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Re: "How Things Work" Website



On Sat, 29 Mar 1997, William Beaty wrote:

On Sat, 29 Mar 1997, John Mallinckrodt wrote:

I'm curious about why you call the "airstreams must join at the trailing
edge" argument "false." In the steady state, laminar flow regime in which
the Bernoulli principle holds (and which is, admittedly, questionable for
airplane wings) mustn't this be the case?

Nope. I'm not sure, but I suspect that in some 2D simplifications, the
parcels of air may indeed be required to rejoin at the trailing edge. If
so, then this is an artifact of the simplifying assumptions, not a feature
of real airfoils. In real 3D wings there is a sort of singularity trailing
behind the wing, called a "vortex sheet" by aerodynamics textbooks.
...

But doesn't this just support my point? After all, the existence of
vortices technically rules out the use of Bernoulli's principle. The
streamline photos you attached certainly do seem to be graphic proof that
the airstreams do not meet at the trailing edge.

John
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A. John Mallinckrodt email: mallinckrodt@csupomona.edu
Professor of Physics voice: 909-869-4054
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