Hot Air, and Compressibilty
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Hot Air, and Compressibility
A’course air is compressible, and so is water. Any kid who fools around with bicycle pump or a shock absorber, and believes what he sees, rather than what he is told, can feel the compressibility. But, but, but, at modest speeds free air will NOT compress and prefers to “run away” rather than doing so. For example, if you sweep your hand through the air, the flow runs away and, although the pressure on your palm is higher than static, there is virtually no compression of the fluid. You have to sweep your hand at a speed comparable to that of sound (about 330 m/s here on earth) in order stop the air from getting away and to achieve any compression. Since, according to my latest studies on musculature, the maximum speed of an Olympic discus hurler is about 33 m/s, we’re not likely to experience that. Anyhow, the effective incompressibility of air is taught Day 1 in Aerodynamics 101! The reason WHY is reserved for four years later in grad school! Surely anyone who can read today has heard of the “sound barrier” or seen the movie, if you can’t read. Many folks in the West have experienced a sonic boom. All this has been known since 1890 and was described, analyzed and measured by Herr Doktor Ernst Mach, a product of that golden milieu of scientific thinkers, the old Austro-Hungarian Empire. Mach was a rare bird, being an intelligent philosopher who discussed physics with Einstein. He didn’t agree with Special Relativity. Wrong there, Ernie! Some people have heard of his number – certainly all test pilots. I instructed many in the Navy. I painfully learned this stuff, and used the instrument Mach invented, the Schlieren, in my early days as a grad student, battling with shock waves in a grimy subterranean Wizard’s Cave, the Hypersonics Lab, not at, but underneath Caltech! All the above info I stand behind, and have published on. It’s not conjecture or anecdote. I don’t discuss things I don’t understand. Like most scientists, I am an ignorant fellow, oblivious to the vast majority of human knowledge, but enjoy being enlightened by folks who do know. It is not dumb not to know things, but it is to think that your own knowledge encompasses physical truth on subjects on which you are ignorant. Peter Lissaman, Da Vinci Ventures Expertise is not knowing everything, but knowing what to look for. 1454 Miracerros Loop South, Santa Fe, New Mexico 87505,USA tel:(505)983-7728 ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org |
Re: Hot Air, and Compressibilty
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[hidden email] wrote:
> > You have to sweep your hand at a speed comparable to that of sound > (about 330 m/s here on earth) in order stop the air from getting away > and to achieve any compression. > Ok, so in one of the articles mentioned, http://physicsworld.com/cws/article/news/40993 ..it said.. "What they found was that a staggered column of alternately clockwise- and anticlockwise-rotating turbines significantly enhances the speed of turbine rotation. The reason, they say, is that the presence of neighbouring turbines concentrates and accelerates the wind." The term `concentrate', to me, sounds like a synonym of `compress' but in any case `accelerate' could be true in any case. The authors of the work are Caltech aerodynamics guys, so if all you'll give us is, "Shut up and trust the experts", well... Is their claim impossible? Marcus ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org |
Re: Hot Air, and Compressibilty
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In reply to this post by plissaman
Yes. And while we are at it, what does it mean when meteorologists say
that air is more dense near the surface than higher up, or that cold air is denser than warm? N Nicholas S. Thompson Emeritus Professor of Psychology and Ethology, Clark University ([hidden email]) http://home.earthlink.net/~nickthompson/naturaldesigns/ http://www.cusf.org [City University of Santa Fe] > [Original Message] > From: Marcus G. Daniels <[hidden email]> > To: The Friday Morning Applied Complexity Coffee Group <[hidden email]> > Date: 11/27/2009 11:21:15 PM > Subject: Re: [FRIAM] Hot Air, and Compressibilty > > [hidden email] wrote: > > > > You have to sweep your hand at a speed comparable to that of sound > > (about 330 m/s here on earth) in order stop the air from getting away > > and to achieve any compression. > > > Ok, so in one of the articles mentioned, > > http://physicsworld.com/cws/article/news/40993 > > ..it said.. > > "What they found was that a staggered column of alternately clockwise- > and anticlockwise-rotating turbines significantly enhances the speed of > turbine rotation. The reason, they say, is that the presence of > neighbouring turbines concentrates and accelerates the wind." > > The term `concentrate', to me, sounds like a synonym of `compress' but > in any case `accelerate' could be true in any case. > > The authors of the work are Caltech aerodynamics guys, so if all you'll > give us is, "Shut up and trust the experts", well... > > Is their claim impossible? > > Marcus > > > > > > > > > > ============================================================ > FRIAM Applied Complexity Group listserv > Meets Fridays 9a-11:30 at cafe at St. John's College > lectures, archives, unsubscribe, maps at http://www.friam.org ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org |
Re: Hot Air, and Compressibilty
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NASA have got a Beginner's Guide to Aeronautics that's worth looking at. It's includes a section on compressible aerodynamics, which - as Peter points out - is not the regime that these turbines are operating in (as object speeds are much lower than speed of sound).
-- R P.S. Nick - meteorologists are saying just what you think they are: a cubic meter of air down here has a higher mass than a cubic meter of air up there. That NASA site has an interactive demo called Gaslab (at bottom here) that enables you to explore the ideal gas law. On Fri, Nov 27, 2009 at 11:30 PM, Nicholas Thompson <[hidden email]> wrote: Yes. And while we are at it, what does it mean when meteorologists say ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org |
Re: Hot Air, and Compressibilty
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In reply to this post by plissaman
Look, I know I'm wrong here, but ....
Doesnt greater density imply compression?
N
Nicholas S. Thompson
Emeritus Professor of Psychology and Ethology,
Clark University ([hidden email])
http://www.cusf.org [City University of Santa Fe]
============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org |
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