The Coanda Effect (so named after Henri-Marie Coanda) relates to the phenomenon whereby a fluid stream tends to follow the profile of the bounding surface providing that the divergence doesn't get too silly .. not really related to this question.
Without getting into arguments of semantics, fluid forces basically relate to what happens if we can get a fluid to move .. in making it move, we need to exert a force (generally achieved by pressures acting over a surface) and we can get a reaction (sometimes referred to as a psuedo-force for reasons beyond me) which might be of use to us .
Aim is to maximise the useful force component (lift in aircraft-speak .. ie a force normally acting in a direction pendicular to the direction of flight) while giving away as little as we can to the undesirable bit (drag .. acting parallel to flight and requiring power to offset).
This exercise can be achieved by
(a) sticking anything into the wind .. bit like putting one's hand out of the car window .. depending on orientation, the perceived force can be varied from all drag to a useful amount of lift with an attendent drag penalty .. not too effective, though
(b) sticking a suitably shaped surface into the wind .. otherwise called a wing .. the aerodynamicist's black art is to maximise the desirable while minimising the undesirable
(b) spinning a body in the wind .. if we use a cylinder, for instance, very high lift forces can be generated .. this is a pretty stock standard undergraduate wind tunnel demo exercise in first year aerodynamics ...
We can also get the same sort of effect with a sphere (cricket ball etc) and this is the black art of our illustrious (if somewhat subject to media harassment for the odd peccadillo) Warney and his spin colleagues.
(c) manipulating laminar and turbulent flow separation to give a nett lateral force resulting from the different forces associated with the two sorts of flow. This is the alternative black art of the fast bowler who gets a good deal of swing in the delivery of the ball.
Ah .. fond memories of playing about in wind tunnels as a youngster ...
Last edited by john_tullamarine; 5th Oct 2005 at 01:52.