Coanda

Coanda refers to a fluid dynamics principle and to the Romanian inventor associated with its discovery. The Coanda effect describes the tendency of a fluid jet to attach to and follow a nearby curved surface. This behavior results from viscous forces that entrain surrounding fluid and from pressure differences created as the jet flows along the surface. The effect explains how a jet can cling to a contour and then detach when conditions change.

Henri Coandă (1886–1972), a Romanian inventor and aviation pioneer, described the phenomenon in the early 20th century. In 1910–1911 he conducted experiments with a jet of air issued near a curved surface and observed that the jet tended to cling to the surface. His observations contributed to early ideas about jet propulsion and aerodynamics. The phenomenon bears his name, though later fluid dynamics theories have refined the scientific explanation.

Applications and implications: In engineering, the Coanda effect is leveraged in devices such as flow-control actuators, jet diffusers, air intakes, and some thrust-vectoring concepts. In microfluidics and biomedical devices, the principle helps manipulate small fluid streams. In practice, the jet adheres to a surface only within certain distances and curvatures; separation can occur due to adverse pressure gradients or high jet momentum.

The term Coanda effect is widely used in fluid mechanics literature to describe this jet-surface interaction. It remains a foundational example in the study of boundary layer entrainment, attachment, and deflection of flows.