> I choose not to teach the circulation theory to my students because I
> don't think it exists in the manner the term suggests it does. I
> understand
> what people are trying to explain by using the term "circulation"
> (basically
> upwash and downwash),
Circulation theory of lift and upwash/downwash are different things. A 2D
airfoil doesn't have any upwash but still has circulation.
> but because the airflow does not circulate completely
> around the wing in a uninterupted circular fa****on round and round (it
> stops
> at the stagnation points on the leading and trailing edges) I personally
> think the term "circulation" is misleading and even confusing.
You only need circulation theory when you assume inviscid flow.
Circulation
theory can't be explained with physical intuition because it's not a
physical thing...it's a math trick put in to correct for the fact that
you're ignoring viscosity, compressibility, time-variance, and a bunch of
other stuff to try to simplify the Navier-Stokes equations.
> I am no engineer, but my current opinion is that Bernoulli's theory
> only
> explains how the airflow accelerates over the top of the wing AS A
RESULT
> OF
> the reduced pressure. Not vice versa.
Correct. In order to get a stable flow field around the airfoil, you have
to have a low pressure area near the back of the wing. Bernoulli
correctly
describes what's happening to the streamline, but isn't the cause.
> The reduced pressure over the upper surface, caused by a positive angle
> of attack, causes the airflow to accelerate and the airflow's
> viscosity/coanda effect causes it to follow the upper surface beyond the
> trailing edge where the high velocity airflow continues off the wing in
a
> downward motion in the form of the downwash which lifts the airplane.
Coanda effect doesn't cause anything...it's a description (like
Bernoulli),
not a cause. Viscocity doesn't do it either (the air is not "stuck" to
the
wing). It's the pressure field that causes the air to follow the airfoil
surface.
> What do you all engineers think of the site?
It's pretty good. Better than most I've seen. It does make some physical
whoopsies (you can't pull on air, for example): "Air is pulled from
above".
It's explanation of the Coanada effect is completely bogus. They use the
illustration of water flowing over a glass...this looks like the Coanada
effect, but the physical are totally different. Air does not stick to the
airfoil surface.
Tom.
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