Comparison of flow patterns in the near wake of a circular cylinder and a square cylinder placed near a plane wall

2008 ◽  
Vol 35 (5-6) ◽  
pp. 458-472 ◽  
Author(s):  
X.K. Wang ◽  
S.K. Tan
Keyword(s):  
Circular Cylinder ◽  
Flow Patterns ◽  
Plane Wall ◽  
Square Cylinder ◽  
Near Wake

Interference Between a Square and a Circular Cylinder

2015 ◽  
Author(s):  
Nithin S. Kumar ◽  
R. Ajith Kumar ◽  
Jayalakshmi Mohan
Keyword(s):  
Circular Cylinder ◽  
Flow Visualization ◽  
Shear Layer ◽  
Flow Pattern ◽  
Water Channel ◽  
Flow Patterns ◽  
Observation Time ◽  
Square Cylinder ◽  
Circulating Water ◽  
Layer Flow

The flow visualization studies around a square cylinder (upstream) and a circular cylinder arranged in tandem configuration is studied experimentally to identify the interference flow patterns. Flow visualization studies are carried out in a re-circulating water channel. The investigations are carried out for tandem arrangement varying the center-to-center distance (L) between the cylinders; L/B ratio is varied from 1 to 5 where B is the characteristic length. Experiments were conduct at a Reynolds number of 2100 (based on B). The results are also obtained for two tandem square cylinder configuration. The flow patterns observed are: Alternate Shear Layer Reattachment with and without gap flow, Simultanous shear layer reattachment and detached shear layer flow pattern. The time of persistence (in percentage) for each flow pattern is estimated over a sufficiently long period of observation time to identify the most influential, predominant flow pattern. Though these patterns are identical for square-square and square-circular tandem configurations, their order of predominance is different for both the configurations.

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 Corner-Arc on the Flow Structures Around a Square Cylinder

2018 ◽  
Author(s):  
Hariprasad Chakkalaparambil Many ◽  
Vishnu Chandar Srinivasan ◽  
Ajith Kumar Raghavan
Keyword(s):  
Drag Reduction ◽  
Oscillation Amplitude ◽  
Water Channel ◽  
Excitation Frequency ◽  
Flow Structures ◽  
Square Cylinder ◽  
Near Wake ◽  
Vortex Size ◽  
Vortex Shedding Frequency ◽  
Visualization Experiments

In this paper, flow structures around a corner modified square cylinder (side dimension, Bo) are presented and discussed. Cylinders with various corner arcs (circular) were considered (arc radius ‘r’). For various Corner Ratios (CR = r/Bo), values ranging from 0 to 0.5, flow visualization experiments were conducted in a water channel and the results are reported at Re = 2100 (based on Bo). Results presented are for two cases (a) stationary cylinders reporting the values of CD (coefficient of drag), St (Strouhal no.), and D (vortex size) and (b) oscillating cylinders at fe/fs = 1 (fe is the cylinder excitation frequency and fs is the vortex shedding frequency) and a/Bo = 0.8 (a is the cylinder oscillation amplitude). The work is aimed to explore the most effective configuration for drag reduction. Cylinder with corner ratio of 0.2 is proved to be the most effective one among the cases considered in this study with 19.3% drag reduction. As a major highlight, in contrast to the results of the previous studies, current study do not reveal a monotonous decrease of drag with increasing corner modification. Instead, it is shown here that, there is a specific value of CR ratio where the drag is the minimum most. A peculiar type of vortex structure was observed in the cases of stationary cylinders with CR > 0.2, contributing to the increase in drag. In the case of oscillating cylinders, description of one complete cycle for all CR ratios at various time instances are presented. The near-wake structures were observed to be dependent on the CR ratio. Counter intuitively, cylinder oscillation does not bring major difference in vortex size compared to the stationary case.

scholarly journals The drag-adjoint field of a circular cylinder wake at Reynolds numbers 20, 100 and 500

2013 ◽  
Vol 730 ◽  
pp. 145-161 ◽  
Author(s):  
Qiqi Wang ◽  
Jun-Hui Gao
Keyword(s):  
Circular Cylinder ◽  
Flow Field ◽  
Unsteady Flow ◽  
Numerical Solutions ◽  
Reynolds Numbers ◽  
Adjoint Equations ◽  
Cylinder Wake ◽  
Near Wake ◽  
Navier Stokes Equation ◽  
D 20

AbstractThis paper analyses the adjoint solution of the Navier–Stokes equation. We focus on flow across a circular cylinder at three Reynolds numbers, ${\mathit{Re}}_{D} = 20, 100$ and $500$. The quantity of interest in the adjoint formulation is the drag on the cylinder. We use classical fluid mechanics approaches to analyse the adjoint solution, which is a vector field similar to a flow field. Production and dissipation of kinetic energy of the adjoint field is discussed. We also derive the evolution of circulation of the adjoint field along a closed material contour. These analytical results are used to explain three numerical solutions of the adjoint equations presented in this paper. The adjoint solution at ${\mathit{Re}}_{D} = 20$, a viscous steady state flow, exhibits a downstream suction and an upstream jet, the opposite of the expected behaviour of a flow field. The adjoint solution at ${\mathit{Re}}_{D} = 100$, a periodic two-dimensional unsteady flow, exhibits periodic, bean-shaped circulation in the near-wake region. The adjoint solution at ${\mathit{Re}}_{D} = 500$, a turbulent three-dimensional unsteady flow, has complex dynamics created by the shear layer in the near wake. The magnitude of the adjoint solution increases exponentially at the rate of the first Lyapunov exponent. These numerical results correlate well with the theoretical analysis presented in this paper.

Sign in / Sign up

Export Citation Format

Share Document