Pyörteekerroitus

Pyörteekerroitus, often translated as vortex shedding or vortex street, is a phenomenon in fluid dynamics where vortices are generated alternately from each side of a bluff body. When a fluid flows past an obstacle, such as a cylinder or a flat plate, the flow separates from the surface of the body. This separation leads to the formation of swirling regions of fluid called vortices. Due to the unsteady nature of the flow and the instability of the separated shear layers, these vortices are shed periodically from the upstream edge of the body.

The alternating nature of the shedding results in a staggered pattern of vortices downstream of the object, forming what is known as a von Kármán vortex street. This phenomenon is characterized by a specific frequency at which the vortices are shed, which is dependent on the flow velocity, the size and shape of the bluff body, and the fluid's properties (viscosity and density). This relationship is often described by the Strouhal number, a dimensionless quantity.

Pyörteekerroitus has significant implications in various engineering applications. For instance, it can cause vibrations in structures like bridges, chimneys, and heat exchanger tubes, potentially leading to fatigue failure. Understanding and predicting vortex shedding is crucial for designing these structures to withstand such dynamic loads. Conversely, the phenomenon can also be harnessed for beneficial purposes, such as in vortex-induced vibration power generation systems, where the energy of the oscillating vortices is converted into electricity. The formation of a vortex street is a common sight in nature, seen in the wake of rocks in a stream or the flow around a bird's wing.