✓ Sources checked · 10 September 2026 · View verification
The Coandă effect describes attachment of a jet to a nearby surface, including a suitably curved wall. Pressure gradients and entrainment help turn the jet; attachment is not a rule that all fluids must follow every curve.
By Matan · Updated
Turning requires a force
A jet entrains surrounding fluid. A nearby wall alters that entrainment and pressure field, and a transverse pressure gradient can supply the acceleration needed for curved streamlines. Viscosity and turbulent mixing influence attachment and eventual separation. [1]
Worked momentum change for a turned jet
Consider an idealized jet with mass flow 0.020 kg/s and speed 30 m/s, turned from horizontal to 90° downward without changing speed. Momentum balance gives force on the jet (−0.60, −0.60) N if right and up are positive and other boundary forces are negligible. The equal reaction on the turning assembly has magnitude √(0.60² + 0.60²) = 0.849 N.
The calculation does not predict attachment
This example assumes the turn has already occurred. It quantifies the resulting momentum change, not the maximum angle a particular nozzle can sustain. Pressure forces at inlet and outlet and entrained mass must be included in a real control-volume calculation.
Avoid an all-purpose explanation of lift
Blown lifting surfaces can exploit attached jets, but ordinary wing lift needs the complete flow and pressure field. Symmetric wings can generate lift at nonzero angle of attack. Jet attachment is also not a universal explanation for inkjet droplet steering or engine thrust.
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How this article was checked
Sources checked; calculations checked where shown. Main claims and model assumptions were checked against the references below. Example arithmetic and units were checked separately. Numerical examples are illustrative calculations, not experimental measurements.
Source checking and editing assisted by AI. No independent human scientific review is recorded for this revision. This record applies to the version dated 10 September 2026.
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Sources and further reading
Cite this article
Matan. “Coanda effect in fluid dynamics.” Your Physicist. Originally published 2023-05-17; updated 2026-09-10. https://your-physicist.com/coanda-effect-in-fluid-dynamics/
Revision history
10 September 2026: Replaced energy-minimization and universal wing/inkjet claims with jet attachment and momentum balance. Added references and a transparent verification record.
