Boundary Layer Investigations for Primarily Axial Flow Over a Stationary and Transversely Oscillating Cylinder

摘要

Boundary layer information local to three longitudinal positions has been characterized for a 122 cm long acrylic cylinder with hemispherical endcaps, via analysis of stereo particle image velocimetry (PIV) measurements made during laterally oscillating motions and for steady, axisymmetric flow. No obvious turbulent flow structures or indications of boundary layer separation were observed at nonzero advance speeds, and skin friction coefficients were subsequently estimated for magnitude relative to the dynamic pressure associated with an axial flow speed of 0.25 m/s. Computational fluid dynamics (CFD) analysis is performed in commercial software to accompany the experimental measurements. Local skin friction coefficients are estimated and deviate, on average, from analytical solutions for zero gradient axisymmetric flows by around 22% and from the accompanying numerical solutions by around 4%. The effects of intermittent boundary layer compression and turbulence inhibition are readily observed for the oscillating cylinder, although vortex shedding is observed for some large amplitude, high frequency cases.