Square-Cylinder Flow Characteristics Modulated Using Upstream Control Rod

2012 ◽  
Vol 28 (2) ◽  
pp. 279-289 ◽  
Author(s):  
S. C. Yen ◽  
S. F. Wu
Keyword(s):  
Surface Pressure ◽  
Vortex Shedding ◽  
Flow Characteristics ◽  
Flow Patterns ◽  
Square Cylinder ◽  
Control Rod ◽  
Pressure Profiles ◽  
Spacing Ratio ◽  
Cylinder Flow ◽  
Upstream Control

AbstractThe flow patterns, vortex-shedding frequency and aerodynamic performance of the square-cylinder flow were modulated using an upstream control rod. Additionally, the flow behaviors were examined using various Reynolds numbers, rotation angles, and spacing ratios. The flow patterns were visualized using the smoke-wire scheme. The global velocity fields and streamline patterns were analyzed using the particle image velocimetry (PIV). Additionally, the flow modes were characterized based on the kinematics theory. Moreover, the vortex-shedding frequencies behind upstream control rod and the square cylinder were detected using two hot-wire anemometers. The surface pressure on square cylinder was determined using a linear pressure scanner. Then, the aerodynamic parameters were calculated using the surface-pressure profiles. Three characteristic flow modes — single, attached, and bi-vortex-street — were categorized by varying the Reynolds number and spacing ratio. In the attached mode, the position of upstream control rod determined the flow characteristics. Furthermore, in the attached mode, the mean drag force of the square cylinder is about 57% lower than of single-square cylinder.

scholarly journals Visualization of flow past square cylinders with corner modification

2020 ◽  
Vol 4 (3) ◽  
pp. 285-294
Author(s):  
Ch. Krishnappa Vikram ◽  
H. V. Ravindra ◽  
Y. T. Krishnegowda
Keyword(s):  
Aluminum Powder ◽  
Experimental Work ◽  
Vortex Shedding ◽  
Test Section ◽  
Square Cylinder ◽  
Square Cylinders ◽  
Flow Past ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

This article presents the results for flow past a square cylinder and two square cylinders of the same and different sizes with corner modifications by varying the spacing ratio. Here, experimental work is conducted in a recirculatory channel filled with water. A set of aluminum discs made to rotate to create the flow in the test section. The motor is used to vary the speed of the water. Fine aluminum powder is used as a tracer medium. It is observed that vortex shedding frequency decreases by placing the second cylinder in the downstream of the first cylinder. For similar size cylinders, the width of the eddy in the middle of the cylinders increases with an increase in spacing ratio. With the increase of spacing ratio to 6, the flow past each cylinder behaves like a single square cylinder. If the upstream square cylinder size is smaller than the downstream square cylinder, the eddy size is reduced in between the cylinder compared to the downstream of the second cylinder. If the upstream square cylinder size is bigger than the downstream square cylinder, the eddy size is larger in between the cylinder compared to the downstream of the second cylinder.

Interaction of Oscillatory Flows with a Square Cylinder

2007 ◽  
Vol 23 (4) ◽  
pp. 445-450 ◽  
Author(s):  
M.-J. Chern ◽  
Y.-J. Lu ◽  
S.-C. Chang ◽  
I.-C. Cheng
Keyword(s):  
Vortex Shedding ◽  
Flow System ◽  
Flow Patterns ◽  
Oscillating Flow ◽  
Square Cylinder ◽  
Asymmetric Vortex ◽  
Force Coefficients ◽  
Periodic State ◽  
Highly Nonlinear ◽  
Line Force

AbstractThe behaviour of vortices induced by a single square cylinder in an oscillating flow was investigated. The flow patterns in the vicinity of square cylinders were visualized using an in-house numerical model. Meanwhile, force coefficients exerted on the square cylinder were determined numerically. In terms of various Keulegan-Carpenter (KC) numbers, it turns out that the flow patterns for an oscillating flow past a single cylinder can be divided into three modes: (i) no vortex, (ii) pairs of symmetric vortices, and (iii) asymmetric vortex shedding. Reynolds (Re) number did not affect the flow field apparently in this study. In addition, the in-line force coefficient decreases exponentially as KC increases. Spectrum analysis of in-line force coefficients for various KCs was provided. It can be found that the flow system was at a periodic state at small KC for the first two modes. Variations of the flow system from a periodic state to a highly nonlinear state in which asymmetric vortex shedding appeared were demonstrated for increasing KC. The relationship between the in-line force and KC was provided for future applications.

scholarly journals Flow Characteristics in the Volute and Tongue Region of a Centrifugal Pump

1984 ◽  
Author(s):  
R. B. Brownell ◽  
R. D. Flack
Keyword(s):  
Rotational Speed ◽  
Separation Zone ◽  
Flow Characteristics ◽  
Flow Patterns ◽  
High Flow ◽  
Low Flow ◽  
Flow Rates ◽  
Pressure Profiles ◽  
Instantaneous Position ◽  
Centrifugal Process

A centrifugal process pump was tested at two rotational speeds and five flow rates. Nine piezometer taps around the volute were used to measure time averaged pressure profiles and streak photography was used to visualize the flow patterns near the volute tongue. Flow patterns for four different instantaneous impeller orientations (blade positions) were studied. Nondimensionalized results were independent of rotational speed. At 100% capacity the volute pressures were uniform within 15%. At off-design condition, however, the pressure near the tongue varied by as much as 28% from the average. At 100% capacity the streamlines were smooth and well behaved. At low flow rates the tongue stagnation point moved between the impeller and tongue and a separation zone appeared in the discharge. The instantaneous position of the impeller was seen to affect the streamlines primarily near the impeller, although at high flow rates the separation zone was also seen to depend on the impeller position.

scholarly journals Numerical Computations for Flow Patterns and Force Statistics of Three Rectangular Cylinders

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Hamid Rahman ◽  
Shams-ul-Islam ◽  
Waqas Sarwar Abbasi ◽  
Raheela Manzoor ◽  
Fazle Amin ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Vortex Shedding ◽  
Lift Coefficient ◽  
Flow Characteristics ◽  
Drag And Lift Coefficients ◽  
Aspect Ratios ◽  
Spacing Ratio ◽  
Drag And Lift ◽  
Rectangular Cylinders

In this work, numerical simulations are performed in order to study the effects of aspect ratio (AR) and Reynolds number (Re) on flow characteristics of three side-by-side rectangular cylinders for fixed spacing ratio ( g ), using the lattice Boltzmann method (LBM). The Reynolds number varies within the range 60 ≤ Re ≤ 180, aspect ratio is between 0.25 and 4, and spacing ratio is fixed at g  = 1.5. The flow structure mechanism behind the cylinders is analyzed in terms of vorticity contour visualization, time-trace analysis of drag and lift coefficients, power spectrum analysis of lift coefficient and variations of mean drag coefficient, and Strouhal number. For different combinations of AR and Re, the flow is characterized into regular, irregular, and symmetric vortex shedding. In regular and symmetric vortex shedding the drag and lift coefficients vary smoothly while reverse trend occurs in irregular vortex shedding. At small AR, each cylinder experiences higher magnitude drag force as compared to intermediate and large aspect ratios. The vortex shedding frequency was found to be smaller at smaller AR and increased with increment in AR.

Mach number effects on vortex shedding of a square cylinder and thick symmetrical airfoil arranged in tandem

1986 ◽  
Vol 407 (1833) ◽  
pp. 283-297 ◽  
Keyword(s):  
Mach Number ◽  
Shock Waves ◽  
Vortex Shedding ◽  
Pressure Fluctuations ◽  
Shear Layers ◽  
Side Length ◽  
Square Cylinder ◽  
Formation Region ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency

An experimental study was done to elucidate the Mach number effects on vortex shedding of a square cylinder (side length D = 20 mm) and thick symmetrical airfoil (NACA 0018, chord length 20 mm) arranged in tandem , at free stream Mach numbers between 0.1526 and 0.9081, and at free stream Reynolds numbers (based on the side length D ) between 0.702 x 10 5 and 4.188 x 10 5 . The spacing ratio of the central distance, L , between the square cylinder and the airfoil to the side length, D , of the square cylinder was varied from 1.125 to 5.5. It was found that the regular vortex shedding is not suppressed by steady shock waves in the local supersonic flow regions; the periodic vortex shedding is still present, irrespective of the appearance of the shock waves. When the spacing ratio is fixed, the Strouhal number behind the square cylinder is almost constant up to the critical Mach number of about 0.70, but it increases rapidly with further increase of the Mach number. However, once the shock waves are formed on both sides of the vortex formation region, various frequency components, other than the vortex shedding frequency appear; the spectral peaks lower than those of the vortex shedding frequency were identified as frequencies of an acoustic-feedback oscillation and the resonance of the wind tunnel structural system. With increasing the Mach number, the formation region becomes small and asymmetric, and the separating shear layers become wavy. These changes result in an increase of the scale and strength of the vortices and thus enhance the vortex shedding process. However, when the Mach number exceeds the critical value, the streamwise length of the formation region increases suddenly and becomes long enough to enclose the downstream airfoil. Under this circumstance, the formation region is almost symmetrical with respect to the wake axis, and shock waves are formed on the upper and lower separating shear layers. The shock waves are almost normal to the wake axis at M = 0.7512 and 0.8215, but incline to the downstream direction at M = 0.9081. Acoustic waves travelling upstream have been observed most clearly when the vortex shed from the square cylinder hits the leading edge of the airfoil at a Mach number of about 0.63, which is close to, but slightly smaller than the critical value. The mean pressure and the amplitude of the pressure fluctuations in the test section decreases and increases, respectively, with increasing the Mach number. However, the amplitude of the pressure fluctuations decreases suddenly when the steady shock waves are formed on the upper and lower separating shear layers.

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.

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.

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