Analysis Of Von-Kármán Vortex Street Dynamics in Laminar Flow

Abstract

The Von Kármán vortex street is one of the most fundamental and visually striking phenomena in fluid mechanics, arising when flow separates periodically from a bluff body, such as a circular cylinder. This study presents a comparative Computational Fluid Dynamics (CFD) investigation of flow past a 2D circular cylinder at three distinct Reynolds numbers, Re = 20, Re = 200, and Re = 4000, using ANSYS Fluent 2026 R1. Air at standard conditions (ρ = 1.225 kg/m³, μ = 1.80 × 10⁻⁵ Pa·s) was used as the working fluid, and a rectangular computational domain of dimensions 17.5D × 5D was employed, with the cylinder positioned 2.5D from the inlet. The boundary conditions comprised a uniform-velocity inlet, a pressure outlet, and no-slip walls. The laminar solver was applied for Re = 20 and Re = 200, while the k-ω SST turbulence model was adopted for Re = 4000. A grid independence test was conducted to ensure numerical accuracy. Results demonstrate three qualitatively distinct flow regimes: a steady symmetric wake at Re = 20 with no vortex shedding; a well-developed periodic Von-Kármán vortex street at Re = 200 with alternating vortex rows extending far downstream; and a broader, more disorganised turbulent wake at Re = 4000 characterised by rapid wake diffusion. The findings are in good qualitative agreement with published experimental and numerical benchmarks. The Strouhal number for Re = 200 is estimated at approximately St ≈ 0.19, consistent with the Williamson correlation. This work highlights the sensitivity of wake structure to Reynolds number and validates ANSYS Fluent as an effective tool for internal and external flow analysis.