# The turbulent flow field around a circular cylinder

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## Abstract

The flow field around a circular cylinder mounted vertically on a flat bottom has been investigated experimentally. This type of flow occurs in several technical applications, e.g. local scouring around bridge piers. Hydrogen bubble flow visualization was carried out for Reynolds numbers ranging from 6,600 to 65,000. The main flow characteristic upstream of the cylinder is a system of horse-shoe vortices which are shed quasi-periodically. The number of vortices depends on Reynolds number. The vortex system was found to be independent of the vortices that are shed in the wake of the cylinder. The topology of the separated flow contains several separation and attachment lines which are Reynolds number dependent. In the wake region different flow patterns exist for each constant Reynolds number.

## Keywords

Vortex Reynolds Number Flow Field Fluid Dynamics Pier## List of symbols

*B*width of flume

*b*_{0}wake width

*C*_{d}drag coefficient

*C*_{f}coefficient of skin friction

*C*_{p}pressure coefficient

*D*cylinder diameter

*K*_{s}bed roughness

*L*_{E}integral length scale

*Re*Reynolds number based on

*Ym**Re (D)*Reynolds number based on

*D**Re(l)*Reynolds number based on length

*U*free stream velocity

*Um*mean flow velocity

*U*_{s, max}maximum velocity deficiency

*u*streamwise velocity

*u*_{*}shear velocity

*X, Y, Z*cartesian co-ordinate system measured from the cylinder centre

*X, Y, Z*longitudinal, vertical and lateral directions

*Ym*mean flow depth

*δ*boundary layer thickness

*Γ*circulation

*δ*_{d}displacement thickness

*θ*momentum thickness

*λ*_{f}dissipation length scale

*ν*kinematic viscosity

*Ω*vorticity

*τ*shear stress

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