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Velocity characteristics of the flow around a square cross section cylinder placed near a channel wall

Abstract

Laser-Doppler measurements are reported of the flow around a square cross section cylinder placed at various heights (Y 0) above a plane channel wall for a Reynolds number Re H = 1.36 × 104.The thickness of the turbulent boundary layer on the channel wall at the obstacle position, but with it removed from the water tunnel, was equal to 0.8 H, being H the square obstacle height and the free stream turbulence intensity was 6%. The periodic character of the flow in the near wake was characterized by measurements of turbulence spectra in the range 0≤ Y 0/H ≤3.3 and the results revealed that regular vortex shedding was suppressed for a gap height less than 0.35 H. Detailed results of time averaged mean flow properties, turbulence intensities and Reynolds stresses revealed the structural differences of the near wakes with and without vortex shedding for Y O = 0.5 and Y O = 0.25 respectively.

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Abbreviations

R e :

Reynolds number Re = U 0 H/v

H :

Square obstacle height

Y :

Normal coordinate

Y 0 :

Gap distance between the plane wall and obstacle face

C f :

Skin friction coefficient

k :

Turbulent kinetic energy

u τ :

Friction velocity

δ :

Turbulent boundary layer thickness

y + :

Non-dimensional log law coordinate

X r :

Separated flow length behind the obstacle

U :

Mean axial velocity

V :

Mean radial velocity

u2 :

Axial turbulent stress

ν2 :

Normal turbulent stress

uν′ :

Turbulent shear stress

U 0 :

Mean bulk velocity

E :

Power spectrum energy

f :

Predominant frequency

h :

Distance between inner shear layers behind the obstacle

s :

Distance from the wall to the shear layer behind the obstacle

C D :

Drag coefficient

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Durão, D.F.G., Gouveia, P.S.T. & Pereira, J.C.F. Velocity characteristics of the flow around a square cross section cylinder placed near a channel wall. Experiments in Fluids 11, 341–350 (1991). https://doi.org/10.1007/BF00211788

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Keywords

  • Vortex
  • Boundary Layer
  • Reynolds Number
  • Turbulence Intensity
  • Reynolds Stress