層流境界層の中に直立する円柱からのうず放出

抄録

Characteristics of vortex formed behind a circular cylinder placed in a laminar boundary layer have been investigated experimentally by flow visualization and analysis on fluctuating velocity signals. Three nondimensional paramerers of R_e = U₀d/v(U₀ : freestream velocity, d : cylinder diameter, v : kinematic viscosity), h/δ(h : cylinder height, δ : boundary layer thickness) and h/d govern the flow field. In the present study, h/δ is kept constant to unity, and h/d and R_e were varied. The following new results were obtained: (i) Within the range of R_e=70∼613, separated shear layers from both sides and the free-edge of the cylinder were linked to form an arch-type vortex for h/d up to 4. (ii) At h/d=3 where an arch-type vortex is formed, the Strouhal number S_t(=fd/U₀) against R_e can be classified into three regions based on different time rates of intermittent vortex shedding. (iii) Simiraly, at h/d=6 where Karman-type vortex is formed, S_t against R_e can be classified into two regions.