A Numerical Investigation of the Effects of Flow Pulsations on the Drag Force Over a Cylinder

The Mean ◽

Flow over a cylinder is a fundamental fluid mechanics problem that involves a simple geometry, yet increasingly complex flow patterns as the Reynolds number is increased, most notably the development of a Karman vortex with a natural vortex shedding frequency fs when the Reynolds number exceeds a value of about 40. The goal of this ongoing study is to numerically investigate the effect of an incoming free-stream velocity pulsation with a mean Reynolds number of 100 on the drag force over and vorticity dynamics behind a circular cylinder. This paper reports on initial results involving unsteady, laminar and incompressible flows over a circular cylinder. Sinusoidal free-stream pulsations with amplitudes Av varying between 25% and 75% of the mean free-stream velocity and frequencies f varying between 0.25 and 5 times the natural shedding frequency were considered. Of particular interest to us is the interaction between the pulsating frequency and natural vortex shedding frequency and the resulting effects on drag. Interestingly, at frequencies close to the natural frequency, and to twice the natural frequency, a sudden drop in the mean value of the drag coefficient is observed. This drop in the drag coefficient is also accompanied by a change in the flow and vortex shedding patterns observed behind the cylinder.

Volume 6: Fluids and Thermal Systems; Advances for Process Industries, Parts A and B ◽

A Numerical Investigation of the Effects of Flow Pulsations on the Vortex Shedding, Drag and Lift Forces Over a Cylinder

10.1115/imece2011-62276 ◽

2011 ◽

Author(s):

Eric D’herde ◽

Laila Guessous

Keyword(s):

Reynolds Number ◽

Circular Cylinder ◽

Vortex Shedding ◽

Free Stream ◽

Lift Coefficient ◽

Stream Velocity ◽

The Mean ◽

Shedding Frequency ◽

Drag And Lift

Flow over a cylinder is a fundamental fluid mechanics problem that involves a simple geometry, yet increasingly complex flow patterns as the Reynolds number is increased, most notably the development of a Karman vortex with a natural vortex shedding frequency when the Reynolds number exceeds a value of about 40. The goal of this ongoing study is to numerically investigate the effect of an incoming free-stream velocity pulsation with a mean Reynolds number of 100 on the drag and lift forces over and vorticity dynamics behind a circular cylinder. This paper reports on initial results involving unsteady, laminar and incompressible flows over a circular cylinder. Sinusoidal free-stream pulsations with amplitudes Av varying between 25% and 75% of the mean free-stream velocity and frequencies varying between 0.25 and 5 times the natural shedding frequency fs were considered. Of particular interest to us is the interaction between the pulsating frequency and natural vortex shedding frequency and the resulting effects on drag. Interestingly, at frequencies close to the natural frequency, and to twice the natural frequency, a sudden drop in the mean value of the drag coefficient is observed. The first drop in the drag coefficient, i.e. near f = fs, is also accompanied by a change in the flow and vortex shedding patterns observed behind the cylinder. This change in vortex shedding pattern manifests itself as a departure from symmetrical shedding, and in a non-zero mean lift coefficient value. The second drop, i.e. near f = 2 fs, has similar characteristics, except that the mean lift coefficient remains at zero.

Vortex shedding from a rectangular prism and a circular cylinder placed vertically in a turbulent boundary layer

10.1017/s0022112083000087 ◽

1983 ◽

Vol 126 ◽

pp. 147-165 ◽

Cited By ~ 159

Author(s):

Hiroshi Sakamoto ◽

Mikio Arie

Keyword(s):

Boundary Layer ◽

Aspect Ratio ◽

Circular Cylinder ◽

Turbulent Boundary Layer ◽

Vortex Shedding ◽

Rectangular Prism ◽

Stream Velocity ◽

Shedding Frequency ◽

Two Bodies

Measurements of the vortex-shedding frequency behind a vertical rectangular prism and a vertical circular cylinder attached to a plane wall are correlated with the characteristics of the smooth-wall turbulent boundary layer in which they are immersed. Experimental data were collected to investigate the effects of (i) the aspect ratio of these bodies and (ii) the boundary-layer characteristics on the vortex-shedding frequency. The Strouhal number for the rectangular prism and the circular cylinder, defined by S = fcw/U0 and fcd/U0 respectively, was found to be expressed by a power function of the aspect ratio h/w (or h/d). Here fc is the vortex-shedding frequency, U0 is the free-stream velocity, h is the height, w is the width and d is the diameter. As the aspect ratio is reduced, the type of vortex shedding behind each of the two bodies was found to change from the Karman-type vortex to the arch-type vortex at the aspect ratio of 2·0 for the rectangular prism and 2·5 for the circular cylinder.

Flow-Induced Vibration of a Cylinder in the Wake of Another of Smaller Diameter

Volume 4: Fluid-Structure Interaction ◽

10.1115/pvp2014-28086 ◽

2014 ◽

Author(s):

Md. Mahbub Alam ◽

An Ran ◽

Yu Zhou

Keyword(s):

Circular Cylinder ◽

Free Stream ◽

Cross Flow ◽

Induced Response ◽

Stream Velocity ◽

Flow Induced Vibration ◽

Cylinder Diameter ◽

Spacing Ratio ◽

This paper presents cross-flow induced response of a both-end-spring-mounted circular cylinder (diameter D) placed in the wake of a rigid circular cylinder of smaller diameter d. The cylinder vibration is constrained to the transverse direction. The cylinder diameter ratio d/D and spacing ratio L/d are varied from 0.2 to 1.0 and 1.0 to 5.5, respectively, where L is the distance between the center of the upstream cylinder to the forward stagnation point of the downstream cylinder. A violent vibration of the cylinder is observed for d/D = 0.2 ∼ 0.8 at L/d = 1.0, for d/D = 0.24 ∼ 0.6 at 1.0 < L/d ≤ 2.5, for d/D = 0.2 ∼ 0.4 at 2.5 < L/d ≤ 3.5, and for d/D = 0.2 at 3.5 < L/d ≤ 5.5, but not for d/D = 1.0. A smaller d/D generates vibration for a longer range of L/d. The violent vibration occurs at a reduced velocity Ur (=U∞/fnD, where U∞ is the free-stream velocity and fn the natural frequency of the cylinder system) beyond the vortex excitation regime (Ur ≥ 8) depending on d/D and L/d. Once the vibration starts to occur, the vibration amplitude increases rapidly with increasing Ur. It is further noted that the flow behind the downstream cylinder is characterized by two predominant frequencies, corresponding to the cylinder vibration frequency and the natural vortex shedding frequency of the cylinder, respectively. While the former persists downstream, the latter vanishes rapidly.

The locking-on of vortex shedding due to the cross-stream vibration of circular cylinders in uniform and shear flows

10.1017/s0022112076001985 ◽

1976 ◽

Vol 74 (4) ◽

pp. 641-665 ◽

Cited By ~ 122

Author(s):

P. K. Stansby

Keyword(s):

Reynolds Number ◽

Shear Flow ◽

Vortex Shedding ◽

Shear Flows ◽

Uniform Flow ◽

Circular Cylinders ◽

Stream Velocity ◽

Shedding Frequency ◽

The Cross

The frequencies of vortex shedding from circular cylinders forced to oscillate transversely in low-turbulence uniform and shear flows were investigated. The stream velocity in the shear flow varied linearly with spanwise distance.In both flows the vortex shedding frequency locked on to the cylinder frequency and to submultiples of the cylinder frequency. In uniform flow the range of cylinder frequencies for locking-on was dependent on the amplitude of oscillation and Reynolds number. At the boundaries of locking-on at the cylinder frequency locked-on shedding was intermittent with unforced shedding and locking-on was accompanied by a change in wake width. At a particular cylinder frequency near mid-range it is conjectured that the wake width jumped from being greater to being less than that for the stationary cylinder. In shear flow the spanwise extent of locking-on at the cylinder frequency was explained by considering the uniform flow results and the inclination of shed vortices in shear flow. At the spanwise boundaries of this locking-on, locked-on cells were shed intermittently with unforced cells which were more stable in frequency than the corresponding cells for the stationary cylinder.

Vortex-Induced Vibration for Heat Transfer Enhancement

Volume 8A: Heat Transfer and Thermal Engineering ◽

10.1115/imece2014-37594 ◽

2014 ◽

Author(s):

Junxiang Shi ◽

Steven R. Schafer ◽

Chung-Lung (C. L. ) Chen

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Heat Transfer Enhancement ◽

Natural Frequency ◽

Vortex Shedding ◽

Pressure Loss ◽

Thermal Boundary Layer ◽

Transfer Enhancement ◽

A passive, self-agitating method which takes advantage of vortex-induced vibration (VIV) is presented to disrupt the thermal boundary layer and thereby enhance the convective heat transfer performance of a channel. A flexible cylinder is placed at centerline of a channel. The vortex shedding due to the presence of the cylinder generates a periodic lift force and the consequent vibration of the cylinder. The fluid-structure-interaction (FSI) due to the vibration strengthens the disruption of the thermal boundary layer by reinforcing vortex interaction with the walls, and improves the mixing process. This novel concept is demonstrated by a three-dimensional modeling study in different channels. The fluid dynamics and thermal performance are discussed in terms of the vortex dynamics, disruption of the thermal boundary layer, local and average Nusselt numbers (Nu), and pressure loss. At different conditions (Reynolds numbers, channel geometries, material properties), the channel with the VIV is seen to significantly increase the convective heat transfer coefficient. When the Reynolds number is 168, the channel with the VIV improves the average Nu by 234.8% and 51.4% in comparison with a clean channel and a channel with a stationary cylinder, respectively. The cylinder with the natural frequency close to the vortex shedding frequency is proved to have the maximum heat transfer enhancement. When the natural frequency is different from the vortex shedding frequency, the lower natural frequency shows a higher heat transfer rate and lower pressure loss than the larger one.

Experiments on the flow past an inclined disk

10.1017/s0022112067001120 ◽

1967 ◽

Vol 29 (4) ◽

pp. 691-703 ◽

Cited By ~ 30

Author(s):

J. R. Calvert

Keyword(s):

Vortex Shedding ◽

Free Stream ◽

Stream Velocity ◽

Length Scale ◽

Angle Of Incidence ◽

Axially Symmetric ◽

Periodic Motions ◽

Reference Velocity ◽

Shedding Frequency ◽

A Chain

The wake of a disk at an angle to a stream contains marked periodic motions which arise from the regular shedding of vortices from the trailing edge. The vortices are in the form of a chain of irregular rings, each one linked to the succeeding one, and they move downstream at about 0·6 of free-stream velocity. The prominence of the vortex shedding increases as the angle of incidence (measured from the normal) increases up to at least 50°. The shedding frequency increases with the angle of incidence, but by a suitable choice of reference velocity and length scale, may be described by a wake Strouhal number which has the constant value 0·21 for all angles of incidence above zero, up to at least 40°.Axially-symmetric bodies at zero incidence shed vortices in a similar manner, except that the orientation of the plane of vortex shedding is not fixed and varies from time to time.

Laminar Forced Convection From a Circular Cylinder Placed in a Micropolar Fluid

Journal of Heat Transfer ◽

10.1115/1.2426360 ◽

2006 ◽

Vol 129 (3) ◽

pp. 256-264 ◽

Cited By ~ 2

Author(s):

F. M. Mahfouz

Keyword(s):

Reynolds Number ◽

Circular Cylinder ◽

Prandtl Number ◽

Drag Coefficient ◽

Forced Convection ◽

Vortex Shedding ◽

Micropolar Fluid ◽

Clear Trend ◽

Thermal Fields ◽

Laminar Forced Convection

In this paper laminar forced convection associated with the cross-flow of micropolar fluid over a horizontal heated circular cylinder is investigated. The conservation equations of mass, linear momentum, angular momentum and energy are solved to give the details of flow and thermal fields. The flow and thermal fields are mainly influenced by Reynolds number, Prandtl number and material parameters of micropolar fluid. The Reynolds number is considered up to 200 while the Prandtl number is fixed at 0.7. The dimensionless vortex viscosity is the only material parameter considered in this study and is selected in the range from 0 to 5. The study has shown that generally the mean heat transfer decreases as the vortex viscosity increases. The results have also shown that both the natural frequency of vortex shedding and the amplitude of oscillating lift force experience clear reduction as the vortex viscosity increases. Moreover, the study showed that there is a threshold value for vortex viscosity above which the flow over the cylinder never responds to perturbation and stays symmetric without vortex shedding. Regarding drag coefficient, the results have revealed that within the selected range of controlling parameters the drag coefficient does not show a clear trend as the vortex viscosity increases.

Flow past a rotationally oscillating cylinder

10.1017/jfm.2013.469 ◽

2013 ◽

Vol 735 ◽

pp. 307-346 ◽

Cited By ~ 25

Author(s):

S. Kumar ◽

C. Lopez ◽

O. Probst ◽

G. Francisco ◽

D. Askari ◽

...

Keyword(s):

Reynolds Number ◽

Vortex Shedding ◽

Three Dimensional ◽

Far Field ◽

Two Dimensional ◽

Flow Past ◽

Shedding Frequency ◽

Flow Visualizations ◽

Hydrogen Bubble Technique

AbstractFlow past a circular cylinder executing sinusoidal rotary oscillations about its own axis is studied experimentally. The experiments are carried out at a Reynolds number of 185, oscillation amplitudes varying from $\mathrm{\pi} / 8$ to $\mathrm{\pi} $, and at non-dimensional forcing frequencies (ratio of the cylinder oscillation frequency to the vortex-shedding frequency from a stationary cylinder) varying from 0 to 5. The diagnostic is performed by extensive flow visualization using the hydrogen bubble technique, hot-wire anemometry and particle-image velocimetry. The wake structures are related to the velocity spectra at various forcing parameters and downstream distances. It is found that the phenomenon of lock-on occurs in a forcing frequency range which depends not only on the amplitude of oscillation but also the downstream location from the cylinder. The experimentally measured lock-on diagram in the forcing amplitude and frequency plane at various downstream locations ranging from 2 to 23 diameters is presented. The far-field wake decouples, after the lock-on at higher forcing frequencies and behaves more like a regular Bénard–von Kármán vortex street from a stationary cylinder with vortex-shedding frequency mostly lower than that from a stationary cylinder. The dependence of circulation values of the shed vortices on the forcing frequency reveals a decay character independent of forcing amplitude beyond forcing frequency of ${\sim }1. 0$ and a scaling behaviour with forcing amplitude at forcing frequencies ${\leq }1. 0$. The flow visualizations reveal that the far-field wake becomes two-dimensional (planar) near the forcing frequencies where the circulation of the shed vortices becomes maximum and strong three-dimensional flow is generated as mode shape changes in certain forcing parameter conditions. It is also found from flow visualizations that even at higher Reynolds number of 400, forcing the cylinder at forcing amplitudes of $\mathrm{\pi} / 4$ and $\mathrm{\pi} / 2$ can make the flow field two-dimensional at forcing frequencies greater than ${\sim }2. 5$.

Velocity Measurements on the Forward Portion of a Cylinder

Journal of Fluids Engineering ◽

10.1115/1.2909396 ◽

1990 ◽

Vol 112 (2) ◽

pp. 243-245 ◽

Cited By ~ 4

Author(s):

D. E. Paxson ◽

R. E. Mayle

Keyword(s):

Boundary Layer ◽

Laminar Flow ◽

Circular Cylinder ◽

Vortex Shedding ◽

Static Pressure ◽

Free Stream ◽

Stream Velocity ◽

Pressure Measurements ◽

Velocity Measurements ◽

Flow Around A Cylinder

Velocity measurements in the laminar boundary layer around the forward portion of a circular cylinder are presented. These results are compared to Blasius’ theory for laminar flow around a cylinder using a free-stream velocity distribution obtained from static pressure measurements on the cylinder. Even though the flow is periodically unsteady as a result of vortex shedding from the cylinder, it is found that the agreement is excellent.

Flow Around a Normal Plate of Finite Width Immersed in a Turbulent Boundary Layer

Journal of Fluids Engineering ◽

10.1115/1.3240950 ◽

1983 ◽

Vol 105 (1) ◽

pp. 98-104 ◽

Cited By ~ 11

Author(s):

H. Sakamoto ◽

M. Arie

Keyword(s):

Boundary Layer ◽

Aspect Ratio ◽

Turbulent Boundary Layer ◽

Power Function ◽

Vortex Shedding ◽

Stream Velocity ◽

Finite Width ◽

Pressure Drag ◽

An experimental investigation was carried out on the flow around a normal plate of finite width mounted on a smooth plane wall along which a turbulent boundary layer was fully developed. Experimental data were collected to investigate the effects of (1) the aspect ratio of the plate (2) the parameters characterizing the boundary-layer on the pressure drag and the vortex shedding frequency. The pressure drag coefficient of the plate defined by CDτ = D/(1/2ρuτ2hw) was found to be expressed by a power function of huτ/ν in the range h/δ<1.0 for each aspect ratio w/h, where D is the pressure drag, uτ is the shear velocity, ρ is the density of fluid, h and w are the height and the width of the plate, respectively, ν is the kinematic viscosity, δ is the thickness of the boundary layer. Also, the Strouhal number for the plate defined by St =fc • w/ U0 was found to be expressed by a power function of the aspect ratio w/h in the range of h/δ less than about 1.0, where fc is the vortex shedding frequency, U0 is the free-stream velocity. As the aspect ratio was reduced, the type of vortex shedding behind the plate was found to change from the arch type to the Karman type at the aspect ratio of about 0.8.