Experimental investigation of the fluid dynamic behavior over a sphere and an icosahedron under extremely low Reynolds number conditions

In recent investigations a new kind of instability has been discovered. This instability takes place on spherical beacons placed on the guard cables of the electrical power lines, consisting in instability intermittency states on the aerodynamic lateral force. The before mentioned investigation showed that both the sphere with and without cable exhibit intermittency states. Its behavior is determined by the asymmetry on the boundary layer separation line on the body and is completely random since the sphere is a revolution body with no favored direction. The aim of this work is to investigate the fluid dynamics of a sphere and an icosahedron at low Reynolds numbers using a water tunnel, to establish a comparison between the wake vortexes of a revolution bluff body and a bluff body with sharp edges. Specifically, photos were taken to observe the flow evolution using ink. This technique was employed to assess the system instability, and to measure the dimension and shape of the wake behind this bluff body. The initial part of the work focused on designing and 3D printing the two geometries. Once completed, the test campaign commenced in the water tunnel, examining the effect of varying the Reynolds numbers. The results obtained from these experiments contribute to understanding flow dynamics in the presence of different geometries and comparing curve bodies with sharp edges bodies behavior. Some conclusions and future jobs will be defined.