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Thread: turbulent flow vs. laminar

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    RBW Member MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV's Avatar
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    turbulent flow vs. laminar

    I just came across an article on "Essouflement" in the german dive mag "Taucher", where CMM claimed that heavy breathing would result in turbulence in the upper airways, namely trachea, and that the soft lined upper airways would collapse from this turbulence, leadingamong else, to CO2 buildup.
    While latter clearly seems consequent to Bernouilly's Continuity Equation, and not to turbulence, would someone pls. do the math, which peak air flow in a trachea of a typical crossection of 19 mm diameter would occur, and at which gas density/ambient pressure the above claim would hold water?

    greets from somewhere between here and Egypt ( mindwise, got the late packing disease)

    Matthias

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    RBW Member richc is an unknown quantity at this point richc's Avatar
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    Re: turbulent flow vs. laminar

    Been a few years since I did any fluid dynamic modelling so I thought it would be fun to see what I thought.

    I think Re is 4000 (i.e. turbulent flow) at about 3 m/s peak flow. And stops being laminar (i.e transitional) at around 1.7m/s

    Although with some assumptions, and that's using dry air at 1 bar, 293 Kelvin.

    Any other offers?

    Rich

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    RBW Member abc is an unknown quantity at this point abc's Avatar
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    Re: turbulent flow vs. laminar

    Quote Originally Posted by MatV  View Original Post
    I just came across an article on "Essouflement" in the german dive mag "Taucher", where CMM claimed that heavy breathing would result in turbulence in the upper airways, namely trachea, and that the soft lined upper airways would collapse from this turbulence, leadingamong else, to CO2 buildup.
    While latter clearly seems consequent to Bernouilly's Continuity Equation, and not to turbulence, would someone pls. do the math, which peak air flow in a trachea of a typical crossection of 19 mm diameter would occur, and at which gas density/ambient pressure the above claim would hold water?

    greets from somewhere between here and Egypt ( mindwise, got the late packing disease)

    Matthias
    Quote Originally Posted by richc  View Original Post
    Been a few years since I did any fluid dynamic modelling so I thought it would be fun to see what I thought.

    I think Re is 4000 (i.e. turbulent flow) at about 3 m/s peak flow. And stops being laminar (i.e transitional) at around 1.7m/s

    Although with some assumptions, and that's using dry air at 1 bar, 293 Kelvin.

    Any other offers?

    Rich
    Reynolds number is (density x velocity x diameter)/ dynamic viscosity.

    If this number is greater than 2000 it is nearly always turbulent flow, much less than this, laminar flow.

    Note the density term is depth dependant so flow characteristics may well change as the depth changes.

    If dynamic viscosity is 1.82 x 10exp-6, density at 40m is say 5 kg m-3, and D = 0.019, and we assume 15 breaths per minute at 3 litres per in/out cycle, then U is about 5 m s-1 so Re is over 200000 so pretty sure to be turbulent.

    Corrections gratefully received !

    abc

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    RBW Member MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV's Avatar
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    Re: turbulent flow vs. laminar

    Hi Rich,
    Quote Originally Posted by richc  View Original Post
    I think Re is 4000 (i.e. turbulent flow) at about 3 m/s peak flow. And stops being laminar (i.e transitional) at around 1.7m/s

    Although with some assumptions, and that's using dry air at 1 bar, 293 Kelvin.

    Any other offers?

    Rich
    That is at 300 cm/s* pi*1,9^2/4*60/1000= 51 l/min SAC;,
    at 170 cm/s 29 l/min SAC.

    How does this compare with actually measured SAC?

    One should expect that at the moment turbulence sets in, breathing gas parameters should change significantly, like ventilatory quotient, exchange ratio, fraction of expired oxygen, CO2 buildup.

    From what I have read here (Navy diver reporting respiratory evaluation during exercise, similar studies with another Navy) own experience, SAC can go up to 130 l/min. At the surface. I believe there is data somewhere showing submerged SACs to be much lower.

    When I was once working hard at -33 m, I had an SAC of 60 l/min, and needed some time to catch my breath. no problem with gas delivery, though.
    In a competition, mono-finning like mad at the 100m distance, my overall AC was 130 l/min, at 1,4m depth. Breathing was hard from at the legs last 25 m.

    Btw, the focus of the article was that "Essoufflement" should be caused by turbulences hardening the breathing, which statement is subject to a quite controversial discussion, since most, including me, seek evidence that it comes from inadequate breathing for "psychological" reason, going from a neutral balance to one that shifts towards deficient expiration, leading to CO2 buildup and subsequent panic..

    Cheers,
    Matthias

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    RBW Member richc is an unknown quantity at this point richc's Avatar
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    Re: turbulent flow vs. laminar

    Quote Originally Posted by abc  View Original Post
    Reynolds number is (density x velocity x diameter)/ dynamic viscosity.

    If this number is greater than 2000 it is nearly always turbulent flow, much less than this, laminar flow.

    Note the density term is depth dependant so flow characteristics may well change as the depth changes.

    Corrections gratefully received !

    abc
    That's the problem with turbulence - what Reynolds number you take depends on who you ask. Lower than 2000 is pretty much universally laminar. Over 4000 turbulent. Some people try and get around it with 'transient' for the flows in between but actually defining turbulence as such is open for debate.

    Density will change with depth but I'd also argue so will viscosity with the gas you're breathing being compressible. Added to that the fact that it's probably not air you're breathing and certainly not dry air then the assumptions you make to get from the Navier-Stokes equations (such as assuming it's a Newtonian fluid) down to an easy calc for the Reynold's number becomes more and more tenuous. But resolving multi-dimensional N-S equations seems like awfully hard work when a ballpark figure will do. Which is why I gave a number for dry air at one bar....

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    Re: turbulent flow vs. laminar

    Quote Originally Posted by MatV  View Original Post
    That is at 300 cm/s* pi*1,9^2/4*60/1000= 51 l/min SAC;,at 170 cm/s 29 l/min SAC.



    From what I have read here (Navy diver reporting respiratory evaluation during exercise, similar studies with another Navy) own experience, SAC can go up to 130 l/min. At the surface. I believe there is data somewhere showing submerged SACs to be much lower.



    When I was once working hard at -33 m, I had an SAC of 60 l/min, and needed some time to catch my breath. no problem with gas delivery, though.
    In a competition, mono-finning like mad at the 100m distance, my overall AC was 130 l/min, at 1,4m depth. Breathing was hard from at the legs last 25 m.
    Those SAC's are very high, the highest I have had is 22 [4C water, stressful dive, working hard] and the lowest 10.2. My OC average was about 12-14, a bit higher now that I have lost some fitness.

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