Wake Formation From a Pair of Circular Cylinders Traversing Between Small- and Large-Incidence Flow Regimes

2012 ◽  
Vol 134 (1) ◽  
Author(s):  
Mir M. A. Hayder
Keyword(s):  
Oscillation Amplitude ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Mean Flow ◽  
Pitch Ratio ◽  
Oscillation Frequencies ◽  
Hot Film ◽  
Stagger Angle ◽  
Wake Formation

Cross flow past a pair of equal-diameter staggered circular cylinders, with either one of the pair subject to forced harmonic transverse oscillation, is investigated experimentally within Reynolds numbers Re = 525–750. The center-to-center pitch ratio and stagger angle of the cylinders at their mean position are 2.5° and 21°, respectively. Results with cylinder excitation frequencies in the range 0.07 ≤ feD/U ≤ 1.18 (D = cylinder diameter, U = mean flow velocity) at a constant oscillation amplitude (peak-to-peak) of 0.44D are reported. Flow visualization of the wake formation region and hot-film measurements of the wake velocity are reported. Emphasis is placed on the mechanisms leading to vortex shedding. Results show that the wake undergoes considerable modification with the oscillation of either of the two cylinders; this modification depends strongly on the value of feD/U. The flow patterns remain essentially the same as those of the corresponding static cases for feD/U < 0.10. However, the flow at higher oscillation frequencies than that can no longer maintain those patterns. In particular, there are distinct regions of fundamental and superharmonic synchronizations between the dominant wake periodicities and the cylinder oscillation over the whole range of feD/U. Moreover, the manner in which the wake responds to the cylinder oscillation depends strongly on whether it is the upstream or downstream cylinder which is being oscillated.

Wake Formation for an Oscillating Small-Incidence-Angle Cylinder Pair in Cross-Flow

2011 ◽  
Author(s):  
Mir M. Hayder
Keyword(s):  
Incidence Angle ◽  
Flow Direction ◽  
Incident Angle ◽  
Cross Flow ◽  
Wake Flow ◽  
Circular Cylinders ◽  
Mean Flow ◽  
Small Incidence ◽  
The Mean ◽  
Wake Formation

The wake region of a pair of equal-diameter staggered circular cylinders in cross-flow is investigated experimentally for Reynolds numbers, based on the mean flow velocity, U, and the cylinder diameter, D, within the range 540 ≤ Re ≤ 755. The centre-to-centre pitch ratio and stagger angle of the cylinders at their mean position are P/D = 2.0 and α = 16°, respectively. In an earlier study, wake formation of a small-incident-angle cylinder pair was investigated for forced oscillation (transverse to the flow direction) of the upstream cylinder only. The present study is aimed to reveal the modification of the wake when the oscillation is shifted from the upstream to downstream cylinder or vice versa. Results with cylinder excitation frequencies in the range 0.07 ≤ feD/U ≤ 1.10 are reported. It is observed that for both upstream and downstream cylinder oscillations with frequency feD/U ≤ 0.10 the wake flow patterns remain essentially the same as those of the corresponding static cases. However, for frequency feD/U &gt; 0.10 the wake undergoes considerable modification vis-a`-vis when the cylinders are stationary, and the flow pattern within the wake is strongly dependent on feD/U value. As also observed in the previous study, there are distinct regions of synchronization between the dominant wake periodicities and the cylinder oscillation over the whole range of feD/U. These synchronizations involve sub- and super-harmonics as well as fundamental synchronizations and are the result of the formation of two rows of vortices, one on either side of the combined wake of the cylinder pair. The manner in which the wake responds to the cylinder oscillation depends strongly on whether it is the upstream or downstream cylinder which is oscillating. Flow-visualization images suggests that the synchronizations on the mean-flow side of the downstream cylinder occur from the outer vortices shed by the downstream cylinder, and those on the mean-flow side of the upstream cylinder occur from the vortices formed by the interaction of the two gap shear layers and the outer shear layer separated from the upstream cylinder.

Cross-Flow Past a Pair of Staggered Cylinders With the Upstream Cylinder Subjected to a Transverse Harmonic Oscillation

2002 ◽  
Author(s):  
Stuart J. Price ◽  
Srikanth Krishnamoorthy ◽  
Michael P. Pai¨doussis
Keyword(s):  
Flow Direction ◽  
Vortex Formation ◽  
Cross Flow ◽  
Harmonic Oscillation ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Flow Past ◽  
The Mean ◽  
Lock In ◽  
Hot Film

An experimental investigation of the cross-flow past a pair of staggered circular cylinders, with the downstream cylinder subject to forced harmonic oscillation transverse to the flow direction, is presented in this paper. In particular, flow-visualization of the wakeformation region and hot-film measurements of the wake spectra are reported. Experiments were conducted in a water tunnel for Reynolds numbers, based on upstream velocity, U, and cylinder diameter, D, in the range 1440 ≤ Re ≤ 1680. The longitudinal separation between cylinder centers is L/D = 2.0, with a transverse separation (for the mean position of the upstream cylinder) of T/D = 0.17. As shown in an earlier study, depending on the actual position of the upstream cylinder in its oscillation cycle, this configuration straddles the shear-layer reattachment and induced separation regimes. The results show that the oscillation of the upstream cylinder causes considerable modification of the flow patterns and regimes compared to what is obtained when the cylinder is fixed. In particular, depending on the frequency of oscillation of the upstream cylinder, sub- and superharmonic resonances are obtained between the vortex formation frequency and oscillation frequency, as well as the usual fundamental lock-in. These resonances and accompanying wake regimes are examined in detail in this paper.

Cross-Flow Past a Pair of Staggered Cylinders With the Upstream Cylinder Subjected to a Transverse Harmonic Oscillation

2006 ◽  
Author(s):  
Stuart J. Price ◽  
Michael P. Pai¨doussis ◽  
Srikanth Krishnamoorthy
Keyword(s):  
Flow Direction ◽  
Vortex Formation ◽  
Cross Flow ◽  
Harmonic Oscillation ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Vortex Pairing ◽  
Flow Past ◽  
Lock In ◽  
Hot Film

The results of an experimental investigation are presented for the cross-flow past a pair of staggered circular cylinders, with the upstream cylinder being subject to forced harmonic oscillation transverse to the flow direction. Flow-visualization of the wake-formation region and hot-film measurements of the wake spectra are reported. Experiments were conducted in a water tunnel for Reynolds numbers, based on upstream velocity, U, and cylinder diameter, D, in the range 1440 ≤ Re ≤ 1680. Results are presented for the case where the longitudinal separation between cylinder centres (for the mean position of the upstream cylinder) is L/D = 2.0, with the transverse separation being T/D = 1.0. As shown by Sumner et al. [1] this configuration corresponds to either the gap vortex pairing and enveloping or gap vortex pairing, splitting and enveloping regimes. The results show that the oscillation of the upstream cylinder causes considerable modification of the flow patterns and regimes compared to what is obtained when the cylinder is fixed. In particular, depending on the frequency of oscillation of the upstream cylinder, sub- and super-harmonic resonances are obtained between the vortex formation frequency and oscillation frequency, as well as the usual fundamental lock-in. These resonances and accompanying wake regimes are examined in detail in the paper.

A Model for High-Reynolds-Number Flow Past Rough-Walled Circular Cylinders

1977 ◽  
Vol 99 (3) ◽  
pp. 486-493 ◽  
Author(s):  
O. Gu¨ven ◽  
V. C. Patel ◽  
C. Farell
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Circular Cylinder ◽  
Turbulent Boundary Layer ◽  
Pressure Coefficient ◽  
Empirical Relation ◽  
Reynolds Numbers ◽  
Boundary Layer Separation ◽  
Circular Cylinders ◽  
Mean Flow

A simple analytical model for two-dimensional mean flow at very large Reynolds numbers around a circular cylinder with distributed roughness is presented and the results of the theory are compared with experiment. The theory uses the wake-source potential-flow model of Parkinson and Jandali together with an extension to the case of rough-walled circular cylinders of the Stratford-Townsend theory for turbulent boundary-layer separation. In addition, a semi-empirical relation between the base-pressure coefficient and the location of separation is used. Calculation of the boundary-layer development, needed as part of the theory, is accomplished using an integral method, taking into account the influence of surface roughness on the laminar boundary layer and transition as well as on the turbulent boundary layer. Good agreement with experiment is shown by the results of the theory. The significant effects of surface roughness on the mean-pressure distribution on a circular cylinder at large Reynolds numbers and the physical mechanisms giving rise to these effects are demonstrated by the model.

Flow-pattern identification for two staggered circular cylinders in cross-flow

2000 ◽  
Vol 411 ◽  
pp. 263-303 ◽  
Author(s):  
D. SUMNER ◽  
S. J. PRICE ◽  
M. P. PAÏDOUSSIS
Keyword(s):  
Particle Image ◽  
Cross Flow ◽  
Flow Patterns ◽  
Shear Layers ◽  
Circular Cylinders ◽  
Angle Of Incidence ◽  
Vortex Pairing ◽  
Image Velocimetry ◽  
Pitch Ratio ◽  
Flow Pattern Identification

The flow around two circular cylinders of equal diameter, arranged in a staggered configuration, was investigated using flow visualization and particle image velocimetry for centre-to-centre pitch ratio P/D = 1[ratio ]0 to 5.0 and angle of incidence. α = 0° to 90°. Experiments were conducted within the low subcritical Reynolds number regime, from Re = 850 to 1900. Nine flow patterns were identified, and processes of shear layer reattachment, induced separation, vortex pairing and synchronization, and vortex impingement, were observed. New insight was gained into previously published Strouhal number data, by considering the flow patterns involved. The study revealed that vortex shedding frequencies are more properly associated with individual shear layers than with individual cylinders; more specifically, the two shear layers from the downstream cylinder often shed vortices at different frequencies.

Model Test on Drag of Cylinders With Helical Grooves at High Reynolds Numbers

2010 ◽  
Author(s):  
Shan Huang ◽  
Neil Kitney
Keyword(s):  
Model Test ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Tank Model ◽  
Towing Tank ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
Helical Grooves ◽  
Four Cylinders

Towing tank model tests at high Reynolds numbers, up to 1.1×106, were carried out in order to investigate the effects of the triple-starting helical grooves on drag reduction of smooth and rough circular cylinders in uniform cross flow. In total, four cylinders were tested including smooth and rough cylinders with and without helical grooves.

Flow-Induced Forces on a Cylinder for Different Wall Confinements at High Reynolds Numbers (3.5×105)

1975 ◽  
Vol 97 (2) ◽  
pp. 110-117
Author(s):  
P. Y. Chen ◽  
P. E. Doepker
Keyword(s):  
Flow Velocity ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Interference Effects ◽  
High Reynolds Numbers ◽  
Gap Flow ◽  
High Reynolds ◽  
Flow Medium ◽  
Available Information

The nearness of a cylinder to a wall has an important effect on the flow-induced forces exerted on that cylinder, particularly when the cylinder is relatively large compared to the cross section of the flow channel. This paper describes an investigation of wall interference effects that occur when crossflow-induced forces are exerted on circular cylinders with moderately large blockages (d/h = 0.2 to 0.33) at high Reynolds numbers (3.5 × 105 – 1.2 × 106). The results show that, within the range studied, the gap flow velocity is the correct flow velocity to compensate for wall interference effects. The data reported here represent the first available information on experimental cross-flow-induced forces at such high Reynolds numbers using water as a flow medium.

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