Coanda effect or wall-attachment effect, the tendency of a moving fluid, either liquid or gas, to attach itself to a surface and flow along it. As a fluid moves across a surface a certain amount of friction (called “skin friction”) occurs between the fluid and the surface, which tends to slow the moving fluid. This resistance to the flow of the fluid pulls the fluid towards the surface, causing it stick to the surface. Thus, a fluid emerging from a nozzle tends to follow a nearby curved surface—even to the point of bending around corners—if the curvature of the surface or the angle the surface makes with the stream is not too sharp. Discovered in 1930 by Henri Coanda, a Romanian aircraft engineer, the phenomenon has many practical applications in fluidics and aerodynamics.
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