Strouhal numbers of rectangular cylinders

1982 ◽  
Vol 123 ◽  
pp. 379-398 ◽  
Author(s):  
Atsushi Okajima
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Velocity Distribution ◽  
Flow Pattern ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Water Tank ◽  
Height Ratio ◽  
Rectangular Cylinders ◽  
Good Agreement

Experiments on the vortex-shedding frequencies of various rectangular cylinders were conducted in a wind tunnel and in a water tank. The results show how Strouhal number varies with a width-to-height ratio of the cylinders in the range of Reynolds number between 70 and 2 × l04. There is found to exist a certain range of Reynolds number for the cylinders with the width-to-height ratios of 2 and 3 where flow pattern abruptly changes with a sudden discontinuity in Strouhal number. The changes in flow pattern corresponding to the discontinuity of Strouhal number have been confirmed by means of measurements of velocity distribution and flow visualization. These data are compared with those of other investigators. The experimental results have been found to show a good agreement with those of numerical calculations.

Onset of Vortex Shedding in a Periodic Array of Circular Cylinders

2006 ◽  
Vol 128 (5) ◽  
pp. 1101-1105 ◽  
Author(s):  
L. Zhang ◽  
S. Balachandar
Keyword(s):  
Reynolds Number ◽  
Hopf Bifurcation ◽  
Vortex Shedding ◽  
Critical Reynolds Number ◽  
Base Flow ◽  
Periodic Array ◽  
Circular Cylinders ◽  
Rectangular Cylinders

Hopf bifurcation of steady base flow and onset of vortex shedding over a transverse periodic array of circular cylinders is considered. The influence of transverse spacing on critical Reynolds number is investigated by systematically varying the gap between the cylinders from a small value to large separations. The critical Reynolds number behavior for the periodic array of circular cylinders is compared with the corresponding result for a periodic array of long rectangular cylinders considered in [Balanchandar, S., and Parker, S. J., 2002, “Onset of Vortex Shedding in an Inline and Staggered Array of Rectangular Cylinders,” Phys. Fluids, 14, pp. 3714–3732]. The differences between the two cases are interpreted in terms of differences between their wake profiles.

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.

On vortex shedding from a circular cylinder in the critical Reynolds number régime

1969 ◽  
Vol 37 (3) ◽  
pp. 577-585 ◽  
Author(s):  
P. W. Bearman
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Critical Reynolds Number ◽  
Narrow Band ◽  
Critical Regime ◽  
Number Range ◽  
Velocity Fluctuations ◽  
Reynolds Number Range

The flow around a circular cylinder has been examined over the Reynolds number range 105 to 7·5 × 105, Reynolds number being based on cylinder diameter. Narrow-band vortex shedding has been observed up to a Reynolds number of 5·5 × 105, i.e. well into the critical régime. At this Reynolds number the Strouhal number reached the unusually high value of 0·46. Spectra of the velocity fluctuations measured in the wake are presented for several values of Reynolds number.

Vortex Shedding From Struts in an Annular Exhaust Diffuser

1998 ◽  
Vol 120 (1) ◽  
pp. 186-192 ◽  
Author(s):  
T. F. Fric ◽  
R. Villarreal ◽  
R. O. Auer ◽  
M. L. James ◽  
D. Ozgur ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Gas Turbine ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Scale Model ◽  
Bluff Bodies ◽  
Cylinder Wake ◽  
Wind Tunnel Tests ◽  
Full Speed ◽  
Inlet Swirl

Results from scale-model experiments and industrial gas turbine tests show that strut vortex shedding in an annular exhaust diffuser can effectively be modified by adding tapered chord to the struts. The struts are bluff bodies at full-speed, no-load conditions, when inlet swirl is close to 60 deg. Data from wind tunnel tests show that wake Strouhal number is 0.47, larger than that expected for an isolated cylinder wake. This value of Strouhal number agrees with those measured in full-scale exhaust diffusers. Wind tunnel tests showed that a strut with tapered chord most effectively reduced wake amplitudes and shifted shedding frequency. The tapered strut was also effective in reducing shedding amplitude in a scale-model diffuser. Finally, gas turbine tests employing a tapered strut showed significant reductions in unsteady pressure and noise. A major benefit of strut taper is a reduction of noise by uncoupling of vortex shedding from acoustic resonant response.

scholarly journals The onset of unsteadiness of two-dimensional bodies falling or rising freely in a viscous fluid: a linear study

2011 ◽  
Vol 690 ◽  
pp. 173-202 ◽  
Author(s):  
Pauline Assemat ◽  
David Fabre ◽  
Jacques Magnaudet
Keyword(s):  
Reynolds Number ◽  
Viscous Fluid ◽  
Strouhal Number ◽  
Cross Section ◽  
Vortex Shedding ◽  
The Body ◽  
Mode Switching ◽  
Two Dimensional ◽  
Body Dynamics ◽  
Mass Ratios

AbstractWe consider the transition between the steady vertical path and the oscillatory path of two-dimensional bodies moving under the effect of buoyancy in a viscous fluid. Linearization of the Navier–Stokes equations governing the flow past the body and of Newton’s equations governing the body dynamics leads to an eigenvalue problem, which is solved numerically. Three different body geometries are then examined in detail, namely a quasi-infinitely thin plate, a plate of rectangular cross-section with an aspect ratio of 8, and a rod with a square cross-section. Two kinds of eigenmodes are observed in the limit of large body-to-fluid mass ratios, namely ‘fluid’ modes identical to those found in the wake of a fixed body, which are responsible for the onset of vortex shedding, and four additional ‘aerodynamic’ modes associated with much longer time scales, which are also predicted using a quasi-static model introduced in a companion paper. The stability thresholds are computed and the nature of the corresponding eigenmodes is investigated throughout the whole possible range of mass ratios. For thin bodies such as a flat plate, the Reynolds number characterizing the threshold of the first instability and the associated Strouhal number are observed to be comparable with those of the corresponding fixed body. Other modes are found to become unstable at larger Reynolds numbers, and complicated branch crossings leading to mode switching are observed. On the other hand, for bluff bodies such as a square rod, two unstable modes are detected in the range of Reynolds number corresponding to wake destabilization. For large enough mass ratios, the leading mode is similar to the vortex shedding mode past a fixed body, while for smaller mass ratios it is of a different nature, with a Strouhal number about half that of the vortex shedding mode and a stronger coupling with the body dynamics.

Effect of Free-Stream Turbulence on Characteristics of Fluctuating Forces Acting on Two Square Prisms in Tandem Arrangement

1988 ◽  
Vol 110 (2) ◽  
pp. 140-146 ◽  
Author(s):  
H. Sakamoto ◽  
H. Haniu
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Turbulence Intensity ◽  
Vortex Shedding ◽  
Free Stream ◽  
Switching Frequency ◽  
Tandem Arrangement ◽  
Free Stream Turbulence ◽  
Fluid Forces ◽  
Bistable Flow

The effect of the addition of the turbulence intensity to the free stream on the characteristics of the bistable flow which takes place around two square prisms in tandem arrangement was studied experimentally at a Reynolds number of 3.32 × 104. A method of obtaining the fluid forces acting on two prisms in the bistable flow regimes where two flow patterns appear intermittently was introduced, and then the characteristics of the fluid forces, the Strouhal number, and the switching frequency of the switch phenomenon with the variation of the freestream turbulence intensity were investigated. Furthermore, the behavior of the fluid forces and the vortex shedding for other spacings between the two prisms were presented for the variation of the turbulence intensity.

A Study on Vortex Shedding From Spheres in a Uniform Flow

1990 ◽  
Vol 112 (4) ◽  
pp. 386-392 ◽  
Author(s):  
H. Sakamoto ◽  
H. Haniu
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Water Channel ◽  
Reynolds Numbers ◽  
Uniform Flow ◽  
Freestream Velocity ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Visualization Experiments

Vortex shedding from spheres at Reynolds numbers from 3 × 102 to 4 × 104 in a uniform flow was investigated experimentally. Standard hot-wire technique were used to measure the vortex shedding frequency from spheres in a low-speed wind tunnel. Flow-visualization experiments were carried out in a water channel. Important results from the investigation were that (i) the variation of the Strouhal number St (=fD/U0, U0: freestream velocity, D: diameter of the sphere, f: vortex shedding frequency) with the Reynolds number (= U0D/v, v: kinematic viscosity) can be classified into four regions, (ii) the Reynolds number at which the hairpinshaped vortices begin to change from laminar to turbulent vortices so that the wake structure behind the sphere is not shown clearly when a Reynolds number of about 800 is reached, and (vi) at Reynolds numbers ranging from 8X102 to 1.5X104, the higher and lower frequency modes of the Strouhal number coexist.

Numerical Simulation of the Wind Load on the Mast at Different Wind Angles

2014 ◽  
Vol 580-583 ◽  
pp. 3089-3092
Author(s):  
Rong Sheng Cao ◽  
Yuan Yuan Fang ◽  
Ling Wang
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Side Wall ◽  
Reynolds Numbers ◽  
Wind Load ◽  
Large Reynolds Number ◽  
Vertical Force ◽  
Important Impact

The wind load acted on ship mast at different wind angles of large Reynolds number is numerically simulated in this paper. CFX software was used to analyze the trend of constant and fluctuating forces that the mast surface suffered at different Reynolds numbers.The vortex shedding strength of the wind load around the mast was also analyzed according to the trend of Strouhal number varing with the simulated Reynolds numbers. The results show that the wind angle has an important impact on the lift, drag, and vertical force of the mast. The vertical force of the inclined side wall on the mast can not be ignored,and the angle of direction wind has great impact on the Strouhal number at different Reynolds numbers.

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