"[2] It is named after Romanian inventor Henri Coandă, who was the first to recognize the practical application of the phenomenon in aircraft design around 1910.
The motor-driven turbine pushed hot air rearward, and Coandă noticed that the airflow was attracted to nearby surfaces.
[4][5] This name was accepted by the leading aerodynamicist Theodore von Kármán, who had a long scientific relationship with Coandă on aerodynamics problems.
The resultant forces from this low pressure tube end up balancing any perpendicular flow instability, which stabilises the jet in a straight line.
[10] Early sources provide theoretical and experimental information needed to derive a detailed explanation of the effect.
On the left image of the preceding section: "The mechanism of Coandă effect", the effect as described, in the terms of T. Young as "the lateral pressure which eases the inflection of a current of air near an obstacle", represents a free jet emerging from an orifice and an obstacle in the surroundings.
It includes the tendency of a free jet emerging from an orifice to entrain fluid from the surroundings confined with limited access, without developing any region of lower pressure when there is no obstacle in the surroundings, as is the case on the opposite side where turbulent mixing occurs at ambient pressure.
[11][12] Above a critical h/r ratio of 0.5 only local effects at the origin of the jet are seen extending over a small angle of 18° along the curved wall.
A calculation made by Woods in 1954[13] of an inviscid flow along a circular wall shows that an inviscid solution exists with any curvature h/r and any given deflection angle up to a separation point on the wall, where a singular point appears with an infinite slope of the surface pressure curve.
Introducing in the calculation the angle at separation found in the preceding experiments for each value of the relative curvature h/r, the image here was recently obtained,[14][self-published source?]
and shows inertial effects represented by the inviscid solution: the calculated pressure field is similar to the experimental one described above, outside the nozzle.
According to Van Dyke,[15] as quoted in Lift, the derivation of his equation (4c) also shows that the contribution of viscous stress to flow turning is negligible.
An alternative way would be to calculate the deflection angle at which the boundary layer subjected to the inviscid pressure field separates.
Moreover, in the case of a free jet the equation can be solved in closed form, giving the distribution of velocity along the circular wall.
In this last case which is the geometry proposed by Coandă, the claim of the inventor is that the quantity of fluid entrained by the jet from the surroundings is increased when the jet is deflected, a feature exploited to improve the scavenging of internal combustion engines, and to increase the maximum lift coefficient of a wing, as indicated in the applications below.
Closely following the work of Coandă on applications of his research, and in particular the work on his "Aerodina Lenticulară,"[19] John Frost of Avro Canada also spent considerable time researching the effect, leading to a series of "inside out" hovercraft-like aircraft from which the air exited in a ring around the outside of the aircraft and was directed by being "attached" to a flap-like ring.
This is, as opposed to a traditional hovercraft design, in which the air is blown into a central area, the plenum, and directed down with the use of a fabric "skirt".
Two prototypes were built as "proof-of-concept" test vehicles for a more advanced U.S. Air Force fighter and also for a U.S. Army tactical combat aircraft requirement.
The Shin Meiwa US-1A flying boat utilizes a similar system, only it directs the propwash from its four turboprop engines over the top of the wing to generate low-speed lift.
More uniquely, it incorporates a fifth turboshaft engine inside of the wing center-section solely to provide air for powerful blown flaps.
A better understanding of Coandă effect was provided by the scientific literature produced by ACHEON EU FP7 project.
[29][30] A practical use of the Coandă effect is for inclined hydropower screens,[31] which separate debris, fish, etc., otherwise in the input flow to the turbines.
[38] In Formula One automobile racing, the Coandă effect has been exploited by the McLaren, Sauber, Ferrari and Lotus teams, after the first introduction by Adrian Newey (Red Bull Team) in 2011, to help redirect exhaust gases to run through the rear diffuser with the intention of increasing downforce at the rear of the car.
[39] Due to changes in regulations set in place by the FIA from the beginning of the 2014 Formula One season, the intention of redirecting exhaust gases to use the Coandă effect have been negated, due to the mandatory requirement that the car exhaust not have bodywork intended to contribute to aerodynamic effect situated directly behind it.
[41][42] The Coandă effect can be demonstrated by directing a small jet of air upwards at an angle over a ping pong ball.
This demonstration can be performed using a hairdryer on the lowest setting or a vacuum cleaner if the outlet can be attached to the pipe and aimed upwards at an angle.
Another demonstration is to direct the air flow from, e.g., a vacuum cleaner operating in reverse, tangentially past a round cylinder.