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-   -   'one from the vault' - no laminar/turbulent transition? (http://www.cfd-online.com/Forums/main/102575-one-vault-no-laminar-turbulent-transition.html)

Mentor Sproxie May 29, 2012 03:24

'one from the vault': no (anomalous) laminar-turbulent transition 'discrepancy'
 
Re: [AT LEAST and...especially] THE ONCE CONTROVERSIAL LAMINAR-TURBULENT TRANSITION 'DISCREPANCY': SMALLER vs. LARGER DIAMETER TUBES?
This 'one from the vault,' so to speak, is enough to put me in a quandry...how do I deal with it? It's hard to know where to start! I guess this is more or less a cry for help - by putting it up for discussion amongst those who feel qualified to take it on board and to throw further light on these things. I'll hopefully learn SOMETHING further, by watching for future discussion amongst those of you with the precise expertise to be able to offer such insights.
It's a website featuring a (now deceased) Australian physiologist presenting (in compilation form) his challenging views, deriving from work undertaken in the period: 1970s through 2000s, on the validity (or 'otherwise') of THE laminar-turbulent transition 'discrepancy' which had been said to exist in small diameter tubes:
www.newdirectionforfluiddynamics.com
It's a seemingly compelling revision, even if only because of the existence of a University of Pennsylvania (2004) publication's findings in a similar vein:
www.springerlink.com/index/HTDL66WLLA80T0QP.pdf or look for key words/entitled: 'The Transition from Laminar to Turbulent Flow in Liquid Filled Microtubes'.
Both these 'sources' seem, ultimately, to concur in their respective concluding remarks that there is apparently NO DIFFERENCE (after all) in the behaviour of flow in tiny vessels, with a diameter no larger than a human hair, when compared with that found in ones that are inordinately larger.
This all flies in the face, of course, of Reynolds' assertions in that regard...most intruiging - or at least I thought so.
I'll be watching for any future stimulating discussion amongst those, who in many cases, are so much more senior and more learned than I can ever hope to be. M.S.

Patrick1 May 30, 2012 13:52

Quote:

Originally Posted by Mentor Sproxie (Post 363514)
.
I'll be watching for any future stimulating discussion amongst those, who in many cases, are so much more senior and more learned than I can ever hope to be. M.S.

The report that I read on the website is very poorly written, and has no structure or obvious aims so I couldn't understand much of what he was trying to say. But the gist is that laminar to turbulent transition is a myth in pipe flows, right? This is what I read: http://www.newdirectionforfluiddynam...20overview.pdf

The guy sounds like a typical conspiracy theorist to be honest. Like those people that come up with 'free energy devices' then say that the state won't let take them seriously because energy companies would loose money. He was talking about how the establishment won't accept his ideas and all that stuff...

I didn't get what he was saying about the Reynold's number being a false result or something, but I'm sure somebody else would have realised that out by now if it was true. He seems to be a typical crackpot, thinking that he alone has found something that goes against hundreds of years of scientific research by the world's finest minds, without even having a relevant qualification it seems. And of course, the establishment won't listen because they have a vested interest in the Reynolds number being true. What this vested interest is exactly I really do not know. As far as I know, nobody is making money out of the Reynold's number itself.

Anyway, if I have not misunderstood, please watch this video, which clearly shows the laminar to turbulent transition in pipe flow:

http://www.youtube.com/watch?v=KTEN5kwe9TM

Another one showing the Reynold's experiment and the transition:

http://www.youtube.com/watch?v=xFCXG...eature=related

cfdnewbie May 30, 2012 19:03

Can you spell 'hokum'? ;) don't let yourself get confused by stuff like this!

Mentor Sproxie May 30, 2012 21:31

only a challenge to a narrow definition of laminar-turbulent transition, I gather
 
Thanks for your responses,
I think this guy, however, does seem to at least have a question or two which any academic worth his salt should surely be able to address specifically, not merely with generalisations, for an open minded novice.
After all, those Uni. of Pennsylvania people do tend to concur as regards small vessel behaviour vs. larger ones, as well as in regard to a 'narrow' but allegedly important definition of the word 'transition'. They were unable to find that the Reynolds (presumably) definition of a 'transition' manifested/occured in a very similar context, seemingly.
That guy, the medical researcher, with an interest in blood flow like Poiseuille before him, had an open challenge out there, for many years to anyone who could tell him where Reynolds got his specific 'transition' data points from, which define: that PARTICULAR laminar-turbulent transition with its supposed inherent properties, as proposed by Reynolds and now, in my own immediate experience throwing me into confusion due to the two independent sources of 'questioning' I've been fortunate OR unfortunate enough to become privy to. They don't exist in the listing of observed data Reynolds claims to have used when graphing his results in his famous?..Diagram III (Royal Society 1883) in which the c-c line departs from a straight line in the top right hand corner in a scattered fashion, according to Tucker.
No-one ever gave this guy any satisfaction, with any sort of direct point-for-point discussion, or analysis, or serious attempt to refute things in any sort of scholarly way at all, I gather. Nor even was any attempt at an explanation as to where Reynolds got those extra plots from - he reckons it's the 'case of the missing data'.
I wish, in a way I'd never become privy to any of this - oh well! M.S.

Martin Hegedus May 30, 2012 23:56

What exactly is being discussed here?

I did a quick search on "The Transition from Laminar to Turbulent Flow in Liquid Filled Microtubes" got this http://www.ideals.illinois.edu/bitst...2/297/1030.pdf and this is stated in the conclusion

"The flow of a liquid in microchannels should be represented well by continuum theory unless the channel dimensions approach the slip length at the wall, estimated to occur for channels and tubes whose dimensions lay below a few microns. Despite this expectation, significant departures from continuum macroscale theory have been reported in the literature of microfluidics, and they have sometimes been attributed to unknown microscale effects that produce transition to turbulence at anomalously low Reynolds numbers. To resolve this controversy, experiments have been performed in round glass microtubes with diameters ranging from 50 to 247 microns, using liquids with different levels of polarity. The experiments consisted of accurate observation, in more than 1500 cases, of flow resistance measure by pressure drop and flow rate and velocity fluctuations measured by micro-PIV.

The results show conclusively that below a critical Reynolds number for transition to turbulence the flow is described, to within 1% experimental accuracy, by the classical macroscale result for Poiseuille, f = 64=ReD. More importantly, they show that the transition to turbulence first begins in virtually the same Reynolds number range as that found for macro-scale flow: ReD =1,800–2,300. Lastly, within the transition range, the behavior of the each microscale flow property — pressure drop, mean velocity and RMS velocity — is consistent with macroscale data. Thus, the behavior of the flow in microtubes, at least down to 50 micron diameter, shows no perceptible differences with macroscale flow. Once demonstrated, the applicability on the microscale of Osborne Reynolds’ simple criterion for transition to turbulence may not seem surprising. Evenso, one must be thankful and at least admit to some admiration for a criterion that continues to describe turbulence in, for example, water moving at speeds greater than 150 kph through a tube whose diameter is less than that of
a human hair."

Frankly, the results are not surprising. If the governing equations (mass, momentum, energy, equation of state, equation of viscosity) are the same, if the non-dimensional variables are the same (i.e. Reynolds number), if the geometry is similar, and if the boundary conditions are the same, the flow will behave the same. So if the macro-scale model exhibits transition, so will the micro-scale. And I hope that no one is saying laminar or turbulent flow does not exist at the macro-scale.

Mentor Sproxie May 31, 2012 04:05

thank you
 
Dear Martin Hegedus,
Thank you very much - I think I can now start to reconcile at least some of those loose ends, which had been bothering me.
A lack of general acceptance of the 'same behaviour' existing in tubes both large and small may, by the sound of it, have caused important research into atherosclerosis (particularly in the context of contamination by airborne toxins) to be shelved, years ago, for that medical researcher I mentioned.
The same guy, I notice had a paper published "Pulmonary Clearance [..from the airways..] of Inhaled Particles" (A.D Tucker) in the American Journal of Applied Physiology in 1973, which may have added a very important new dimension to the understanding of these things, especially where soluble contaminants (microparticulates etc) are concerned. I was reading about all of this via yet another source I can't readily recall, which also stated that at both Stanford and MIT, people like Professor Kline (Stanford University) welcomed him with open arms, when he visited them in 1983, hailing him as "the lung function man". Then everything, it's said, then turned sour for the reasons I've quoted. Oh well...
It all seems a great shame really! M.S.

Martin Hegedus May 31, 2012 10:24

Oh, the discussion is focused on blood. I thought it was a general comment. Blood is not a Newtonian fluid under all conditions due to the presence of red blood cells and, to a lesser degree, other stuff (fat, proteins, etc).

From Wiki (Blood viscosity)

"The fluid must reach a shear rate of about 100 (sec−1) to be assumed Newtonian. Until this point is reached the term viscosity cannot be applied to blood."

It's also, as far as I understand, more complicated then that.

Mentor Sproxie May 31, 2012 18:53

another helpful insight
 
Thanks again to Martin Hegedus.
Yes, that all makes every bit of sense, and only seems to help with the notion that it's NOT going to be the case: that you suddenly find yourself dealing with a reversal of pressure (which had been purported to be a phenomenon that would make small vessels, of that sort, behave differently from larger ones)...at the site of an arterial flow divider. For that matter nor would it be a valid reason for rejecting work done in the area of blood-flow physiology, which observed tissue fluid being drawn into the blood stream, through a known-to-exist tiny aperture at 'that' site. This is the best handle I can get on things at this stage, and for that I am certainly grateful.


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