自然対流によって低レイノルズ数で発生するカルマン渦列の可視化  [in Japanese] Visualization of the Karman Vortex Street Generated at Low Reynolds Numbers Due to Natural Convection  [in Japanese]

A wake below a heated circular cylinder submerged in a downward mainstream of air at a low Reynolds number is visualized by both numerical calculation and smoke-wire experimentation. Numerical results show that the filament in the isothermal wavy wake becomes round and spiral, its scale increases, and a Karman vortex street is generated with an increase in negative buoyancy. Experimental results agree well with numerical results. The wake patterns observed at 44≦Re≦60 correlate well with Ri/Re^<1/3>=A, where Re is the Reynolds number, Ri the Richardson number, and A the degree of opposing flow. The critical Richardson number for the generation of the Karman vortex street due to negative buoyancy is Ri_crit/Re^<1/3>=0.025. With an increase in cylinder temperature, the Strouhal number and the vortex velocity decrease gradually, and the wake width increases gradually.