The effect of buoyancy on vortex shedding in the near wake of a circular cylinder

1990 ◽  
Vol 220 ◽  
pp. 253-266 ◽  
Author(s):  
Keun-Shik Chang ◽  
Jong-Youb Sa
Keyword(s):  
Nusselt Number ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Transport Equation ◽  
Fourth Order ◽  
Vortex Shedding ◽  
Near Wake ◽  
Periodic Flows ◽  
Vortex Pattern ◽  
Vorticity Transport

The phenomenon of vortex shedding from a heated/cooled circular cylinder has been investigated numerically in the mixed natural and forced convection regimes. Accuracy of the computation was achieved by the fourth-order Hermitian relation applied to the contravariant velocity components in the convection terms of the vorticity transport equation, and by the far-boundary stream-function condition of an integral-series form developed by the authors. Purely periodic flows at Re = 100, efficiently established through the use of a direct elliptic solver called the SEVP, was found to degenerate into a steady twin-vortex pattern at the critical Grashof number 1500, confirming an earlier experimental observation identified as ‘breakdown of the Kármán vortex street’. Various other buoyancy effects about the heated/cooled cylinder are discussed by means of the flow patterns, the Nusselt number and the drag coefficient curves.

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

2006 ◽  
Vol 129 (3) ◽  
pp. 256-264 ◽  
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.

On vortex formation from a cylinder. Part 1. The initial instability

1988 ◽  
Vol 190 ◽  
pp. 491-512 ◽  
Author(s):  
M. F. Unal ◽  
D. Rockwell
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
Circular Cylinder ◽  
Shear Layer ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Absolute Instability ◽  
Near Wake ◽  
Lower Range ◽  
Fluctuation Amplitude

Vortex shedding from a circular cylinder is examined over a tenfold range of Reynolds number, 440 ≤ Re ≤ 5040. The shear layer separating from the cylinder shows, to varying degrees, an exponential variation of fluctuating kinetic energy with distance downstream of the cylinder. The characteristics of this unsteady shear layer are interpreted within the context of an absolute instability of the near wake. At the trailing-end of the cylinder, the fluctuation amplitude of the instability correlates well with previously measured values of mean base pressure. Moreover, this amplitude follows the visualized vortex formation length as Reynolds number varies. There is a drastic decrease in this near-wake fluctuation amplitude in the lower range of Reynolds number and a rapid increase at higher Reynolds number. These trends are addressed relative to the present, as well as previous, observations.

Symmetric Vortex Shedding From a Circular Cylinder Under Periodic Flow Forcing

2006 ◽  
Author(s):  
E. Konstantinidis ◽  
S. Balabani
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Excitation Frequency ◽  
Symmetric Mode ◽  
Near Wake ◽  
Wake Field ◽  
Vortex Pairs ◽  
Probabilistic Function ◽  
Number Of Cycles

This paper describes an experimental study of the near wake of a circular cylinder subjected to streamwise flow forcing. The wake field is examined by PIV and LDV for excitation frequencies in which symmetric shedding is likely. The results show that symmetric formation of vortex pairs occurs close to the cylinder synchronized with the oscillatory component of the flow. The symmetric mode rapidly breaks down and gives rise to an antisymmetric arrangement of single vortices further downstream. The number of cycles for which the symmetrical vortices persist in the near wake is a probabilistic function of the excitation frequency and forcing amplitude. Details of the related wake kinematics and frequencies are shown and the findings are discussed in relation to symmetric vortex formation occurring in self-excited streamwise oscillations.

The Influence of Vortex Generators on the Drag and Heat Transfer From a Circular Cylinder Normal to an Airstream

1969 ◽  
Vol 91 (1) ◽  
pp. 91-99 ◽  
Author(s):  
T. R. Johnson ◽  
P. N. Joubert
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Angular Position ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Experimental Investigations ◽  
Stagnation Line

Experimental investigations were carried out to examine the effect of vortex generators on drag and heat transfer from a circular cylinder in a crossflow. The cylinder was fitted with two rows of vortex generators which were symmetrically placed on either side of and parallel to the front stagnation line. One configuration of vortex generator was used and the angular position of the rows from the front stagnation line was varied. In the heat transfer runs the vortex generator position remained unvaried. Results are presented to show the variation of drag coefficient with Reynolds number for several angular positions of the generator rows. Results are also presented to show the variation of Nusselt number with Reynolds number both for a cylinder with and without generators. These show that both decreases in drag coefficient and increases in Nusselt number can be obtained when vortex generators are fitted.

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.

scholarly journals Experiments on the flow past a circular cylinder at very high Reynolds number

1961 ◽  
Vol 10 (3) ◽  
pp. 345-356 ◽  
Author(s):  
Anatol Roshko
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Vortex Shedding ◽  
High Reynolds Number ◽  
Reynolds Numbers ◽  
A Value ◽  
High Reynolds ◽  
Very High

Measurements on a large circular cylinder in a pressurized wind tunnel at Reynolds numbers from 106 to 107 reveal a high Reynolds number transition in which the drag coefficient increases from its low supercritical value to a value 0.7 at R = 3.5 × 106 and then becomes constant. Also, for R > 3.5 × 106, definite vortex shedding occurs, with Strouhal number 0.27.

scholarly journals Control of vortex shedding around a circular cylinder using bubble tabs in the laminar flow regime

2021 ◽  
Vol 39 (4) ◽  
pp. 1108-1116
Author(s):  
E.O. Atofarati ◽  
A.O. Muritala ◽  
B.O. Malomo ◽  
S.A. Adio
Keyword(s):  
Circular Cylinder ◽  
Drag Coefficient ◽  
Vortex Shedding ◽  
Flow Analysis ◽  
Small Diameter ◽  
Ansys Fluent ◽  
Spacing Ratio ◽  
Flow Domain ◽  
Drag And Lift ◽  
Fatigue Failures

Vortex induced vibration (VIV) is the major cause of several catastrophic disasters due to fatigue failures induced by drag and lift forces in aerodynamic systems. This study investigates the control of VIV phenomenon through passive bubble tab(s) having a small diameter (d) relative to the main circular cylinder (D) in a two-dimensional (2-D) flow domain. Using ANSYS Fluent computational software, flow analysis was conducted at a Reynolds number (Re) of 80 for various bubble tab configurations at different spacing ratios (x/D) and diameter ratios (d/D). The drag coefficient, the velocity and pressure contours, along with the flow streamlines in eachcase were studied. The results indicated the optimized tab(s) positions for different spacing ratios, diameter ratios, and  configurations. The study effectively established that passive bubble tabs can potentially control VIV associated with flows around a circular cylinder. Keywords: Vortex Shedding; Drag Coefficient; Circular Cylinder; Bubble Tab(S); Spacing Ratio; Diameter Ratio.

Combined Influence of Fluid Viscoelasticity and Inertia on Forced Convection Heat Transfer From a Circular Cylinder

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
C. Sasmal ◽  
Mohd Bilal Khan ◽  
R. P. Chhabra
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Average Nusselt Number ◽  
A Priori ◽  
Convection Heat Transfer ◽  
Weissenberg Number ◽  
Elasticity Number

Abstract In this study, the combined influence of fluid viscoelasticity and inertia on the flow and heat transfer characteristics of a circular cylinder in the steady laminar flow regime have been studied numerically. The momentum and energy equations together with an appropriate viscoelastic constitutive equation have been solved numerically using the finite volume method over the following ranges of conditions: Reynolds number, 0.1≤Re≤20; elasticity number (= Wi/Re, where Wi is the Weissenberg number), 0≤El≤0.5; Prandtl number, 10≤Pr≤100 for Oldroyd-B and finitely extensible nonlinear elastic-Peterlin (FENE-P) (with two values of the chain extensibility parameter L2, namely 10 and 100) viscoelastic fluid models including the limiting case of Newtonian fluids (El = 0). New extensive results are presented and discussed in terms of the streamline and isotherm profiles, drag coefficient, distribution of the local and surface averaged Nusselt number. Within the range of conditions embraced here, the separation of boundary layers (momentum and thermal) is seen to be completely suppressed in an Oldroyd-B fluid whereas it is accelerated for a FENE-P fluid in comparison with that seen for a Newtonian fluid otherwise under identical conditions. At a fixed elasticity number, both the drag coefficient and average Nusselt number are seen to be independent of the Reynolds number beyond a critical value for an Oldroyd-B fluid. In contrast, the drag coefficient decreases and the average Nusselt number increases with Reynolds number for a FENE-P fluid at a constant value of the elasticity number. Finally, a simple correlation for the average Nusselt number for a FENE-P fluid is presented which facilitates the interpolation of the present results for the intermediate values of the governing parameters and/or its a priori estimation in a new application.

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