A PIV study of the near wake flow features of a square cylinder: influence of corner radius

2015 ◽  
Vol 29 (2) ◽  
pp. 527-541 ◽  
Author(s):  
R. Ajith Kumar ◽  
Chang Hyun Sohn ◽  
B. H. Lakshmana Gowda
Keyword(s):  
Wake Flow ◽  
Square Cylinder ◽  
Near Wake ◽  
Corner Radius ◽  
Flow Features

A laser-Doppler velocimetry study of ensemble-averaged characteristics of the turbulent near wake of a square cylinder

1995 ◽  
Vol 304 ◽  
pp. 285-319 ◽  
Author(s):  
D. A. Lyn ◽  
S. Einav ◽  
W. Rodi ◽  
J.-H. Park
Keyword(s):  
Circular Cylinder ◽  
Laser Doppler ◽  
Wake Flow ◽  
Shear Stresses ◽  
Square Cylinder ◽  
Base Region ◽  
Flow Topology ◽  
Near Wake ◽  
Flow Features ◽  
High Reynolds

Ensemble-averaged statistics at constant phase of the turbulent near-wake flow (Reynolds number ≈ 21400 around a square cylinder have been obtained from two-component laser-Doppler measurements. Phase was defined with reference to a signal taken from a pressure sensor located at the midpoint of a cylinder sidewall. The distinction is drawn between the near wake where the shed vortices are ‘mature’ and distinct and a base region where the vortices grow to maturity and are then shed. Differences in length and velocity scales and vortex celerities between the flow around a square cylinder and the more frequently studied flow around a circular cylinder are discussed. Scaling arguments based on the circulation discharged into the near wake are proposed to explain the differences. The relationship between flow topology and turbulence is also considered with vorticity saddles and streamline saddles being distinguished. While general agreement with previous studies of flow around a circular cylinder is found with regard to essential flow features in the near wake, some previously overlooked details are highlighted, e.g. the possibility of high Reynolds shear stresses in regions of peak vorticity, or asymmetries near the streamline saddle. The base region is examined in more detail than in previous studies, and vorticity saddles, zero-vorticity points, and streamline saddles are observed to differ in importance at different stages of the shedding process.

Effect of Dissimilar Leading Edges on the Flow Structures Around a Square Cylinder

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
R. Ajith Kumar ◽  
K. Arunkumar ◽  
C. M. Hariprasad
Keyword(s):  
Amplitude Ratio ◽  
Vortex Formation ◽  
Leading Edge ◽  
Wake Flow ◽  
Practical Significance ◽  
Flow Structures ◽  
Square Cylinder ◽  
Near Wake ◽  
Study Results ◽  
Leading Edges

In the present study, results of a flow visualization study on the flow around a square cylinder with dissimilar leading edges are presented. The radii of the leading edges of the cylinder “r1” and “r2” are such that the ratio r1/r2 is systematically varied from 0 to 1. The flow structures around the cylinder with different leading edge radii particularly the vortex shedding mode and mechanism are investigated. For studies with stationary as well as oscillated cylinder cases, the results are taken at a Reynolds number value of 2100. For the oscillated case, a special mechanism is made to oscillate the cylinders at a desired amplitude and frequency. That is, the cylinder undergoes forced oscillation in this case. Results indicate that dissimilar leading edges bring notable changes in the near-wake flow structures of a square cylinder. For the stationary cylinder cases, the vortex formation length decreases with increase in the r1/r2 ratio. Flow structures are also found to be influenced by the amplitude ratio (amplitude to body size ratio); the higher the amplitude, the larger the size of vortices shed per cycle of cylinder oscillation. In view of marine structures and building sections with similar geometries, the present results carry considerable practical significance.

Effect of Corner Cut on the Near Wake Flow Structures of a Square Cylinder

2014 ◽  
Author(s):  
Hariprasad Chakkalaparambil Many ◽  
Nagella Yashwanth ◽  
Haresh Bhardwaj ◽  
R. Ajith Kumar ◽  
B. H. Lakshmana Gowda
Keyword(s):  
Free Stream ◽  
Wake Flow ◽  
Practical Significance ◽  
Flow Structures ◽  
Stream Velocity ◽  
Square Cylinder ◽  
Sinusoidal Oscillation ◽  
Near Wake ◽  
Almost All ◽  
Sharp Corners

In this paper, results of a flow visualization study on the flow around a square section cylinder with corner chamfering are presented. The corners of the cylinder are chamfered so that the each corner forms a triangle with horizontal (stream-wise) and cross stream (perpendicular to the free stream velocity) dimension ‘b’. Experiments are conducted for b/B0 ratios of 0.05, 0.1, 0.2 and 0.3 where ‘B0’ is the side dimension of the uncut square cylinder. The flow structures, particularly the vortex shedding mode and mechanism around the cylinder with chamfered corners are investigated in order to deduce the effect of corner modifications on the flow. For studies with stationary cylinder (case (a)), the results are taken at Reynolds number values of 1500, 2100 and 2800. For sinusoidally oscillated cylinder case (case (b)), the studies are restricted to Re=2100. To bring out the effect of corner chamfering more clearly, experiments are also conducted with a square cylinder without corner cuts, i.e., with sharp corners. For the case (b), a special mechanism is made to oscillate the cylinders at a desired amplitude and frequency. That is, the cylinder undergoes forced sinusoidal oscillation in case (b). It is found that drag decreases and Strouhal number increases with b/B0 ratio. Quite uniquely, at b/B0=0.2, cross-stream convection of vortices have been observed. Vortex coalescence is observed in almost all cases. Results indicate that corner chamfering brings notable changes in the near-wake flow structures of a square section cylinder. In view of marine structures and building sections with similar geometries, the present results carry considerable practical significance.

Effect of Dissimilar Leading Edges on the Flow Structures Around a Square Cylinder

2014 ◽  
Author(s):  
Arunkumar Kumaran Nair ◽  
R. Ajith Kumar ◽  
Hariprasad Chakkalaparambil Many
Keyword(s):  
Amplitude Ratio ◽  
Vortex Formation ◽  
Leading Edge ◽  
Wake Flow ◽  
Practical Significance ◽  
Flow Structures ◽  
Square Cylinder ◽  
Near Wake ◽  
Study Results ◽  
Leading Edges

In the present study, results of a flow visualization study on the flow around a square cylinder with dissimilar leading edges are presented. The radii of the leading edges of the cylinder ‘r1’ and ‘r2’ are such that the ratio r1/ r2 is systematically varied from 0 to 1. The flow structures around the cylinder with different leading edge radii particularly the vortex shedding mode and mechanism are investigated. For studies with stationary as well as oscillated cylinder cases, the results are taken at a Reynolds number value of 2100. For the oscillated case, a special mechanism is made to oscillate the cylinders at a desired amplitude and frequency. That is, the cylinder undergoes forced oscillation in this case. Results indicate that dissimilar leading edges bring notable changes in the near-wake flow structures of a square cylinder. For the stationary cylinder cases, the vortex formation length decreases with increase in the r1/ r2 ratio. Flow structures are also found to be influenced by the amplitude ratio (amplitude to body size ratio); the higher the amplitude, the larger the size of vortices shed per cycle of cylinder oscillation. In view of marine structures and building sections with similar geometries, the present results carry considerable practical significance.

Near-Wake Flow Structures of a Corner-Chamfered Square Cylinder at Higher Harmonic Excitations

2015 ◽  
Author(s):  
M. S. Aswathy ◽  
K. K. Amrita ◽  
C. M. Hariprasad ◽  
R. Ajith Kumar
Keyword(s):  
Vortex Shedding ◽  
Water Channel ◽  
Wake Flow ◽  
Flow Structures ◽  
Square Cylinder ◽  
Near Wake ◽  
Harmonic Excitations ◽  
Vortex Shedding Frequency ◽  
Higher Harmonic ◽  
Vortex Shedding Modes

In this paper, the results of a flow visualization study on the flow structures around a chamfered square cylinder are presented. Square cylinders having side dimension Bo with corner chamfering ‘b’ are used such that b/Bo ratio assumes values 0, 0.1, 0.2 and 0.3. Corners of the square cylinder are equally cut by a measure ‘b’ both in the stream-wise and cross stream directions. Flow over these cylinders are visualized in a water channel. All the studies correspond to a Reynolds number value of 2100 (based on Bo). Results are taken for two situations (a) cylinders are stationary and (b) cylinders are oscillated at frequency ‘fe’. The main objective of this study is to investigate the near-wake flow structures around the cylinders at harmonic and higher harmonic excitations. Experiments were conducted for fe/fs= 1.0, 1.5, 2.0, 2.5 and 3.0 where fs is the vortex shedding frequency from the stationary cylinder for each b/Bo ratio. Peak-to-peak amplitude of excitation is kept at 1B in all cases. In this investigation, the main focus is on investigating the vortex shedding modes, mechanisms and the number of vortices shed per shear layer as the cylinder completes one oscillatory cycle as a function of fe/fs ratio.

scholarly journals Flow Turbulence Characteristics and Mass Transport in the Near-Wake Region of an Aquaculture Cage Net Panel

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 294
Author(s):  
Dongdong Shao ◽  
Li Huang ◽  
Ruo-Qian Wang ◽  
Carlo Gualtieri ◽  
Alan Cuthbertson
Keyword(s):  
Mass Transport ◽  
Near Field ◽  
Lateral Spreading ◽  
Wake Flow ◽  
Wake Region ◽  
Near Wake ◽  
Turbulence Characteristics ◽  
Macro Scale ◽  
Flow Turbulence ◽  
Fish Cages

Cage-based aquaculture has been growing rapidly in recent years. In some locations, cage-based aquaculture has resulted in the clustering of large quantities of cages in fish farms located in inland lakes or reservoirs and coastal embayments or fjords, significantly affecting flow and mass transport in the surrounding waters. Existing studies have focused primarily on the macro-scale flow blockage effects of fish cages, and the complex wake flow and associated near-field mass transport in the presence of the cages remain largely unclear. As a first step toward resolving this knowledge gap, this study employed the combined Particle Image Velocimetry and Planar Laser Induced Fluorescence (PIV-PLIF) flow imaging technique to measure turbulence characteristics and associated mass transport in the near wake of a steady current through an aquaculture cage net panel in parametric flume experiments. In the near-wake region, defined as ~3M (mesh size) downstream of the net, the flow turbulence was observed to be highly inhomogeneous and anisotropic in nature. Further downstream, the turbulent intensity followed a power-law decay after the turbulence production region, albeit with a decay exponent much smaller than reported values for analogous grid-generated turbulence. Overall, the presence of the net panel slightly enhanced the lateral spreading of the scalar plume, but the lateral distribution of the scalar concentration, concentration fluctuation and transverse turbulent scalar flux exhibited self-similarity from the near-wake region where the flow was still strongly inhomogeneous. The apparent turbulent diffusivity estimated from the gross plume parameters was found to be in reasonable agreement with the Taylor diffusivity calculated as the product of the transverse velocity fluctuation and integral length scale, even when the plume development was still transitioning from a turbulent-convective to turbulent-diffusive regime. The findings of this study provide references to the near-field scalar transport of fish cages, which has important implications in the assessment of the environmental impacts and environmental carrying capacity of cage-based aquaculture.

The Calculation of Train Slipstreams on Platform of Underground High-Speed Rail Station

2013 ◽  
Vol 842 ◽  
pp. 445-448
Author(s):  
Wei Chao Yang ◽  
Chuan He ◽  
Li Min Peng
Keyword(s):  
High Speed ◽  
Three Dimensional ◽  
Horizontal Distribution ◽  
Wake Flow ◽  
Railway Tunnel ◽  
Long Distance ◽  
Near Wake ◽  
High Speed Rail ◽  
Numerical Work ◽  
Rail Station

This paper describes the results of numerical work to determine the flow structures of the slipstream and wake of a high speed train on platforms of underground rail station using three-dimensional compressible Euler equation. The simulations were carried out on a model of a simplified three-coach train and typical cross-section of Chinese high-speed railway tunnel. A number of issues were observed: change process of slipstreams, longitudinal and horizontal distribution characteristics of train wind. Localized velocity peaks were obtained near the nose of the train and in the near wake region. Maximum and minimum velocity values were also noticed near to the nose rear tip. These structures extended for a long distance behind the train in the far wake flow. The slipstream in platform shows the typical three-dimensional characteristics and the velocity is about 4 m/s at 6 m away from the edge of platform.

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