VELOCITY CHARACTERISTICS OF THE FLOW AROUND A SQUARE CROSS-SECTION CYLINDER PLACED NEAR A CHANNEL WALL

Laser-Doppler measurements are reported of the flow around a square cross section cylinder placed at various heights (Y0) above a plane channel wall for a Reynolds number Re(H) = 1.36 x 10(4). 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 less-than-or-equal-to Y0/H less-than-or-equal-to 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 Y0/H = 0.5 and Y0/H = 0.25 respectively.