scholarly journals Numerical Study on Flow around Four Square-Arranged Cylinders at Low Reynolds Numbers

2017 ◽  
Vol 2017 ◽  
pp. 1-18 ◽  
Author(s):  
Yang-yang Gao ◽  
Chang-shan Yin ◽  
Hao-qiang Zhang ◽  
Kang Yang ◽  
Xi-zeng Zhao ◽  
...  
Keyword(s):  
Vortex Shedding ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Low Reynolds Numbers ◽  
Force Coefficients ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency ◽  
Four Square

In this paper, numerical simulations of flow past four square-arranged cylinders are carried out at different spacing ratios (1.5≤L/D≤5.0; L is the center to center distance; D is the cylinder diameter) and Reynolds numbers (100≤Re≤1000). The effects of spacing ratio and Reynolds number on the wake flow characteristics are investigated, such as the instantaneous vorticity contours, force coefficients, and vortex shedding frequencies. The results show that the flow characteristics behind the four-cylinder cases are significantly affected by the spacing ratios and Reynolds numbers. At the same spacing ratio, the transformation of flow pattern is advanced quickly with increasing of Reynolds numbers, the values of force coefficients are correspondingly fluctuated with large amplitude, and the vortex shedding frequency is increased significantly with Re.

An Experimental Study on the Vertical Flow Past a Finite-Length Horizontal Cylinder at Low Reynolds Numbers

2014 ◽  
Vol 493 ◽  
pp. 68-73 ◽  
Author(s):  
Willy Stevanus ◽  
Yi Jiun Peter Lin
Keyword(s):  
Finite Length ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Horizontal Cylinder ◽  
Vortex Street ◽  
Vertical Flow ◽  
Low Reynolds Numbers ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The research studies the characteristics of the vertical flow past a finite-length horizontal cylinder at low Reynolds numbers (ReD) from 250 to 1080. The experiments were performed in a vertical closed-loop water tunnel. Flow fields were observed by the particle tracer approach for flow visualization and measured by the Particle Image Velocimetry (P.I.V.) approach for velocity fields. The characteristics of vortex formation in the wake of the finite-length cylinder change at different regions from the tip to the base of it. Near the tip, a pair of vortices in the wake was observed and the size of the vortex increased as the observed section was away from the tip. Around a distance of 3 diameters of the cylinder from its tip, the vortex street in the wake was observed. The characteristics of vortex formation also change with increasing Reynolds numbers. At X/D = -3, a pair of vortices was observed in the wake for ReD = 250, but as the ReD increases the vortex street was observed at the same section. The vortex shedding frequency is analyzed by Fast Fourier Transform (FFT). Experimental results show that the downwash flow affects the vortex shedding frequency even to 5 diameters of the cylinder from its tip. The interaction between the downwash flow and the Von Kármán vortex street in the wake of the cylinder is presented in this paper.

Unsteady numerical investigation of two different corrugated airfoils

2016 ◽  
Vol 231 (13) ◽  
pp. 2423-2437 ◽  
Author(s):  
WH Ho ◽  
TH New
Keyword(s):  
Large Scale ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Mean Flow ◽  
Airfoil Surface ◽  
Low Reynolds Numbers ◽  
Corrugated Surfaces ◽  
Large Scale Flow ◽  
Lift And Drag

An unsteady, two-dimensional numerical study was conducted to investigate the aerodynamic and flow characteristics of two bio-inspired corrugated airfoils at Re = 14,000 and compared with those of a smooth NACA0010 airfoil. Mean aerodynamic results reveal that the corrugated airfoils have better lift performance compared to the NACA0010 airfoil but incur slightly higher drag penalty. Mean flow streamlines indicate that this favourable performance is due to the ability of the corrugated airfoils in mitigating large-scale flow separations and stall. Unsteady flow field results show persistent formations of small recirculating vortices that remain within the corrugations at 10° angle-of-attack or less for one of the corrugated airfoil and below 15° for the other. In contrast, the flow behaviour can be highly turbulent with regular pairings of large-scale flow separation vortices along the upper surface at higher angles-of-attack. This not only disrupts the small recirculating vortices and causes them to detach from the corrugated surfaces, but it gets increasingly dominant at higher angles-of-attack resulting in regular lift and drag oscillations. At the end of each cycle, there is a sudden ejection of flow perpendicular to the airfoil surface and these disruptions manifest themselves as “kinks” in the instantaneous lift and drag of the corrugated airfoils. Therefore instead of regular fluctuations, the lift and drag curves have additional undulations. Despite that, the corrugations are able to produce larger pressure differentials between the upper and lower surfaces than the smooth airfoil. The current study demonstrates the intricate relationships between different sharp surface corrugations and favourable aerodynamic performance. In particular, results from this paper supports earlier investigations that corrugated airfoils may be used to good effects even at low Reynolds numbers, where flow separations are more likely.

scholarly journals Numerical study on the flow characteristics of micro air vehicle wings at low Reynolds numbers

2016 ◽  
Vol 8 (1) ◽  
pp. 29-40 ◽  
Author(s):  
Tianhang Xiao ◽  
Zhengzhou Li ◽  
Shuanghou Deng ◽  
Haisong Ang ◽  
Xinchun Zhou
Keyword(s):  
Numerical Study ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Micro Air Vehicle ◽  
Low Reynolds Numbers ◽  
Air Vehicle ◽  
Low Reynolds

Experiments on Vortex Shedding From Reconfigured Flexible Filaments Vibrating in Flow

2019 ◽  
Author(s):  
Jorge Silva-Leon ◽  
Andrea Cioncolini
Keyword(s):  
Aspect Ratio ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Aspect Ratios ◽  
Inclination Angles ◽  
Spanwise Vortex ◽  
Vortex Shedding Frequency

Abstract This paper describes an experimental study of the spanwise vortex shedding frequencies from cantilever flexible filaments which are bent (reconfigured) when exposed to air crossflow. At a reduced velocity of approximately U* = 1500 (based on filament diameter) the filaments started to vibrate in the inline direction. Hot-wire anemometry was thus employed to investigate the wake flow of filaments of three aspect ratios (L/D = 38, 80, and 113) at Reynolds numbers Re < 300. Despite the large relative inclination angles between the filament and the flow direction, the vortex shedding frequency measured along the span of the filaments remained close to those of a cylinder in pure crossflow. Moreover, it was found that as the aspect ratio (axial length) of the filaments was increased, vortex shedding lost coherence towards the free end of the filaments, whereas this was not the case for the shortest aspect ratio filament currently tested. This is thought to be due to the interaction between the crossflow vortex shedding and the axial flow component developing along the wake of the inclined filaments. Through comparisons with stiff inclined wires it was confirmed that the spanwise vortex shedding behaviors observed (frequency and coherence) were not modulated by the motions of the filaments.

Vortex shedding from spheres

1974 ◽  
Vol 62 (2) ◽  
pp. 209-221 ◽  
Author(s):  
Elmar Achenbach
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Critical Reynolds Number ◽  
Measurement Techniques ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Present Measurement ◽  
Number Range ◽  
Low Reynolds Numbers ◽  
The Relationship

Vortex shedding from spheres has been studied in the Reynolds number range 400 < Re < 5 × 106. At low Reynolds numbers, i.e. up to Re = 3 × 103, the values of the Strouhal number as a function of Reynolds number measured by Möller (1938) have been confirmed using water flow. The lower critical Reynolds number, first reported by Cometta (1957), was found to be Re = 6 × 103. Here a discontinuity in the relationship between the Strouhal and Reynolds numbers is obvious. From Re = 6 × 103 to Re = 3 × 105 strong periodic fluctuations in the wake flow were observed. Beyond the upper critical Reynolds number (Re = 3.7 × 105) periodic vortex shedding could not be detected by the present measurement techniques.The hot-wire measurements indicate that the signals recorded simultaneously at different positions on the 75° circle (normal to the flow) show a phase shift. Thus it appears that the vortex separation point rotates around the sphere. An attempt is made to interpret this experimental evidence.

Phenomena of vortex shedding and flow interference of three cylinders in different equilateral arrangements

1988 ◽  
Vol 196 ◽  
pp. 1-26 ◽  
Author(s):  
K. Lam ◽  
W. C. Cheung
Keyword(s):  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Injection Technique ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Visualization Experiments ◽  
Flow Interference ◽  
Bistable Flow

This paper describes how the flows around three equal circular cylinders arranged in an equilateral-triangular manner interact at different angles of incidence α and spacing ratios l/d. Some vortex-shedding-frequency data evaluated from flow visualization experiments conducted at Reynolds numbers of 2.1 × 103 and 3.5 × 103, based on the diameter of a single cylinder, using a dye -injection technique, are presented. In order to provide additional insight to the understanding of the flow structure around this particular cylinder array, some photographs indicating the typical flow patterns for various arrangements are also presented. The investigation indicates that the flows interact in a complex fashion for spacing ratios smaller than 2.29 and it also reveals that, at this range of spacing ratios and at α = 0°, bistable flow characteristic exists. Moreover, for l/d approximately smaller than 4.65 there always exists an angle at which the vortex shedding behind an upstream cylinder is suppressed by a nearest downstream cylinder. This angle is found not to remain constant but increases as the spacing ratio increases. For illustration and comparisons, some numerical results obtained from the application of the surface-vorticity method have also been presented.

Suppression of Vortex Shedding of Circular Cylinder by a Small Control Rod

2013 ◽  
Vol 477-478 ◽  
pp. 265-270 ◽  
Author(s):  
Li-Chieh Hsu ◽  
De-Chang Lai ◽  
Jian-Zhi Ye
Keyword(s):  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Near Wake ◽  
Control Rod ◽  
Low Reynolds Numbers ◽  
Numerical Studies ◽  
Vortex Shedding Frequency ◽  
Physical Phenomena ◽  
Control Cylinder

The physical phenomena of vortex suppression and flow patterns by deploying a very mall control cylinder in the near wake region of a main cylinder in low Reynolds numbers is studied numerically. The control diameter effect on vortex suppression and three flow patterns has been studied. The results shows the control cylinder can reduce vortex shedding frequency and suppress shedding partially or completely dependent on the diameter of control cylinder and Reynolds number. The results of a cylinder with control and without control agree with experimental and numerical studies.

Sign in / Sign up

Export Citation Format

Share Document