extensive guidance on how to apply the recommended practice for assessment of fatigue and extreme environmental load effects on curved structural members such as spools, jumpers and manifold flexloops. This paper gives an overview of most of the important changes and updates to the new revision of DNV-RP-F105. Case studies are used to demonstrate the importance and effects of the changes made, and to some extent how the revision of DNV-RP-F105 can enhance its applicability and ease of use.

Jet Interaction in Cross Flow: Experimental and Numerical Model

2014 ◽  
Author(s):  
Celso Almeida ◽  
António A. Nunes ◽  
Senhorinha Teixeira ◽  
José Carlos Teixeira ◽  
Pedro Lobarinhas
Keyword(s):  
Wind Tunnel ◽  
Cross Section ◽  
Large Scale ◽  
Cfd Simulation ◽  
Free Stream ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Stream Velocity ◽  
Entire Cross Section ◽  
Injection Point

Ventilation of wide spaces often requires a correct mixing of a jet in a cross flow. The present paper describes the application of Computational Fluid Dynamics (CFD) to model the interaction of a free stream jet with a cross flow, taking into account temperature gradients between the two streams. The model uses the finite volume technique for solving the conservation equations of fluid: mass, momentum and energy. Buoyancy is described by the Boussinesq approximation. The convergence of the solution required a high mesh refinement in the region of flow interaction. The data were compared with experimental results obtained in a subsonic wind tunnel. The experiments were carried out along the 4.0 m long test section of a 1.4×0.8 low speed wind tunnel. The jets were injected at 90° through orifices 25 mm in diameter drawn from a plenum either at the same or higher temperature the free stream. The jet velocity to the free stream velocity ratio was set at 8 for a single jet and between 4 and 16 for multiple injections. Data include velocity, pressure and temperature. The results show that the injection of relatively small cross-flow rates can cause the development of large regions of interaction with the main flux, accompanied by the creation of large scale flow structures, which contribute effectively to rapid mixing of the two streams. A CFD simulation of temperature showed that a jet 30 diameters downstream (30D) is an extension of the plume covering almost half of the cross section and a good homogeneity, then the extension of the plume 120D which covers almost the entire cross section and an optimum mixing occurs. The CFD simulation temperature of 13 jets showed that a toroidal extension of the plume and a good homogenization as early as 30D downstream of the injection point, occurs.

Boundary Layer Calculation for Analysis and Design

1978 ◽  
Vol 100 (2) ◽  
pp. 232-236 ◽  
Author(s):  
H. E. Weber
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Turbulent Flows ◽  
Free Stream ◽  
Cross Flow ◽  
Semiempirical Method ◽  
Stream Velocity ◽  
Potential Core ◽  
Analysis And Design ◽  
Inlet Conditions

A simple, semiempirical method for calculating the laminar, transition, and turbulent boundary layer with arbitrary free stream pressure gradient is developed. Good correlation is obtained with data on general two dimensional turbulent flows, diffuser flows, and the cylinder in cross-flow. However only for the diffuser has the boundary layer flow been coupled with the potential core so that only the inlet conditions and geometry are required. In other cases the free stream velocity distribution must be known or calculable. Skin friction coefficient, momentum thickness Reynolds number, and free stream pressure gradient parameter correlation employs a simple lag theory. With the integral momentum equation the complete boundary layer parameters are obtained as functions of the distance along a surface.

Three-dimensional laminar boundary layers in crosswise pressure gradients

1974 ◽  
Vol 66 (4) ◽  
pp. 641-655 ◽  
Author(s):  
J. H. Horlock ◽  
A. K. Lewkowicz ◽  
J. Wordsworth
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Free Stream ◽  
Three Dimensional ◽  
Cross Flow ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Laminar Boundary Layers ◽  
The Cross

Two attempts were made to develop a three-dimensional laminar boundary layer in the flow over a flat plate in a curved duct, establishing a negligible streamwise pressure gradient and, at the same time, an appreciable crosswise pressure gradient.A first series of measurements was undertaken keeping the free-stream velocity at about 30 ft/s; the boundary layer was expected to be laminar, but appears to have been transitional. As was to be expected, the cross-flow in the boundary layer decreased gradually as the flow became progressively more turbulent.In a second experiment, at a lower free-stream velocity of approximately 10 ft/s, the boundary layer was laminar. Its streamwise profile resembled closely the Blasius form, but the cross-flow near the edge of the boundary layer appears to have exceeded that predicted theoretically. However, there was a substantial experimental scatter in the measurements of the yaw angle, which in laminar boundary layers is difficult to obtain accurately.

Free-stream turbulence and the development of cross-flow disturbances

2013 ◽  
Vol 735 ◽  
pp. 347-380 ◽  
Author(s):  
Robert S. Downs ◽  
Edward B. White
Keyword(s):  
Surface Roughness ◽  
Flow Problem ◽  
Free Stream ◽  
Flow Instability ◽  
Cross Flow ◽  
Stream Velocity ◽  
Swept Wing ◽  
Free Stream Turbulence ◽  
Flow Disturbances ◽  
The Cross

AbstractThe cross-flow instability that arises in swept-wing boundary layers has resisted attempts to describe the path from disturbance initiation to transition. Following concerted research efforts, surface roughness and free-stream turbulence have been identified as the leading providers of initial disturbances for cross-flow instability growth. Although a significant body of work examines the role of free-stream turbulence in the cross-flow problem, the data more relevant to the flight environment (turbulence intensities less than 0.07 %) are sparse. A series of recent experiments indicates that variations within this range may affect the initiation or growth of cross-flow instability amplitudes, hindering comparison among results obtained in different disturbance environments. To address this problem, a series of wind tunnel experiments is performed in which the free-stream turbulence intensity is varied between 0.02 % and 0.2 % of free-stream velocity,${U}_{\infty } $. Measurements of the stationary and travelling mode amplitudes are made in the boundary layer of a 1.83 m chord,$45{{}^\circ} $swept-wing model. These results are compared to those of similar experiments at higher turbulence levels to broaden the current knowledge of this portion of the cross-flow problem. It is observed that both free-stream turbulence and surface roughness contribute to the initiation of unsteady disturbances, and that free-stream turbulence affects the development of both stationary and unsteady cross-flow disturbances. For the range tested, enhanced free-stream turbulence advances the transition location except when a subcritically spaced roughness array is employed.

Effect of Corner Cut on the Near Wake Flow Structures of a Square Cylinder

2014 ◽  
Author(s):  
Hariprasad Chakkalaparambil Many ◽  
Nagella Yashwanth ◽  
Haresh Bhardwaj ◽  
R. Ajith Kumar ◽  
B. H. Lakshmana Gowda
Keyword(s):  
Free Stream ◽  
Wake Flow ◽  
Practical Significance ◽  
Flow Structures ◽  
Stream Velocity ◽  
Square Cylinder ◽  
Sinusoidal Oscillation ◽  
Near Wake ◽  
Almost All ◽  
Sharp Corners

In this paper, results of a flow visualization study on the flow around a square section cylinder with corner chamfering are presented. The corners of the cylinder are chamfered so that the each corner forms a triangle with horizontal (stream-wise) and cross stream (perpendicular to the free stream velocity) dimension ‘b’. Experiments are conducted for b/B0 ratios of 0.05, 0.1, 0.2 and 0.3 where ‘B0’ is the side dimension of the uncut square cylinder. The flow structures, particularly the vortex shedding mode and mechanism around the cylinder with chamfered corners are investigated in order to deduce the effect of corner modifications on the flow. For studies with stationary cylinder (case (a)), the results are taken at Reynolds number values of 1500, 2100 and 2800. For sinusoidally oscillated cylinder case (case (b)), the studies are restricted to Re=2100. To bring out the effect of corner chamfering more clearly, experiments are also conducted with a square cylinder without corner cuts, i.e., with sharp corners. For the case (b), a special mechanism is made to oscillate the cylinders at a desired amplitude and frequency. That is, the cylinder undergoes forced sinusoidal oscillation in case (b). It is found that drag decreases and Strouhal number increases with b/B0 ratio. Quite uniquely, at b/B0=0.2, cross-stream convection of vortices have been observed. Vortex coalescence is observed in almost all cases. Results indicate that corner chamfering brings notable changes in the near-wake flow structures of a square section cylinder. In view of marine structures and building sections with similar geometries, the present results carry considerable practical significance.

INFLUENCE OF THE INLET SHAPE ON THE PERFORMANCE OF DOUBLE OFFSET TRANSITION S-DUCT WITH DIFFUSION

2008 ◽  
Vol 05 (01) ◽  
pp. 1-19 ◽  
Author(s):  
RAJESH KUMAR SINGH ◽  
SIDHNATH SINGH ◽  
V. SESHADRI
Keyword(s):  
Total Pressure ◽  
Free Stream ◽  
Flow Behavior ◽  
Flow Analysis ◽  
Cross Flow ◽  
Area Ratio ◽  
Stream Velocity ◽  
Crucial Component ◽  
Flow Investigation ◽  
Cross Flow Velocity

Transition S-shaped intake duct is a crucial component of dual engine used in modern combat aircrafts. Present flow investigation demonstrates the flow behavior of double offset transition S-duct for different inlet geometries having circular exit (ϕ = 72.5 mm) and uniform roughness. The inlet geometries namely rectangular, square, elliptical, oval, and semicircular have been analyzed for double offset transition S-duct having 300 mm centerline length and an area ratio of 2.0. Incompressible flow analysis carried out for free stream velocity at 30 m/s with RNG k–ε turbulence model has shown that the elliptical inlet shape gives the best performance whereas square inlet gives the worst performance in terms of longitudinal and cross-flow velocity distribution, pressure recovery, total pressure loss, distortion coefficient, and swirl coefficient at the exit of the duct.

scholarly journals Effects of Elevated Free-Stream Turbulence on Flow and Thermal Structures in Transitional Boundary Layers

1993 ◽  
Author(s):  
Dadong Zhou ◽  
Ting Wang
Keyword(s):  
Boundary Layers ◽  
Free Stream ◽  
Formation Rate ◽  
Heat Fluxes ◽  
Stream Velocity ◽  
Reynolds Stresses ◽  
Free Stream Turbulence ◽  
Physical Mechanisms ◽  
Thermal Structures ◽  
Transition Length

The effects of elevated free-stream turbulence on flow and thermal structures in transitional boundary layers were investigated experimentally on a heated flat plate. Detailed boundary layer measurements using a three-wire probe and wall heat transfer were made with free-stream turbulence intensities of 0.5, 3.8, 5.5 and 6.4 percent respectively. The onset of transition, transition length and the turbulent spot formation rate were determined. The statistical results of the streamwise and cross-stream velocity fluctuations, temperature fluctuation, Reynolds stresses and Reynolds heat fluxes were presented. The eddy viscosity, turbulent thermal diffusivity and the turbulent Prandtl number were calculated and related physical mechanisms are discussed.

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