Experimental Study on the Near Wake Behind Two Staggered Cylinders of Unequal Diameters

2012 ◽  
Author(s):  
Yangyang Gao ◽  
Xikun Wang ◽  
Soon Keat Tan
Keyword(s):  
Reynolds Stress ◽  
Incident Angle ◽  
Reynolds Shear Stress ◽  
Flow Characteristics ◽  
Circular Cylinders ◽  
Mean Flow ◽  
Near Wake ◽  
Particle Image Velocimetry Technique ◽  
Image Velocimetry ◽  
Spacing Ratio

The wake structure behind two staggered circular cylinders with unequal diameters was investigated experimentally using the particle image velocimetry technique (PIV). This investigation was focused on the variations of flow patterns in terms of incident angle at Reynolds number Re = 1200. Comparisons of the time-averaged flow field of two staggered cylinders with unequal diameters at different angles were made to elucidate the mean flow characteristics. The characteristics of Reynolds shear stress contours at different incident angles and spacing ratios were also investigated. The results showed that with increasing of incident angle, the scale of Reynolds stress contours behind the upstream cylinder becomes larger, as well as the effect of spacing ratio on Reynolds stress contours.

PIV Investigation of Turbulent Flow Over a Wavy-Wall in a Horizontal Channel

2016 ◽  
Author(s):  
Vinicius Martins Segunda ◽  
Mark Tachie ◽  
Scott Ormiston
Keyword(s):  
Turbulent Flow ◽  
Reynolds Shear Stress ◽  
Flow Characteristics ◽  
Wavy Wall ◽  
Mean Flow ◽  
Particle Image Velocimetry Technique ◽  
Turbulent Characteristics ◽  
Developing Region ◽  
Contour Plots ◽  
The Mean

Experimental investigation of turbulent flow in a channel with flat upper wall and wavy lower wall using a particle image velocimetry technique is presented. The mean flow and turbulent characteristics in both the developing region and fully periodic region over the wavy wall were examined. It was observed that the flow characteristics become fully periodic after the eighth wave. The results also showed that the separation and reattachment points within the developing region and fully periodic region are similar. Detailed investigation of the flow field in the fully periodic region was examined using contour plots and one-dimensional profiles of the mean velocities, mean spanwise vorticity, streamwise and wall-normal turbulence intensities and Reynolds shear stress.

Experimental Study of Turbulent Cross-Flow Over Two Circular Cylinders Adjacent to Wall and Free Surface Boundaries

2007 ◽  
Author(s):  
S. S. Paul ◽  
M. F. Tachie ◽  
S. J. Ormiston
Keyword(s):  
Free Surface ◽  
Reynolds Shear Stress ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Particle Image Velocimetry Technique ◽  
Mean Velocity ◽  
Image Velocimetry ◽  
Vertical Location ◽  
Approach Velocity ◽  
Velocity Turbulence

A particle image velocimetry technique was used to study fluid flow around two identical circular cylinders arranged side-by-side with a fixed center-to-center distance. The vertical location of the cylinder pair was varied. The cylinders spanned the tunnel test-section and were oriented normal to the streamwise direction. The Reynolds number based on the cylinder diameter and the approach velocity was 2030. The mean velocity, turbulence intensities, Reynolds shear stress, and momentum flux distributions are used to study the influence on the flow of the free surface at the top of the tunnel and the wall at the bottom of the tunnel.

Numerical Simulation for Flow over Two Circular Cylinders in Micro Channel with Lattice Boltzmann Method

2014 ◽  
Vol 670-671 ◽  
pp. 747-750
Author(s):  
Zhi Jun Gong ◽  
Jiao Yang ◽  
Wen Fei Wu
Keyword(s):  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Recirculation Zone ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Micro Channel ◽  
Zone Length ◽  
Spacing Ratio ◽  
Boltzmann Method

For indepth study on flow characteristics for fluid bypass obstacles in micro-channel, the Lattice Boltzmann Method (LBM) was used to simulate fluid flow over two circular cylinders in side-by-side arrangement of a micro-channel. The velocity distribution and recirculation zone length under different Reynolds numbers (Re = 0~100) and different spacing ratio (H/D= 0~2.0) were obtained. The results show that the pattern of flow and the size of recirculation zone in the micro-channel depend on the combined effect of Re and H/D.

Near-field mean flow dynamics of a cylindrical canopy patch suspended in deep water

2018 ◽  
Vol 858 ◽  
pp. 634-655 ◽  
Author(s):  
Jian Zhou ◽  
Subhas K. Venayagamoorthy
Keyword(s):  
Deep Water ◽  
Near Field ◽  
Flow Dynamics ◽  
Flow Diversion ◽  
Circular Cylinders ◽  
Published Data ◽  
Global Flow ◽  
Mean Flow ◽  
Near Wake ◽  
Local Flow

The time-averaged flow dynamics of a suspended cylindrical canopy patch with a bulk diameter of $D$ is investigated using large-eddy simulations (LES). The patch consists of $N_{c}$ constituent solid circular cylinders of height $h$ and diameter $d$, mimicking patchy vegetation suspended in deep water ($H/h\gg 1$, where $H$ is the total flow depth). After validation against published data, LES of a uniform incident flow impinging on the canopy patch was conducted to study the effects of canopy density ($0.16\leqslant \unicode[STIX]{x1D719}=N_{c}(d/D)^{2}\leqslant 1$, by varying $N_{c}$) and bulk aspect ratio ($0.25\leqslant AR=h/D\leqslant 1$, by varying $h$) on the near-wake structure and adjustment of flow pathways. The relationships between patch geometry, local flow bleeding (three-dimensional redistribution of flow entering the patch) and global flow diversion (streamwise redistribution of upstream undisturbed flow) are identified. An increase in either $\unicode[STIX]{x1D719}$ or $AR$ decreases/increases/increases bleeding velocities through the patch surface area along the streamwise/lateral/vertical directions, respectively. However, a volumetric flux budget shows that a larger $AR$ causes a smaller proportion of the flow rate entering the patch to bleed out vertically. The global flow diversion is found to be determined by both the patch geometrical dimensions and the local bleeding which modifies the sizes of the patch-scale near wake. While loss of flow penetrating the patch increases monotonically with increasing $\unicode[STIX]{x1D719}$, its partition into flow diversion around and beneath the patch shows a non-monotonic dependence. The spatial extents of the wake, the flow-diversion dynamics and the bulk drag coefficients of the patch jointly reveal the fundamental differences of flow responses between suspended porous patches and their solid counterparts.

scholarly journals The Effect of Boattail Angles on the Near-Wake Structure of Axisymmetric Afterbody Models at Low-Speed Condition

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
The Hung Tran
Keyword(s):  
Strouhal Number ◽  
Reynolds Shear Stress ◽  
Flow Behavior ◽  
Flow Characteristics ◽  
Wake Flow ◽  
Turbulent Intensity ◽  
Near Wake ◽  
Wake Structure ◽  
Low Speed ◽  
Speed Condition

The effect of a boattail angle on the structure of the wake of an axisymmetric model was investigated at low-speed condition. Four conical boattail models with angles of 0° (blunt-based body), 10°, 16°, and 22° were selected for this study. The Reynolds number based on the diameter of the model was around 1.97×104. Particle image velocimetry (PIV) was used to measure the velocity of the wake flow. The time-averaged flow characteristics including the length of recirculation of the afterbody, turbulent intensity, and Reynolds shear stress were analyzed and compared among those boattail models. The experimental results showed that the length of recirculation decreases with increasing boattail angle to 16°. At a boattail angle above 16°, the flow was fully separated near the shoulder and near-wake structure was highly changed. The turbulent intensity at a boattail angle of 22° showed a similar level to that in the case of the blunt-based body. Flow behavior on boattail surface should be accounted as an important parameter affecting the wake width and drag of the model. Power spectral density and proper orthogonal decomposition (POD) analyses showed that a Strouhal number of StD=0.2 dominated for the boattail model up to 16°. The fully separated flow was dominated by a Strouhal number of StD=0.03−0.06, which was firstly presented in this study.

Particle Image Velocimetry Measurements of the Mean Flow Characteristics in a Bubble Plume

2007 ◽  
Vol 133 (6) ◽  
pp. 665-676 ◽  
Author(s):  
Dong-Guan Seol ◽  
Tirtharaj Bhaumik ◽  
Christian Bergmann ◽  
Scott A. Socolofsky
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Flow Characteristics ◽  
Bubble Plume ◽  
Mean Flow ◽  
Image Velocimetry ◽  
The Mean

An Experimental Investigation of Turbulent Drag Reduction in Concentric Annulus Using Particle Image Velocimetry Technique

2013 ◽  
Author(s):  
Fabio Ernesto Rodriguez Corredor ◽  
Majid Bizhani ◽  
Ergun Kuru
Keyword(s):  
Particle Image Velocimetry ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Particle Image ◽  
Reynolds Shear Stress ◽  
Polymer Concentration ◽  
Mean Flow ◽  
Flow Loop ◽  
Mean Velocity ◽  
Image Velocimetry

Polymer drag reduction is investigated using the Particle Image Velocimetry (PIV) technique in fully developed turbulent flow through a horizontal flow loop with concentric annular geometry (inner to outer pipe radius ratio = 0.4). The polymer used was a commercially available partially hydrolyzed polyacrylamide (PHPA). The polymer concentration was varied from 0.07 to 0.12% V/V. The drag reduction is enhanced by increasing polymer concentration until the concentration reaches an optimum value. After that, the drag reduction is decreased with the increasing polymer concentration. Optimum concentration value of PHPA was found to be around 0.1% V/V. Experiments were conducted at solvent Reynolds numbers of 38700, 46700 and 56400. The percent drag reduction was found to be increasing with the increasing Reynolds number. The study was also focused on analyzing the mean flow and turbulence statistics for fully-turbulent flow using the velocity measurements acquired by PIV. Axial mean velocity profile was found to be following the universal wall law close to the wall (i.e., y+ <10), but it deviated from log law results with an increased slope in the logarithmic zone (i.e., y+ >30). In all cases of polymer application, the viscous sublayer (i.e., y+ <10) thickness was found to be higher than that of the water flow. Reynolds shear stress in the core flow region was found to be decreasing with the increase in polymer concentration.

Influence of Wall Proximity and Free Surface on Wake of Two Side-by-Side Circular Cylinders: PIV Measurement and POD Analysis

2010 ◽  
Author(s):  
S. S. Paul
Keyword(s):  
Free Surface ◽  
Large Scale ◽  
Circular Cylinders ◽  
Particle Image Velocimetry Technique ◽  
Large Scale Structures ◽  
Turbulent Statistics ◽  
Piv Measurement ◽  
Image Velocimetry ◽  
Pitch Ratio ◽  
Pod Analysis

The paper reports on an experimental study of turbulent flow around a pair of circular cylinders with a pitch ratio of two. The cylinders were located in the vicinity of a plane wall, in a uniform stream, and adjacent to a free surface in an open channel. The Reynolds number based on depth of flow and fresstream velocity was 30300 while the Froude number was 0.3. A particle image velocimetry technique was used to conduct detailed velocity measurements around and in the near wake region of the cylinder pairs, from which contours and profiles of the mean velocities and turbulent statistics were obtained and discussed. The proper orthogonal decomposition was then applied to provide an insight into the structure of the flow. Reconstruction of the fluctuating velocity components for various numbers of modes were also shown to investigate the role of large-scale structures.

Turbulent Flow Over Cavities in an Asymmetric Diverging Channel

2007 ◽  
Author(s):  
M. K. Shah ◽  
M. F. Tachie
Keyword(s):  
Turbulent Flow ◽  
Reynolds Shear Stress ◽  
Adverse Pressure Gradient ◽  
Particle Image Velocimetry Technique ◽  
Mean Velocity ◽  
Freestream Velocity ◽  
Aspect Ratios ◽  
Image Velocimetry ◽  
Diverging Channel ◽  
Single Cavity

An experimental investigation of turbulent flow over a single cavity in an asymmetric diverging channel is presented. Cavities of two different aspect ratios, w/h = 1 and 4, of height h = 6 mm were studied. The Reynolds number based on the approach freestream velocity and cavity height was Reh = 5000. Particle image velocimetry technique (PIV) was used to conduct detailed velocity measurements upstream of the cavity, inside the cavity and as far downstream of the cavity as x/h = 50. Mean velocity, turbulent intensities and Reynolds shear stress were obtained to document the effect of the cavity on the flow in the presence of adverse pressure gradient.

Wake Formation for an Oscillating Small-Incidence-Angle Cylinder Pair in Cross-Flow

2011 ◽  
Author(s):  
Mir M. Hayder
Keyword(s):  
Incidence Angle ◽  
Flow Direction ◽  
Incident Angle ◽  
Cross Flow ◽  
Wake Flow ◽  
Circular Cylinders ◽  
Mean Flow ◽  
Small Incidence ◽  
The Mean ◽  
Wake Formation

The wake region of a pair of equal-diameter staggered circular cylinders in cross-flow is investigated experimentally for Reynolds numbers, based on the mean flow velocity, U, and the cylinder diameter, D, within the range 540 ≤ Re ≤ 755. The centre-to-centre pitch ratio and stagger angle of the cylinders at their mean position are P/D = 2.0 and α = 16°, respectively. In an earlier study, wake formation of a small-incident-angle cylinder pair was investigated for forced oscillation (transverse to the flow direction) of the upstream cylinder only. The present study is aimed to reveal the modification of the wake when the oscillation is shifted from the upstream to downstream cylinder or vice versa. Results with cylinder excitation frequencies in the range 0.07 ≤ feD/U ≤ 1.10 are reported. It is observed that for both upstream and downstream cylinder oscillations with frequency feD/U ≤ 0.10 the wake flow patterns remain essentially the same as those of the corresponding static cases. However, for frequency feD/U &gt; 0.10 the wake undergoes considerable modification vis-a`-vis when the cylinders are stationary, and the flow pattern within the wake is strongly dependent on feD/U value. As also observed in the previous study, there are distinct regions of synchronization between the dominant wake periodicities and the cylinder oscillation over the whole range of feD/U. These synchronizations involve sub- and super-harmonics as well as fundamental synchronizations and are the result of the formation of two rows of vortices, one on either side of the combined wake of the cylinder pair. The manner in which the wake responds to the cylinder oscillation depends strongly on whether it is the upstream or downstream cylinder which is oscillating. Flow-visualization images suggests that the synchronizations on the mean-flow side of the downstream cylinder occur from the outer vortices shed by the downstream cylinder, and those on the mean-flow side of the upstream cylinder occur from the vortices formed by the interaction of the two gap shear layers and the outer shear layer separated from the upstream cylinder.

Sign in / Sign up

Export Citation Format

Share Document