Effects of simple wall-mounted cylinder arrangements on a turbulent boundary layer

Hot-wire measurements were acquired downstream of a single cylinder and single spanwise arrays of cylinders with height-to-diameter ratioH/D = 1:5. The tops of the cylinders were located near the top of the logarithmic region (z/δ = 0:13, z⁺ = 150) in a turbulent boundary layer with Re_τ = 1200. Two additional tests used cylinders of half the original diameter with tops located at z⁺ = 150 and 100. Measurements included velocity profiles and frequency spectra up to 12 diameters downstream. The single cylinder yielded a mean velocity deficit that extended from z ⁺ = 20 to 200 and a redistribution of the root-mean-square velocity away from the wall toward the top of the cylinder with a corresponding increase in the power spectral density over a broad frequency range. Cylinder arrays with 3D and 6D spanwise spacing yielded significant wake interactions producing mean velocity deficits and rms values greater than those observed at equivalent distances downstream of a single cylinder. The largest mean deficits and root-mean-square velocities occurred in the log region at midspacing between cylinders. No dominant frequency was observed in these regions; however, a significant spectral peak was observed in the wake of a single cylinder. Significant wake interaction effects extended to the top of the log region but not beyond.