Coanda effect

The Coandă effect (/ˈkwɑːndə/ or /ˈkwæ-/) is the tendency of a fluid jet to stay attached to a convex surface. A better definition has been provided by Henri Coandă in different patents and have been reported by Merriam Webster dictionary: "the tendency of a jet of fluid emerging from an orifice to follow an adjacent flat or curved surface and to entrain fluid from the surroundings so that a region of lower pressure develops." The pressure effect, which is usually not indicated, is fundamental for the comprehension of the Coandă effect.

The principle was named after Romanian aerodynamics pioneer Henri Coandă, who was the first to recognize the practical application of the phenomenon in aircraft development.

An early description of this phenomenon was provided by Thomas Young in a lecture given to The Royal Society in 1800:

The lateral pressure which urges the flame of a candle towards the stream of air from a blowpipe is probably exactly similar to that pressure which eases the inflection of a current of air near an obstacle. Mark the dimple which a slender stream of air makes on the surface of water. Bring a convex body into contact with the side of the stream and the place of the dimple will immediately show the current is deflected towards the body; and if the body be at liberty to move in every direction it will be urged towards the current...

A hundred years later, Henri Coandă identified an application of the effect during experiments with his Coandă-1910 aircraft, which mounted an unusual engine he designed. The motor-driven turbine pushed hot air rearward, and Coandă noticed that the airflow was attracted to nearby surfaces. In 1934 Coandă obtained a patent in France for a "method and apparatus for deviation of a fluid into another fluid." The effect was described as the "deviation of a plain jet of a fluid that penetrates another fluid in the vicinity of a convex wall." The first official documents that explicitly mention the Coandă effect were two 1936 patents by Henri Coandă. This name was accepted by the leading aerodynamicist Theodore von Kármán, who had with Coanda a long scientific relationship on aerodynamics problems.

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