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

1983 ◽  
Vol 105 (1) ◽  
pp. 98-104 ◽  
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 ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

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.

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

1983 ◽  
Vol 126 ◽  
pp. 147-165 ◽  
Author(s):  
Hiroshi Sakamoto ◽  
Mikio Arie
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Circular Cylinder ◽  
Turbulent Boundary Layer ◽  
Vortex Shedding ◽  
Rectangular Prism ◽  
Stream Velocity ◽  
Vortex Shedding Frequency ◽  
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.

The Influence of Boundary Layer Velocity Gradients and Bed Proximity on Vortex Shedding From Free Spanning Pipelines

1984 ◽  
Vol 106 (1) ◽  
pp. 70-78 ◽  
Author(s):  
A. J. Grass ◽  
P. W. J. Raven ◽  
R. J. Stuart ◽  
J. A. Bray
Keyword(s):  
Boundary Layer ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Combined Effects ◽  
Maximum Increase ◽  
Velocity Gradients ◽  
Large Velocity ◽  
Layer Velocity ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The paper summarizes the results of a laboratory study of the separate and combined effects of bed proximity and large velocity gradients on the frequency of vortex shedding from pipeline spans immersed in the thick boundary layers of tidal currents. This investigation forms part of a wider project concerned with the assessment of span stability. The measurements show that in the case of both sheared and uniform approach flows, with and without velocity gradients, respectively, the Strouhal number defining the vortex shedding frequency progressively increases as the gap between the pipe base and the bed is reduced below two pipe diameters. The maximum increase in vortex shedding Strouhal number, recorded close to the bed in an approach flow with large velocity gradients, was of the order of 25 percent.

Vortex-Induced Vibration for Heat Transfer Enhancement

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 ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

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.

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

2011 ◽  
Author(s):  
Eric D’herde ◽  
Laila Guessous
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Natural Frequency ◽  
Vortex Shedding ◽  
Free Stream ◽  
Stream Velocity ◽  
Vortex Shedding Frequency ◽  
The Mean ◽  
Shedding Frequency

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.

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

2011 ◽  
Author(s):  
Eric D’herde ◽  
Laila Guessous
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Free Stream ◽  
Lift Coefficient ◽  
Stream Velocity ◽  
Vortex Shedding Frequency ◽  
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.

scholarly journals Cavitation in Ka´rma´n Vortex Shedding From 2D Hydrofoil: Wall Roughness Effects

2007 ◽  
Author(s):  
Philippe Ausoni ◽  
Mohamed Farhat ◽  
Franc¸ois Avellan
Keyword(s):  
Boundary Layer ◽  
Vortex Shedding ◽  
Leading Edge ◽  
Transition To Turbulence ◽  
Special Focus ◽  
Roughness Effects ◽  
Vortex Induced Vibration ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Layer Flow

The present study deals with the shedding process of the Ka´rma´n vortices in the wake of a NACA0009 hydrofoil at high Reynolds number, Reh = 25·103 − 65·103. This research addresses the effects of the foil leading edge roughness on the wake dynamic with a special focus on the vortex shedding frequency, vortex-induced vibration and three-dimensionality of vortex shedding. For smooth leading edge, the shedding frequency of Ka´rma´n vortices occurs at constant Strouhal number, St = 0.24. The wake exhibits 3D instabilities and the vortex induced vibration signals strong modulation with intermittent weak shedding cycles. Direct relation between vibration amplitude and vortex spanwise organization is shown. In the case of rough leading edge, the Ka´rma´n shedding frequency is notably decreased compared to the smooth one, St = 0.18. Moreover, the vortex induced vibration level is significantly increased and the vibration spectra sharply peaked. The occurrence of vortex dislocations is shown to be less frequent with the roughness. The shedding of the vortices is considered on the whole as in phase along the hydrofoil span. Obviously, the shedding process of the Ka´rma´n vortices is highly related to the state of the boundary layer over the entire hydrofoil. It is believed that in the case of smooth leading edge, slight spanwise non-uniformities in the boundary-layer flow lead to slight instantaneous variation in vortex shedding frequency along the span which is enough to trigger vortex dislocations. On the contrary, for the rough leading edge, the location of transition to turbulence is uniformly forced which leads to the reduction of the spanwise boundary-layer non-uniformities and therefore to the enhancement of the coherence length of the Ka´rma´n vortices.

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

1976 ◽  
Vol 74 (4) ◽  
pp. 641-665 ◽  
Author(s):  
P. K. Stansby
Keyword(s):  
Reynolds Number ◽  
Shear Flow ◽  
Vortex Shedding ◽  
Shear Flows ◽  
Uniform Flow ◽  
Circular Cylinders ◽  
Stream Velocity ◽  
Vortex Shedding Frequency ◽  
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.

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