Closely Spaced Circular Cylinders in Cross-Flow and a Universal Wake Number

2004 ◽  
Vol 126 (2) ◽  
pp. 245-249 ◽  
Author(s):  
David Sumner
Keyword(s):  
Vortex Shedding ◽  
Bluff Body ◽  
Incidence Angle ◽  
Cross Flow ◽  
Base Pressure ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Aerodynamic Forces ◽  
Single Vortex ◽  
Total Drag

To investigate the effectiveness of a universal wake number for groups of closely spaced bluff bodes, staggered cylinder configurations with center-to-center pitch ratios of P/D=1.125 and 1.25, and incidence angles from α=0 deg–90 deg, were tested in the subcritical Reynolds number regime. The aerodynamic forces, base pressure, and vortex shedding frequencies were measured for the upstream and downstream cylinders, and were found to be strongly dependent on the incidence angle and small changes in the flow pattern. The Griffin number was found to be an appropriate universal wake number for the closely spaced staggered cylinders, based on the total drag force acting on the two cylinders, and the average base pressure for the two cylinders. The results suggest that the single vortex wake of a pair of closely spaced staggered cylinders is broadly comparable to the wake of a solitary bluff body, and that the universal wake number concept can be extended to groups of closely spaced bluff bodies.

Vortex Shedding From Two Circular Cylinders in a Staggered Arrangement

2003 ◽  
Author(s):  
D. Sumner ◽  
M. D. Richards
Keyword(s):  
Strouhal Number ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Incidence Angle ◽  
Power Spectra ◽  
Circular Cylinders ◽  
Aerodynamic Forces ◽  
Staggered Arrangement ◽  
Pitch Ratio ◽  
Small Increments

Vortex shedding from two circular cylinders of equal diameter in a staggered configuration was studied experimentally in the subcritical Reynolds number regime, for Re = 3.2×104–7.4×104. The dimensionless centre-to-centre pitch ratio of the staggered cylinders was ranged from P/D = 1.125–4.0, and the incidence angle was varied in small increments from α = 0°–90°. The behaviour of the Strouhal number measurements was broadly classified according to whether the cylinders were closely, moderately, or widely spaced, corresponding to P/D < 1.5, 1.5 ≤ P/D ≤ 2.5, and P/D > 2.5, respectively. For closely spaced staggered configurations, the flow around the cylinders is similar to a single bluff body, and only a single Strouhal number is measured. For moderately spaced cylinders, two distinct Strouhal numbers are measured when α > 30°, but there is considerable scatter in the Strouhal data when α < 30°. For widely spaced cylinders, the Strouhal numbers remain close to that of a single circular cylinder, in contrast to the behaviour of the aerodynamic forces. Evidence of the outer lift peak is seen in the power spectra for the downstream cylinder.

An Experimental Investigation of Staggered Circular Cylinders in a Uniform Planar Shear Flow

2002 ◽  
Author(s):  
O. O. Akosile ◽  
D. Sumner
Keyword(s):  
Shear Flow ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Incidence Angle ◽  
Lift Coefficient ◽  
Circular Cylinders ◽  
Aerodynamic Forces ◽  
Planar Shear ◽  
Critical Incidence

Two circular cylinders of equal diameter, arranged in staggered configurations of P/D = 1.125 and 1.25, were immersed in a uniform planar shear flow, at Re = 5.0×104 and a dimensionless shear parameter of K = 0.05. The mean aerodynamic forces and the vortex shedding frequencies were measured for the upstream and downstream cylinders at each P/D. Under uniform, no-shear flow conditions, K = 0, the flow field of the cylinder group is similar to a single bluff body. As the incidence angle is varied from α = 0° to 90°, the forces on each cylinder undergo discontinuous changes, or attain local minimum or maximum values, at several critical incidence angles. At small α, the Strouhal number is greater than that of a single, isolated circular cylinder, whereas at high α the Strouhal number is lower than the single-cylinder value. The effects of shear, K = 0.05, on the aerodynamic forces were different depending on whether the downstream cylinder was situated at a higher or lower centreline velocity compared to the upstream cylinder. The planar shear flow had its greatest influence when the cylinders were in a nearly side-by-side arrangement. This indicated that the effect of shear was mostly on the flow through the gap between the cylinders. The lift coefficient data were mostly unchanged by the shear flow, the drag coefficient data were lowered, and there were shifts in the critical incidence angles. The influence of shear on vortex shedding was less pronounced, but there was a small reduction in Strouhal number compared to the no-shear case.

Vortex shedding from bluff bodies in a shear flow

1973 ◽  
Vol 60 (2) ◽  
pp. 401-409 ◽  
Author(s):  
D. J. Maull ◽  
R. A. Young
Keyword(s):  
Shear Flow ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Pressure Coefficient ◽  
Uniform Flow ◽  
Base Pressure ◽  
Longitudinal Vortex ◽  
Bluff Bodies ◽  
Stream Direction

Experiments are described in which the vortex shedding from a bluff body and the base pressure coefficient have been measured in a shear flow. It is shown that the shedding breaks down into a number of spanwise cells in each of which the frequency is constant. The division between the cells is thought to be marked by a longitudinal vortex in the stream direction and this is supported by evidence from experiments where a longitudinal vortex was generated in an otherwise uniform flow.

Numerical characterization of three-dimensional bluff body shear layer behaviour

2016 ◽  
Vol 799 ◽  
pp. 1-26 ◽  
Author(s):  
Daniel T. Prosser ◽  
Marilyn J. Smith
Keyword(s):  
Shear Layer ◽  
Turbulent Flows ◽  
Bluff Body ◽  
Separation Bubble ◽  
Incidence Angle ◽  
Three Dimensional ◽  
Circular Cylinders ◽  
Time Averaging ◽  
Bluff Bodies ◽  
Face Shape

Three-dimensional bluff body aerodynamics are pertinent across a broad range of engineering disciplines. In three-dimensional bluff body flows, shear layer behaviour has a primary influence on the surface pressure distributions and, therefore, the integrated forces and moments. There currently exists a significant gap in understanding of the flow around canonical three-dimensional bluff bodies such as rectangular prisms and short circular cylinders. High-fidelity numerical experiments using a hybrid turbulence closure that resolves large eddies in separated wakes close this gap and provide new insights into the unsteady behaviour of these bodies. A time-averaging technique that captures the mean shear layer behaviours in these unsteady turbulent flows is developed, and empirical characterizations are developed for important quantities, including the shear layer reattachment distance, the separation bubble pressure, the maximum reattachment pressure, and the stagnation point location. Many of these quantities are found to exhibit a universal behaviour that varies only with the incidence angle and face shape (flat or curved) when an appropriate normalization is applied.

Vortex shedding from bluff bodies in oscillatory flow: A report on Euromech 119

1980 ◽  
Vol 99 (2) ◽  
pp. 225-245 ◽  
Author(s):  
P. W. Bearman ◽  
J. M. R. Graham
Keyword(s):  
Vortex Shedding ◽  
Oscillatory Flow ◽  
Bluff Body ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Unidirectional Flow ◽  
Low Reynolds Number Flows ◽  
Wide Range ◽  
Bluff Body Flow ◽  
Reynolds Number Flows

European Mechanics Colloquium number 119 was held at Imperial College on 16–18 July 1979, when the subject of vortex shedding from bodies in unidirectional flow and oscillatory flow, was discussed. A wide range of experimental work was presented including low-Reynolds-number flows around circular cylinders, the influence of disturbances on bluff body flow, the measurement of fluctuating forces and the influence of oscillations of the stream. About a third of the 33 papers presented concentrated on theoretical aspects and the majority of these were concerned with the ‘method of discrete vortices’.

A Closer Investigation of the Mean Aerodynamic Forces for Two Staggered Circular Cylinders in Cross-Flow

2002 ◽  
Author(s):  
D. Sumner ◽  
M. D. Richards
Keyword(s):  
Reynolds Number ◽  
Shear Layer ◽  
Incidence Angle ◽  
Cross Flow ◽  
Local Maximum ◽  
Circular Cylinders ◽  
Aerodynamic Forces ◽  
Gap Flow ◽  
The Mean ◽  
Small Increments

Two circular cylinders of equal diameter in a staggered configuration, with centre-to-centre pitch ratios of P/D = 1.125 – 4.0, were tested in the subcritical Reynolds number regime, at Re = 3.0×104 – 8.0×104. The incidence angle of the cylinder configuration was varied in small increments from α = 0° – 90° and the mean aerodynamic forces were measured on both the upstream and downstream cylinders. Based on the force measurements, the behaviour of the cylinders was broadly grouped into three categories, depending on P/D. For closely spaced staggered configurations, P/D = 1.125 – 1.25, the aerodynamic forces on both the upstream and downstream cylinders varied significantly with α. Several critical incidence angles were identified for each cylinder that corresponded to local maximum, minimum, or discontinuous behaviour in the forces, which were related to shear layer reattachment and the influence of the gap flow. For moderately spaced staggered configurations, P/D = 1.5 – 2.5, shear layer reattachment and the subsequent transition to gap flow at small α were responsible for the inner lift peak, a corresponding minimum drag, and a loss of lift with increasing α, which becomes more abrupt as P/D is increased. For widely spaced staggered configurations, P/D = 3.0 – 4.0, the two cylinders undergo Ka´rma´n vortex shedding for the entire range of α. At small α, the forces on the downstream cylinder are affected by vortex impingement, and the outer lift peak replaces the inner lift peak. This outer lift peak exhibits some sensitivity to the Reynolds number.

Appraisal of Universal Wake Numbers From Data for Roughened Circular Cylinders

1983 ◽  
Vol 105 (4) ◽  
pp. 464-468 ◽  
Author(s):  
G. Buresti
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Drag Coefficient ◽  
Vortex Shedding ◽  
Physical Interpretation ◽  
Potential Flow ◽  
Bluff Body ◽  
Cross Flow ◽  
Sufficient Accuracy ◽  
Circular Cylinders

An analysis was carried out to check whether certain existing universal wake numbers can characterize the cross-flow around roughened circular cylinders in transitional regimes. The results confirmed the soundness of the idea of the existence of a link between the drag coefficient of a bluff body, its pressure distribution, and the frequency of the shedding of vortices in its wake. In particular, Bearman’s number and Griffin’s number were shown to be able to describe this link with sufficient accuracy and to be a function of the Reynolds number based on the typical dimension of the surface roughness. A physical interpretation of Griffin’s number was also given which permits to link the drag force with the velocity of the potential flow at separation and the frequency of vortex shedding.

Aerodynamics of a two-dimensional bluff body with the cross-section of a train

2020 ◽  
Vol 23 (12) ◽  
pp. 2679-2693 ◽  
Author(s):  
Huan Li ◽  
Xuhui He ◽  
Hanfeng Wang ◽  
Si Peng ◽  
Shuwei Zhou ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Large Amplitude ◽  
High Speed ◽  
Bluff Body ◽  
Mean Amplitude ◽  
Two Dimensional ◽  
Aerodynamic Forces ◽  
Moderate Reynolds Number ◽  
Amplitude Mode

Experiments on the aerodynamics of a two-dimensional bluff body simplified from a China high-speed train in crosswinds were carried out in a wind tunnel. Effects of wind angle of attack α varying in [−20°, 20°] were investigated at a moderate Reynolds number Re = 9.35 × 104 (based on the height of the model). Four typical behaviors of aerodynamics were identified. These behaviors are attributed to the flow structure around the upper and lower halves of the model changing from full to intermittent reattachment, and to full separation with a variation in α. An alternate transition phenomenon, characterized by an alteration between large- and small-amplitude aerodynamic fluctuations, was detected. The frequency of this alteration is about 1/10 of the predominant vortex shedding. In the intervals of the large-amplitude behavior, aerodynamic forces fluctuate periodically with a strong span-wise coherence, which are caused by the anti-symmetric vortex shedding along the stream-wise direction. On the contrary, the aerodynamic forces fluctuating at small amplitudes correspond to a weak span-wise coherence, which are ascribed to the symmetric vortex shedding from the upper and lower halves of the model. Generally, the mean amplitude of the large-amplitude mode is 3 times larger than that of the small one. Finally, the effects of Reynolds number were examined within Re = [9.35 × 104, 2.49 × 105]. Strong Reynolds number dependence was observed on the model with two rounded upper corners.

scholarly journals Kill Line Model Cross Flow Inline Coupled Vortex-Induced Vibration

2017 ◽  
Author(s):  
Baiheng Wu ◽  
Jorlyn Le Garrec ◽  
Dixia Fan ◽  
Michael S. Triantafyllou
Keyword(s):  
Bluff Body ◽  
Oil And Gas ◽  
Cross Flow ◽  
The Body ◽  
Bluff Bodies ◽  
Structural Vibrations ◽  
Vortex Induced Vibrations ◽  
Series Of Experiments ◽  
Central Pipe ◽  
Semi Empirical

Currents and waves cause flow-structure interaction problems in systems installed in the ocean. Particularly for bluff bodies, vortices form in the body wake, which can cause strong structural vibrations (Vortex-Induced Vibrations, VIV). The magnitude and frequency content of VIV is determined by the shape, material properties, and size of the bluff body, and the nature and velocity of the oncoming flow. Riser systems are extensively used in the ocean to drill for oil wells, or produce oil and gas from the bottom of the ocean. Risers often consist of a central pipe, surrounded by several smaller cylinders, including the kill and choke lines. We present a series of experiments involving forced in-line and cross flow motions of short rigid sections of a riser containing 6 symmetrically arranged kill and choke lines. The experiments were carried out at the MIT Towing Tank. We present a systematic database of the hydrodynamic coefficients, consisting of the forces in phase with velocity and the added mass coefficients that are also suitable to be used with semi-empirical VIV predicting codes.

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