Experimental investigation on wake behind a wavy cylinder having sinusoidal cross-sectional area variation

Turbulent wake behind a cylinder having sinusoidal variation in cross sectional area along the span is investigated experimentally. The drag force, mean velocity and turbulence intensity profiles of the wake behind the cylinder are measured for Reynolds numbers based on the mean diameter Dm in the range of Re=5×103-2×104. Two sinusoidal cylinder models are tested, model 1 with λ/D=1 and model 2 with λ/D=2 (λ is pitch of the cylinder). Flow pattern around the cylinders is visualized using the particle tracing method and the smoke-wire technique. The experimental results are compared with those obtained for a smooth cylinder having the equivalent diameter. At Re=104, for the case of model 2 the drag coefficient is reduced about 22%, compared with the smooth cylinder. The wake structure shows periodic variation in the spanwise direction. The wake width expands in the region behind saddles of cylinder and shrinks behind nodes of the cylinder. The vortex formation region is elongated and the vortex-induced fluctuations are suppressed, reducing drag acting on the cylinder. The visualized flow shows strong interaction between the three-dimensional geometry of cylinders and vortex structure in the near wake.