Coanda Effect

Coanda effect is the phenomena in which a jet flow attaches itself to a nearby surface and remains attached even when the surface curves away from the initial jet direction.

In free surroundings, a jet of fluid entrains and mixes with its surroundings as it flows away from a nozzle.

When a surface is brought close to the jet, this restricts the entrainment in that region. As flow accelerates to try balance the momentum transfer, a pressure difference across the jet results and the jet is deflected closer to the surface - eventually attaching to it.

Even if the surface is curved away from the initial direction, the jet tends to remain attached. This effect can be used to change the jet direction. In doing so, the rate at which the jet mixes is often significantly increased compared with that of an equivalent free jet.


The phenomena derives its name from a Romanian born aeronautical engineer - Henri Coanda.

He built an early form of jet propelled aircraft and found that the exhaust attached to the fabric of the fuselage causing it to catch fire and crash.

Many devices use Coanda effect. One notable application of the Coanda effect is the NOTAR™ helicopter.

Coanda effect forms the basis of much of S & C Thermofluids' innovative in-house research programme. To date, successful devices and granted patents have included:

  • A compressed air powered ejector
  • A jet pump shower nozzle
  • A catalytic converter exhaust system
  • The high speed delivery of chocolate from a trough
  • Flow deflection devices

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S & C Thermofluids Ltd

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