A numerical study of flow past a rotating circular cylinder using a hybrid vortex scheme

1995 ◽  
Vol 299 ◽  
pp. 35-71 ◽  
Author(s):  
Y. T. Chew ◽  
M. Cheng ◽  
S. C. Luo
Keyword(s):  
Shear Stress ◽  
Circular Cylinder ◽  
Flow Field ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Vortex Method ◽  
Cell Method ◽  
Karman Vortex ◽  
The Mean ◽  
Lift And Drag

The vortex shedding and wake development of a two-dimensional viscous incompressible flow generated by a circular cylinder which begins its rotation and translation impulsively in a stationary fluid is investigated by a hybrid vortex scheme at a Reynolds number of 1000. The rotational to translational speed ratio α varies from 0 to 6. The method used to calculate the flow can be considered as a combination of the diffusion-vortex method and the vortex-in-cell method. More specifically, the full flow field is divided into two regions: near the body surface the diffusion-vortex method is used to solve the Navier–Stokes equations, while the vortex-in-cell method is used in the exterior inviscid domain. Being more efficient, the present computation scheme is capable of extending the computation to a much larger dimensionless time than those reported in the literature.The time-dependent pressure, shear stress and velocity distributions, the Strouhal number of vortex shedding as well as the mean lift, drag, moment and power coefficients are determined together with the streamline and vorticity flow patterns. When comparison is possible, the present computations are found to compare favourably with published experimental and numerical results. The present results seem to indicate the existence of a critical α value of about 2 when a closed streamline circulating around the cylinder begins to appear. Below this critical α, Kármán vortex shedding exists, separation points can be found, the mean lift and drag coefficients and Strouhal number increase almost linearly with α. Above α ≈ 2, the region enclosed by the dividing closed streamline grows in size, Kármán vortex shedding ceases, the flow structure, pressure and shear stress distributions around the cylinder tend towards self-similarity with increase α, and lift and drag coefficients approach asymptotic values. The optimum lift to drag ratio occurs at α ≈ 2. The present investigation confirms Prandtl's postulation of the presence of limiting lift force at high α, and thus the usefulness of the Magnus effect in lift generation is limited.The results show that the present method can be used to calculate not only the global characteristics of the separated flow, but also the precise evolution with time of the fine structure of the flow field.

Fluctuating forces on a rigid circular cylinder in confined flow

1976 ◽  
Vol 78 (3) ◽  
pp. 561-576 ◽  
Author(s):  
A. Richter ◽  
E. Naudascher
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Critical Value ◽  
Experimental Information ◽  
Rectangular Duct ◽  
Wide Range ◽  
Confined Flow ◽  
The Mean ◽  
Lift And Drag

The fluctuating lift and drag acting on a long, rigidly supported circular cylinder placed symmetrically in a narrow rectangular duct were investigated for various blockage percentages over a wide range of Reynolds numbers around the critical value. The data obtained permit a full assessment of the effect of confinement on the mean-drag coefficient, the root-mean-square values of both the drag and the lift fluctuations, the Strouhal number of the dominant vortex shedding, and the Reynolds number marking transition from laminar to turbulent flow separation. Besides experimental information on a subject on which little is known so far, the paper provides a basis for the deduction of better correction procedures concerning the effects of blockage.

scholarly journals Control and Suppression of Vortex Shedding from a Slightly Rough Circular Cylinder by a Discrete Vortex Method

Energies ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 4481 ◽  
Author(s):  
Marcos André de Oliveira ◽  
Paulo Guimarães de Moraes ◽  
Crystianne Lilian de Andrade ◽  
Alex Mendonça Bimbato ◽  
Luiz Antonio Alcântara Pereira
Keyword(s):  
Circular Cylinder ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Vortex Method ◽  
Control Technique ◽  
Saturation State ◽  
Discrete Vortex ◽  
Discrete Vortex Method ◽  
Moving Wall ◽  
History Of

A discrete vortex method is implemented with a hybrid control technique of vortex shedding to solve the problem of the two-dimensional flow past a slightly rough circular cylinder in the vicinity of a moving wall. In the present approach, the passive control technique is inspired on the fundamental principle of surface roughness, promoting modifications on the cylinder geometry to affect the vortex shedding formation. A relative roughness size of ε*/d* = 0.001 (ε* is the average roughness and d* is the outer cylinder diameter) is chosen for the test cases. On the other hand, the active control technique uses a wall plane, which runs at the same speed as the free stream velocity to contribute with external energy affecting the fluid flow. The gap-to-diameter varies in the range from h*/d* = 0.05 to 0.80 (h* is the gap between the moving wall and the cylinder bottom). A detailed account of the time history of pressure distributions, simultaneously investigated with the time evolution of forces, Strouhal number behavior, and boundary layer separation are reported at upper-subcritical Reynolds number flows of Re = 1.0 × 105. The saturation state of the numerical simulations is demonstrated through the analysis of the Strouhal number behavior obtained from temporal history of the aerodynamic loads. The present work provides an improvement in the prediction of Strouhal number than other studies no using roughness model. The aerodynamic characteristics of the cylinder, as well as the control of intermittence and complete interruption of von Kármán-type vortex shedding have been better clarified.

Synchronized Vibrations of a Circular Cylinder in Cross Flow at Supercritical Reynolds Numbers1

2003 ◽  
Vol 125 (1) ◽  
pp. 97-108 ◽  
Author(s):  
Tsutomu Kawamura ◽  
Toshitsugu Nakao ◽  
Masanori Takahashi ◽  
Masaaki Hayashi ◽  
Kouichi Murayama ◽  
...  
Keyword(s):  
Circular Cylinder ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Excited Vibration ◽  
Karman Vortex ◽  
Lock In

Synchronized vibrations of a circular cylinder in a water cross flow at supercritical Reynolds numbers were measured. Turbulence intensities were varied to investigate the effect of the Strouhal number on the synchronization range. Self-excited vibration in the drag direction due to symmetrical vortex shedding began only when the Strouhal number was about 0.29, at a reduced velocity of 1.1. The reduced velocities at the beginning of lock-in vibrations caused by Karman vortex shedding decreased from 1.5 to 1.1 in the drag direction and from 2.7 to 2.2 in the lift direction, as the Strouhal number increased from 0.29 to 0.48.

Vortex-Shedding From Various Yawed Tandem Circular Cylinder Arrangements

2012 ◽  
Author(s):  
Stephen J. Wilkins ◽  
Joseph W. Hall
Keyword(s):  
Experimental Investigation ◽  
Circular Cylinder ◽  
Flow Field ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Pressure Fluctuations ◽  
Cylinder Wall ◽  
Pressure Measurements ◽  
Mean Flow ◽  
The Mean

The struts of a landing gear can be modeled as a tandem cylinder system where one cylinder is yawed to the mean flow direction. The current experimental investigation will examine the effect that yawing either the front or rear cylinder will have on the pressure fluctuations and associated unsteady flow field. This will be accomplished using 24 simultaneous unsteady wall pressure measurements on the cylinder wall. Two yaw angles will be examined here, α = 80° and α = 60°, for both the yawed upstream and yawed downstream cases.

Numerical Simulation of Rivulet Dynamics Associated With Rain-Wind Induced Vibration

2010 ◽  
Author(s):  
Ian J. Taylor ◽  
Andrew C. Robertson
Keyword(s):  
Flow Field ◽  
Thin Liquid Film ◽  
Vortex Method ◽  
The Body ◽  
Wind Loading ◽  
External Loading ◽  
Discrete Vortex ◽  
Unsteady Aerodynamic ◽  
Karman Vortex ◽  
Wind Induced Vibration

On wet and windy days, the inclined cables of cable-stayed bridges can experience large amplitude, potentially damaging oscillations known as Rain-Wind Induced Vibration (RWIV). The phenomenon is believed to be the result of a complicated nonlinear interaction between rivulets of rain water that run down the cables and the wind loading on the cables due to the unsteady aerodynamic flow field. A numerical method has been developed at the University of Strathclyde, to simulate aspects of RWIV, the results of which can be used to assess the importance of the water rivulets on the instability. This combines a Discrete Vortex Method solver to determine the external flow field and unsteady aerodynamic loading and a pseudo-spectral solver based on lubrication theory to model the water on the surface of the body and which is used to determine the evolution and growth of the water rivulets under external loading. These two models are coupled to simulate the interaction between the aerodynamic field and the thin liquid film on a horizontal circular cylinder. The results illustrate the effects of various loading combinations, and importantly demonstrate rivulet formation in the range of angles previous research has indicated that these may suppress the Karman vortex and lead to a galloping instability. These rivulets are found to be of self limiting thickness in all cases.

An Investigation of Flow Fields Over Multi-Element Aerofoils

2001 ◽  
Vol 124 (1) ◽  
pp. 154-165 ◽  
Author(s):  
S. R. Maddah ◽  
H. H. Bruun
Keyword(s):  
Flow Field ◽  
Computational Study ◽  
Separated Flow ◽  
Mean Flow ◽  
Model Configuration ◽  
Attached Flow ◽  
The Mean ◽  
Flap Deflection ◽  
Comparative Results ◽  
Lift And Drag

This paper presents results obtained from a combined experimental and computational study of the flow field over a multi-element aerofoil with and without an advanced slat. Detailed measurements of the mean flow and turbulent quantities over a multi-element aerofoil model in a wind tunnel have been carried out using stationary and flying hot-wire (FHW) probes. The model configuration which spans the test section 600mm×600mm, is made of three parts: 1) an advanced (heel-less) slat, 2) a NACA 4412 main aerofoil and 3) a NACA 4415 flap. The chord lengths of the elements were 38, 250 and 83 mm, respectively. The results were obtained at a chord Reynolds number of 3×105 and a free Mach number of less than 0.1. The variations in the flow field are explained with reference to three distinct flow field regimes: attached flow, intermittent separated flow, and separated flow. Initial comparative results are presented for the single main aerofoil and the main aerofoil with a nondeflected flap at angles of attacks of 5, 10, and 15 deg. This is followed by the results for the three-element aerofoil with emphasis on the slat performance at angles of attack α=10, 15, 20, and 25 deg. Results are discussed both for a nondeflected flap δf=0deg and a deflected flap δf=25deg. The measurements presented are combined with other related aerofoil measurements to explain the main interaction of the slat/main aerofoil and main aerofoil/flap both for nondeflected and deflected flap conditions. These results are linked to numerically calculated variations in lift and drag coefficients with angle of attack and flap deflection angle.

Experimental Investigation of a Tandem Cylinder System With a Yawed Upstream Cylinder

2011 ◽  
Author(s):  
Stephen J. Wilkins ◽  
Joseph W. Hall
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Unsteady Flow ◽  
Surface Pressure ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Pressure Fluctuations ◽  
Mean Flow ◽  
The Mean ◽  
Velocity Spectra

The unsteady flow field produced by a tandem cylinder system with the upstream cylinder yawed to the mean flow direction is investigated for upstream cylinder yaw angles from α = 60° to α = 90°. Multi-point fluctuating surface pressure and hotwire measurements were conducted at various spanwise positions on both the upstream and downstream cylinders. The results indicate that yawing the front cylinder to the mean flow direction causes the pressure and velocity spectra on the upstream and downstream cylinders to become more broadband than for a regular tandem cylinder system, and reduces the magnitude of the peak associated with the vortex-shedding. However, span-wise correlation and coherence measurements indicate that the vortex-shedding is still present and was being obscured by the enhanced three-dimensionality that the upstream yawed cylinder caused and was still present and correlated from front to back, at least for the larger yaw angles investigated. When the cylinder was yawed to α = 60°, the pressure fluctuations became extremely broadband and exhibited shorter spanwise correlation.

Numerical Simulation of Vortex Shedding Past a Circular Cylinder in a Cross-Flow at Low Reynolds Number With Finite Volume-Technique: Part 1 — Forced Oscillations

2007 ◽  
Author(s):  
Antoine Placzek ◽  
Jean-Franc¸ois Sigrist ◽  
Aziz Hamdouni
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Circular Cylinder ◽  
Finite Volume ◽  
Vortex Shedding ◽  
Stokes Equations ◽  
Cross Flow ◽  
Forced Oscillations ◽  
Lift And Drag ◽  
Wake Characteristics

The numerical simulation of the flow past a circular cylinder forced to oscillate transversely to the incident stream is presented here for a fixed Reynolds number equal to 100. The 2D Navier-Stokes equations are solved with a classical Finite Volume Method with an industrial CFD code which has been coupled with a user subroutine to obtain an explicit staggered procedure providing the cylinder displacement. A preliminary work is conducted in order to check the computation of the wake characteristics for Reynolds numbers smaller than 150. The Strouhal frequency fS, the lift and drag coefficients CL and CD are thus controlled among other parameters. The simulations are then performed with forced oscillations f0 for different frequency rations F = f0/fS in [0.50–1.50] and an amplitude A varying between 0.25 and 1.25. The wake characteristics are analysed using the time series of the fluctuating aerodynamic coefficients and their FFT. The frequency content is then linked to the shape of the phase portrait and to the vortex shedding mode. By choosing interesting couples (A,F), different vortex shedding modes have been observed, which are similar to those of the Williamson-Roshko map.

Experimental Investigation of Uniform-Shear Flow Past a Circular Cylinder

1992 ◽  
Vol 114 (3) ◽  
pp. 457-460 ◽  
Author(s):  
Tae Soon Kwon ◽  
Hyung Jin Sung ◽  
Jae Min Hyun
Keyword(s):  
Circular Cylinder ◽  
Shear Flow ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Laboratory Experiments ◽  
Processing Technique ◽  
Image Processing Technique ◽  
Uniform Shear ◽  
Uniform Shear Flow ◽  
Shear Parameter

Extensive laboratory experiments were carried out to investigate the uniform-shear flow approaching a circular cylinder. The aim was to present the Strouhal number (St)- Reynolds number (Re) diagrams over a broad range of the shear parameter K (0 ≤ K ≤ 0.25) and at higher values of Re (600 ≤ Re ≤ 1600). An image processing technique, in conjunction with flow visualization studies, was used to secure more quantitative depictions of vortex shedding from the cylinder. The Strouhal number increases with increasing shear parameter. The drag coefficient decreases with increasing Re; also, Cd decreases as the shear parameter K increases.

721 Effects of Helical Strakes on Karman Vortex Shedding from a Circular Cylinder with Serrated Fin

2004 ◽  
Vol 2004 (0) ◽  
pp. _721-1_-_721-5_
Author(s):  
Hiromitsu HAMAKAWA ◽  
Tohru FUKANO ◽  
Masaki ANDO ◽  
Eiichi NISHIDA
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Helical Strakes ◽  
Karman Vortex
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