What triggers the breakdown of familiar vortex patterns behind a cylinder? This study investigates the "second wake transition," a phenomenon occurring far downstream from a bluff body where the well-known Bénard–von Kármán vortex street gives way to a secondary vortex street with a lower frequency. The research focuses on characterizing the onset of this transition within a specific range of Reynolds numbers using a nearly two-dimensional soap film flow, bridging experimental observation and numerical simulation. The authors meticulously measure the dimensionless distance between the cylinder and where the second wake begins, revealing an inverse relationship with the Reynolds number, consistent with a Re−1/2 power law. These experimental findings are then validated through two-dimensional far-wake numerical simulations, showing a strong agreement between the observed and predicted behavior. This rigorous approach combines practical experimentation with advanced computational methods. The research contributes valuable insights into fluid dynamics, particularly the behavior of wakes behind obstacles, offering a deeper understanding of complex flow phenomena. This work has implications for fields ranging from aerodynamics to the design of structures interacting with fluid flows.
As a publication in Physics of Fluids, this paper contributes directly to the understanding of fundamental fluid dynamics. Its focus on the Reynolds number and wake transitions aligns with the journal's scope, adding to the body of knowledge concerning fluid behavior and its applications in engineering and physics.