Strouhal Number for VIV Excitation of Long Slender Structures

2018 ◽  
Author(s):  
Andrew E. Potts ◽  
Douglas A. Potts ◽  
Hayden Marcollo ◽  
Kanishka Jayasinghe
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Degrees Of Freedom ◽  
Measurement Techniques ◽  
Cross Flow ◽  
Degree Of Freedom ◽  
Circular Cylinders ◽  
Two Degrees Of Freedom ◽  
Shedding Frequency ◽  
Eddy Shedding

The prediction of Vortex-Induced Vibration (VIV) of cylinders under fluid flow conditions depends upon the eddy shedding frequency, conventionally described by the Strouhal Number. The most commonly cited relationship between Strouhal Number and Reynolds Number for circular cylinders was developed by Lienhard [1], whereby the Strouhal Number exhibits a consistent narrow band of about 0.2 (conventional across the sub-critical Re range), with a pronounced hump peaking at about 0.5 within the critical flow regime. The source data underlying this relationship is re-examined, wherein it was found to be predominantly associated with eddy shedding frequency about fixed or stationary cylinders. The pronounced hump appears to be an artefact of the measurement techniques employed by various investigators to detect eddy-shedding frequency in the wake of the cylinder. A variety of contemporary test data for elastically mounted cylinders, with freedom to oscillate under one degree of freedom (i.e. cross flow) and two degrees of freedom (i.e. cross flow and in-line) were evaluated and compared against the conventional Strouhal Number relationship. It is well established for VIV that the eddy shedding frequency will synchronise with the near resonant motions of a dynamically oscillating cylinder, such that the resultant bandwidth of lock-in exhibits a wider range of effective Strouhal Numbers than that reflected in the narrow-banded relationship about a mean of 0.2. However, whilst cylinders oscillating under one degree of freedom exhibit a mean Strouhal Number of 0.2 consistent with fixed/stationary cylinders, cylinders with two degrees of freedom exhibit a much lower mean Strouhal Number of around 0.14–0.15. Data supports the relationship that Strouhal Number does slightly diminish with increasing Reynolds Number. For oscillating cylinders, the bandwidth about the mean Strouhal Number value appears to remain largely consistent. For many practical structures in the marine environment subject to VIV excitation, such as long span, slender risers, mooring lines, pipeline spans, towed array sonar strings, and alike, the long flexible cylinders will respond in two degrees of freedom, where the identified difference in Strouhal Number is a significant aspect to be accounted for in the modelling of its dynamic behaviour.

The Numerical Research of Two-Degrees-of-Freedom Vortex-Induced Vibrations of Circular Cylinders

2012 ◽  
Vol 204-208 ◽  
pp. 4598-4601
Author(s):  
Jie Li Fan ◽  
Wei Ping Huang
Keyword(s):  
Degrees Of Freedom ◽  
Amplitude Ratio ◽  
Flow Direction ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Two Degrees Of Freedom ◽  
Line Frequency ◽  
Ansys Cfx ◽  
Vortex Induced Vibrations ◽  
Lock In

The two-degrees-of-freedom of vortex-induced vibration of circular cylinders is numerically simulated with the software ANSYS/CFX. The VIV characteristic, in the two different conditions (A/D=0.07 and A/D=1.0), is analyzed. When A/D is around 0.07, the amplitude ratio of the cylinder’s VIV between in-line and cross-flow direction in the lock-in is lower than that in the lock-out. The in-line frequency is twice of that in cross-flow direction in the lock-out, but in the lock-in, it is the same as that in cross-flow direction and the same as that of lift force. When A/D is around 1.0, the amplitude ratio of the VIV between in-line and cross-flow in the lock-in is obviously larger than that in the lock-out. Both in the lock-in and in the lock-out, the in-line frequency is twice of that in cross-flow direction.

Vorticity Shedding and Acoustic Resonance Excitation of Two Tandem Spirally Finned Cylinders in Cross-Flow

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Mohammed Alziadeh ◽  
Atef Mohany
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Root Diameter ◽  
Circular Cylinders ◽  
Resonance Excitation ◽  
Equivalent Diameter ◽  
Spacing Ratio

Abstract The aeroacoustic response of two tandem spirally finned cylinders is experimentally investigated. Three different pairs of finned cylinders are studied with fin pitch-to-root diameter ratios (p/Dr) ranging between 0.37≤p/Dr≤0.74. The spiral fins are crimped similar to those used in industrial heat exchangers. The results of the finned cylinders are compared with bare, circular cylinders with a modified equivalent diameter (Deq). The spacing ratio (L/Deq) between the cylinders are kept constant at L/Deq=2.00. The Strouhal number (StDeq) of the tandem finned cylinders is found to be higher compared to the tandem bare cylinders, resulting in an earlier onset of coincidence resonance. Moreover, unlike the tandem bare cylinders, the Strouhal number of the finned cylinders did not depend on the Reynolds number, suggesting that the flow characteristics around the finned cylinders are unaffected by Reynolds number. Only the tandem finned cylinders with the lowest fin pitch-to-root diameter ratio (p/Dr=0.37) were capable of exciting precoincidence acoustic resonance. The precoincidence resonance mechanism is similar to that observed in in-line tube bundles.

Three-Dimensional Numerical Simulations of Flows Past Smooth and Rough/Bare and Helically Straked Circular Cylinders Allowed to Undergo Two Degree-of-Freedom Motions

2007 ◽  
Author(s):  
Juan P. Pontaza ◽  
Raghu G. Menon ◽  
H. C. Chen
Keyword(s):  
Reynolds Number ◽  
Turbulence Model ◽  
Cross Flow ◽  
Operating Conditions ◽  
Degree Of Freedom ◽  
Circular Cylinders ◽  
Navier Stokes ◽  
Wall Region ◽  
Roughness Effects ◽  
Two Degree Of Freedom

We simulate the flow past smooth and rough rigid circular cylinders that are either bare or outfitted with helical stakes. We consider operating conditions that correspond to high Reynolds numbers of 105 and 106, and allow for two degree-of-freedom motions when the structure is allowed to respond to vortex-induced cross flow and in-line forces. The computations are performed using a parallelized Navier-Stokes in-house solver using overset grids. For smooth surface simulations at a Reynolds number of 105, we use a Smagorinsky Large Eddy Simulation (LES) turbulence model and for the Reynolds number cases of 106 we make use of the unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with a two-layer k-epsilon turbulence model. The rough surface modifications of the two-layer k-epsilon turbulence model due to Durbin et al. (ASME J. Fluids Eng., 2001) are implemented to account for surface roughness effects. In all our computations we aim to resolve the boundary layer directly by using adequate grid spacing in the near-wall region. The predicted global flow parameters under different surface conditions are in good agreement with experimental data and significant VIV suppression is observed when using helically straked cylinders.

Some Characteristics of Cavity Flow Past Cylindrical Inducers in a Venturi

1976 ◽  
Vol 98 (3) ◽  
pp. 461-466 ◽  
Author(s):  
B. C. Syamala Rao ◽  
D. V. Chandrasekhara
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Cavity Flow ◽  
Cavitation Number ◽  
Circular Cylinders ◽  
Two Dimensional ◽  
Wall Effects ◽  
Maximum Width ◽  
Shedding Frequency

The characteristic dimensions of the steady cavity and the shedding frequency of vortices behind six circular cylinders in a two-dimensional venturi have been studied. The normalized length and maximum width of cavity for cavitation sources of different sizes indicated unified trends with a modified cavitation number km. The angles of detachment θ increased with cavitation number k and decreased with increasing Reynolds number R. The Strouhal number Sd reached minimum values for all cavitation sources at small values of k. The possible role of wall effects on the investigations are discussed.

scholarly journals Energy and Exergy Analyses of Tube Banks in Waste Heat Recovery Applications

Energies ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 2094 ◽  
Author(s):  
Mustafa Erguvan ◽  
David MacPhee
Keyword(s):  
Energy Efficiency ◽  
Reynolds Number ◽  
Heat Recovery ◽  
Waste Heat ◽  
Cross Flow ◽  
Exergy Efficiency ◽  
Circular Cylinders ◽  
Published Data ◽  
Energy And Exergy ◽  
Exergy Analyses

In this study, energy and exergy analyses have been investigated numerically for unsteady cross-flow over heated circular cylinders. Numerous simulations were conducted varying the number of inline tubes, inlet velocity, dimensionless pitch ratios and Reynolds number. Heat leakage into the domain is modeled as a source term. Numerical results compare favorably to published data in terms of Nusselt number and pressure drop. It was found that the energy efficiency varies between 72% and 98% for all cases, and viscous dissipation has a very low effect on the energy efficiency for low Reynolds number cases. The exergy efficiency ranges from 40–64%, and the entropy generation due to heat transfer was found to have a significant effect on exergy efficiency. The results suggest that exergy efficiency can be maximized by choosing specific pitch ratios for various Reynolds numbers. The results could be useful in designing more efficient heat recovery systems, especially for low temperature applications.

VIV Response and Drag Measurements of Circular Cylinders Fitted With Permeable Meshes

2015 ◽  
Author(s):  
Murilo M. Cicolin ◽  
Gustavo R. S. Assi
Keyword(s):  
Reynolds Number ◽  
Long Range ◽  
Flow Direction ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Peak Response ◽  
Vortex Induced Vibrations ◽  
Different Types ◽  
Cylindrical Tubes ◽  
Low Mass

Experiments have been carried out on models of rigid circular cylinders fitted with three different types of permeable meshes to investigate their effectiveness in the suppression of vortex-induced vibrations (VIV). Measurements of amplitude of vibration and drag force are presented for models with low mass and damping which are free to respond in the cross-flow direction. Results for two meshes made of ropes and cylindrical tubes are compared with the VIV response of a bare cylinder and that of a known suppressor called the “ventilated trousers” (VT). All three meshes achieved an average 50% reduction of the peak response when compared with that of the bare cylinder. The sparse mesh configuration presented a similar behaviour to the VT, while the dense mesh produced considerable VIV response for an indefinitely long range of reduced velocity. All the three meshes have increased drag when compared with that of the bare cylinder. Reynolds number ranged from 5,000 to 25,000 and reduced velocity was varied between 2 and 15.

Design and Evaluation of a Multi-Degree-of-Freedom Foot/Pedal Interface for Cycling

1992 ◽  
Vol 8 (2) ◽  
pp. 152-164 ◽  
Author(s):  
Dennis Wootten ◽  
Maury L. Hull
Keyword(s):  
Knee Joint ◽  
Significant Interaction ◽  
Degrees Of Freedom ◽  
Knee Injuries ◽  
Degree Of Freedom ◽  
Two Degrees Of Freedom ◽  
Factors Affecting ◽  
Freedom Of Movement ◽  
Sample Data ◽  
Comprehensive Study

Described is the design of a foot/pedal interface intended as a research tool in the study of overuse knee injuries in cycling. The interface enables the systematic variation of factors that may affect loads transmitted by the knee joint. It permits two degrees of freedom of movement, inversion/eversion and abduction/adduction rotations, either separately or in combination. The movement permitted by each degree of freedom can be either free or resisted by spring assemblies. Sample data were collected to demonstrate the function of the foot/pedal interface. With no spring resistance, the interface functioned as intended by allowing free movement of the foot. Significant interaction was seen between the two degrees of freedom, with more motion and a larger absolute mean occurring when both degrees of freedom were allowed simultaneously. This emphasizes the need for a multi-degree-of-freedom interface when undertaking a comprehensive study of the factors affecting loads transmitted by the knee.

Development of a Fluids Laboratory Experience in Dimensional Analysis and Similitude Applied to Vortex Shedding From a Cylinder in Cross-Flow

2013 ◽  
Author(s):  
Matthew Anderson ◽  
Dylan Shiltz ◽  
Christopher Damm
Keyword(s):  
Reynolds Number ◽  
Data Acquisition ◽  
Strouhal Number ◽  
Dimensional Analysis ◽  
Vortex Shedding ◽  
Free Stream ◽  
Cross Flow ◽  
Laboratory Experience ◽  
Analysis And Design ◽  
Wide Range

A fluids laboratory experience that introduces students to dimensional analysis and similitude was designed and performed in a junior-level first course in fluid mechanics. After students are given an introduction to dimensional analysis, the technique is applied to the phenomenon of vortex shedding from a cylinder in cross-flow. With help from the instructor, lab groups use dimensional analysis to ascertain the relevant dimensionless pi terms associated with the phenomenon. After successfully determining that the pi terms are the Strouhal number and the Reynolds number, experiments are performed to elucidate the general functional relationship between the dimensionless groups. To conduct the experiments, a wind-tunnel apparatus is used in conjunction with a Pitot tube for measurements of free stream velocity and a platinum-plated tungsten hot-wire anemometer for rapid (up to 400 kHz) measurements of velocity fluctuations downstream of the cylinder. Utilizing an oscilloscope in parallel with a high-speed data acquisition system, students are able to determine the vortex shedding frequency by performing a spectral analysis (via Fourier transform) of the downstream velocity measurements at multiple free stream velocities and for multiple cylinder diameters (thus a varying Reynolds number). The students’ experimental results were found to agree with relationships found in the technical literature, showing a constant Strouhal number of approximately 0.2 over a wide range of Reynolds numbers. This exercise not only gives students valuable experience in dimensional analysis and design of experiments, it also provides exposure to modern data acquisition and analysis methods.

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