Yasutake Haramoto

Visualization of Three-Dimensional Flow Structures in the Wake of an Inclined Circular Cylinder

In the previous measurements of the aerodynamic sound generated from an inclined circular cylinder, it is reported that the sound pressure level (SPL) changes with the aspect ratio and the inclined angle. Therefore, we have investigated the changes in the vortex structure of the wake considered as one of the causes of the SPL variation. Using the low-noise wind tunnel, the velocity fluctuation in the wake is measured to obtain the correlation length. Moreover, the flow visualization is performed with a hydrogen bubble method and a numerical analysis method in order to clarify how the wake structure changes by variations of aspect ratio and inclined angle. As a result of this investigation, it is shown that the spanwise structure of Karman’s vortex is highly influenced by the interference of Karman’s vortex with the bottom endplate, and that the influence on the spanwise structure in the wake becomes greater as the aspect ratio decreases and the inclined angle increases.

Aerodynamic Noise and Flow Visualization Around an Inclined Circular Cylinder

We measured the aerodynamic noise generated from an inclined circular cylinder with endplates in experimental conditions using a low noise wind tunnel. The inclination-angle dependency of the aerodynamic sound is related to the aspect ratio A that is the ratio of the distance between the endplates to the circular cylinder diameter. To analyze the dependency in detail we derived the correlation length from the velocity fluctuation in the wake. As a result, when the inclined angle changed from 0 degrees to 20 degrees, the correlation length got smaller at A = 10. On the other hand, in the case of A = 30, the correlation length got longer. So we visualized the flow around the cylinder using numerical simulation and the hydrogen bubble method in order to analyze these phenomena.Copyright