Cylinderväckt

Cylinderväckt (cylinder wake) describes the flow pattern downstream of a cylindrical body in a fluid. When a cylinder is placed in a steady crossflow, the fluid splits around the sides, and the separated shear layers roll up into alternating vortices, creating a characteristic wake known as a Von Kármán vortex street. The wake’s behavior depends on the Reynolds number Re = UL/ν, where U is the flow speed, L the cylinder diameter, and ν the kinematic viscosity.

For moderate Re, the wake is time-periodic with a shedding frequency f related to U and L by the Strouhal number St = fD/U, typically around 0.2 across many cylinders. At lower Re the wake is steady and symmetric; at higher Re it becomes unsteady and eventually turbulent. The wake influences drag on the cylinder and can induce vortex-induced vibrations in flexible or anchored cylinders, a concern for bridges, chimneys, offshore pipelines, and tall structures.

Studying cylinderväckt involves flow visualization (smoke, dye) and quantitative techniques such as hot-wire anemometry, particle image velocimetry (PIV), or laser Doppler velocimetry (LDV). Computational fluid dynamics (CFD) models are widely used to explore wake interactions, end effects, and arrangements of multiple cylinders.

In Swedish-language contexts, cylinderväckt is often used as a direct reference to the cylinder wake concept, though terminology may vary by discipline. The topic remains foundational in fluid mechanics and engineering design against vibration, noise, and fatigue.