Fluctuating Lift Forces of the Karman Vortex Streets on Single Circular Cylinders and in Tube Bundles: Part 1—The Vortex Street Geometry of the Single Circular Cylinder

1972 ◽  
Vol 94 (2) ◽  
pp. 603-610 ◽  
Author(s):  
Y. N. Chen
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Vortex Street ◽  
Circular Cylinders ◽  
Number Range ◽  
Pressure Drag ◽  
Minimum Drag ◽  
Vortex Streets ◽  
Karman Vortex ◽  
Better Than

The geometry of the vortex street for single circular cylinders will be calculated from the measured values given by numerous investigators about the steady pressure drag coefficient and the Strouhal number, whereby the Kronauer minimum drag criterion comes into use. The calculated results will be compared with the experimentally determined ones. A good agreement can be achieved between both. The Bearman-Strouhal number SB = fh/Us will also be computed as a function of the Reynolds number. Furthermore a new wake number C = fh2/Γ will be introduced. It will be shown that this new number is universally much better than the Bearman one. It remains constant at 0.165 for an ideal flow over the whole Reynolds number range up to the highest value of 107 ever measured hitherto.

Fluctuating Lift Forces of the Karman Vortex Streets on Single Circular Cylinders and in Tube Bundles: Part 2—Lift Forces of Single Cylinders

1972 ◽  
Vol 94 (2) ◽  
pp. 613-618 ◽  
Author(s):  
Y. N. Chen
Keyword(s):  
Lift Coefficient ◽  
Vortex Street ◽  
Circular Cylinders ◽  
Pressure Drag ◽  
Vortex Streets ◽  
Order Of Magnitude ◽  
Karman Vortex ◽  
Lift Forces ◽  
The Right ◽  
Right Order

The fluctuating lift force of the Karman vortex on a single circular cylinder will be investigated theoretically for an ideal inviscid vortex street with rectilinear vortices. In this investigation the model introduced by von Karman will be used. As a result, the relationship between the fluctuating lift coefficient CL and the characteristic dimensions of the vortex street can be derived. This leads to establishing the equation between the fluctuating lift coefficient CL and the steady pressure drag coefficient CD. Since the curve of the theoretical lift coefficient practically envelops the spreading field of the experimentally determined points, the theory can be considered to be adequate to give the right order of magnitude for the lift of the Karman vortex. It will further be shown, that the spread of the measured values is in connection with the correlation length of the vortex along the cylinder axis.

On vortex street wakes

1967 ◽  
Vol 28 (4) ◽  
pp. 625-641 ◽  
Author(s):  
P. W. Bearman
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Bluff Body ◽  
Vortex Street ◽  
Number Range ◽  
Pressure Drag ◽  
Blunt Trailing Edge ◽  
Splitter Plates ◽  
Base Bleed ◽  
Potential Vortex

The flow in the wake of a two-dimensional blunt-trailing-edge body was investigated in the Reynolds number range, Reynolds number being referred to base height, 1·3 × 104 to 4·1 × 104. The effects of splitter plates and base bleed on the vortex street were examined. Measurements were made of the longitudinal spacing between vortices and the velocity of the vortices, and compared with values predicted by von Kármán's potential vortex street model. The lateral spacing was estimated by using both the von Kármán and Kronauer stability criteria. A new universal wake Strouhal number is devised, using the value of lateral spacing predicted by the Kronauer stability condition as the length dimension. A correlation of bluff-body data was found when pressure drag coefficient times Strouhal number was plotted against base pressure.

A note on vortex streets behind circular cylinders at low Reynolds numbers

1971 ◽  
Vol 45 (1) ◽  
pp. 203-208 ◽  
Author(s):  
D. J. Tritton
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Number Range ◽  
Low Reynolds Numbers ◽  
Current State ◽  
Reynolds Number Range ◽  
Vortex Streets ◽  
Low Reynolds

A discussion is given of the current state of knowledge of vortex streets behind circular cylinders in the Reynolds number range 50 to 160. This was prompted by Gaster's (1969) report that he could not find the transition at a Reynolds number of about 90 observed by Tritton (1959) and Berger (1964a). A further brief experiment confirming the existence of the transition is described Reasons for rejecting Gaster's interpretation are advanced. Possible (mutually alternative) explanations of the discrepant observations are suggested.

Global frequency selection in the observed time-mean wakes of circular cylinders

2008 ◽  
Vol 601 ◽  
pp. 425-441 ◽  
Author(s):  
MOSES KHOR ◽  
JOHN SHERIDAN ◽  
MARK C. THOMPSON ◽  
KERRY HOURIGAN
Keyword(s):  
Reynolds Number ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Linear Instability ◽  
Circular Cylinders ◽  
Near Wake ◽  
Mean Velocity ◽  
Number Range ◽  
Wake Instability ◽  
Karman Vortex

Observations have been made of the time-mean velocity profile at midspan in the near-wake of circular cylinders at moderate Reynolds numbers between 600 and 4600, well beyond the Reynolds number of approximately 200 at which the wake becomes three-dimensional. The measured profiles are found to be represented quite accurately by a family of function profiles with known linear instability characteristics. The complex instability frequency is then determined as a function of wake position, using the function profiles. In general, the near wake undergoes a transition from convective to absolute instability; the distance downstream to the point of transition is found to increase over the Reynolds number range investigated. The emergence of a significant region of convective instability is consistent with the known appearance of Bloor–Gerrard vortices. The selected frequency of the wake instability is determined by the saddle-point criterion; the Strouhal numbers for Bénard–von Kármán vortex shedding are found to compare well with the values in the literature.

Experiments on the flow past a circular cylinder at low Reynolds numbers

1959 ◽  
Vol 6 (4) ◽  
pp. 547-567 ◽  
Author(s):  
D. J. Tritton
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Experimental Evidence ◽  
Theoretical Calculations ◽  
Reynolds Numbers ◽  
Vortex Street ◽  
Circular Cylinders ◽  
Number Range ◽  
Low Reynolds Numbers ◽  
Experimental Values

Part I describes measurements of the drag on circular cylinders, made by observing the bending of quartz fibres, in a stream with the Reynolds number range 0·5-100. Comparisons are made with other experimental values (which cover only the upper part of this range) and with the various theoretical calculations.Part II advances experimental evidence for there being a transition in the mode of the vortex street in the wake of a cylinder at a Reynolds number around 90. Investigations of the nature of this transition and the differences between the flows on either side of it are described. The interpretation that the change is between a vortex street originating in the wake and one originating in the immediate vicinity of the cylinder is suggested.

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.

Computational Fluid Dynamics Study of a Flexible Flapping Hydrofoil Propulsor

2016 ◽  
Author(s):  
Harikrishnan Vijayakumaran ◽  
Parameswaran Krishnankutty
Keyword(s):  
Fluid Dynamics ◽  
Reynolds Number ◽  
Strouhal Number ◽  
Thrust Coefficient ◽  
Number Range ◽  
Wake Field ◽  
Propulsive Performance ◽  
Velocity Magnitude ◽  
Maximum Angle ◽  
Motion Parameters

A CFD study to understand the hydrodynamics and fluid flow around a chordwise flexible hydrofoil with combined sway and yaw motion which imitates the caudal fin flapping in thunniforms, is presented. The dependency of motion parameters of the flexible flapping hydrofoil to its propulsive performance is studied by carrying out the analyses over a Strouhal number range of 0.1 to 0.4 in steps of 0.025 at three maximum angle of attacks viz. 10°,15°,20°. Qualitative observations of the wake field and trailing jet is presented using velocity magnitude contours and vorticity contours. The analyses carried out at 40,000 Reynolds number and sway amplitude of 0.75 chordlength, revealed that the average thrust coefficient increases with increase in Strouhal number and maximum angle of attacks. The highest efficiency is achieved when the maximum angle of attack is 15° and Strouhal number is 0.225.

Simulation of the Wake of the Flow Around Two Side-By-Side Circular Cylinders at Reynolds Number 5000

2019 ◽  
Author(s):  
Anna Lyhne Jensen ◽  
Henrik Sørensen ◽  
Jakob Hærvig
Keyword(s):  
Reynolds Number ◽  
Circular Cylinders ◽  
Eddy Simulation ◽  
Gap Flow ◽  
Large Eddy ◽  
Vortex Streets ◽  
Flow Phenomena ◽  
Pitch Ratio ◽  
Pitch Distance ◽  
Stable Flow

Abstract Interaction between the wakes of two cylinders in side-by-side configuration creates interesting flow phenomena. The nature of the wake depends on the Reynolds number and the transverse pitch distance between the cylinders. The flow over two side-by-side cylinders of equal diameter is simulated in 3D at Reynolds number 5000 using Large Eddy Simulation (LES). The centre-to-centre transverse pitch ratio is varied and the flow behind the cylinders is classified into either a bi-stable flow regime with biased gap flow or a regime with parallel vortex streets. Furthermore, representative instantaneous flow fields, Strouhal number and the time varying drag coefficient C′D are presented.

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