Wake Characteristics of Sphere with Circular Uniaxial Through-Hole Arranged Perpendicularly to Streamwise Direction

In this study, the wake characteristics of a sphere with a uniaxial through-hole (that is, vented sphere) and that of a sphere without a through-hole (that is, basic sphere) are investigated to clarify the effect of the uniaxial through-hole on the vortex shedding in the wake. A sphere with a diameter of 25.4 mm having a 6 mm circular uniaxial through-hole was fixed to the test section of the wind tunnel and arranged perpendicularly to the streamwise direction. Results show that the vented sphere stabilizes the vortex shedding. A dominant peak at f = 55 Hz is observed in the wake of the vented sphere, whereas a convex peak over a wide range of 40 < f < 70 Hz is observed in the wake of the basic sphere. In addition, the Reynolds stress in the wake of the vented sphere takes a constant value, whereas it attenuates as the flow moves toward the downstream direction for the basic sphere. The cause of these differences in the Reynolds stress is explained using the co-spectrum of the streamwise and spanwise velocity fluctuations. In the wake of the basic sphere, the negative co-spectrum peak over a wide range of 40 < f < 70 Hz attenuates as the flow moves toward the downstream direction. In