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In turbulent flow the friction is inertial for the most part: the chaotic flow causes the fluid in the faster moving center to interchange randomly with the fluid near the edge. This eventually allows momentum from the center to be transferred to the walls of the pipe (i.e. friction).

If the pipe walls had "rifling" (an internal swirling pattern), the fluid would rotate on it's way down. Rotation inhibits momentum exchange between the center and edges because of the Coriolis effect: a parcel of fluid moving outward will find itself moving inward at half a rotation later.

Could rifling reduce friction this way, or would the extra friction from the increased surface area offset any gains? Is there a way to intuitively see which effect will "win"?

Edit: CuriousOne pointed out a study that shows rifling seems to help: From "Experimental Study on Heat Transfer and Fluid Flow in Vertical Rifled":

"The pressure drop and the energy consumed by using the rifled tube were also found to be less than that of the smooth tube."

I don't know if this is due to the rotation or because the rifles act as riblets. This study is for only a single rifled tube, so there is still room for optimization.

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  • $\begingroup$ See something like A. M. M. Ibrahim, B. R. Elhub, H. A. A. Wahab, "Experimental Study on Heat Transfer and Fluid Flow in Vertical Rifled", Advanced Materials Research, Vol. 505, pp. 524-533, Apr. 2012? Experimentally rifling seems to have advantages, at least in some regimes. $\endgroup$
    – CuriousOne
    Dec 21, 2015 at 0:39
  • $\begingroup$ It seems if it were notably advantageous then we'd see it at least somewhere in biological systems (circulation, etc.) and I'm not aware of any instance. $\endgroup$
    – Digiproc
    Dec 21, 2015 at 1:08
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    $\begingroup$ @Digiproc: Evolution is driven by multiple concerns. In case of the circulatory system fat deposits and the formation of blood clots on uneven arterial surfaces is of known medical relevance (both are actually life threatening events), so it may be that the slight potential advantages are greatly suppressed by disadvantages. Having said that, I wouldn't be surprised if a knowledgable biologist may actually be able to give biological examples, so maybe one should post a similar question on the biology sister site? $\endgroup$
    – CuriousOne
    Dec 21, 2015 at 1:16
  • $\begingroup$ @CuriousOne: I think this is for two phase boiling water flow for which the liquid phase gets centrifuged out to the sides of the pipe and improves heat transfer. $\endgroup$
    – Kevin Kostlan
    Dec 21, 2015 at 1:22
  • $\begingroup$ I only have the abstract, which doesn't speak, at all, about boiling water. The temperature range seems to be 25-33 degrees C. Am I missing something? Having said that... I take no responsibility for the quality of the paper, just pointing out that people have done research and that you will find experimental results when you do a literature search. $\endgroup$
    – CuriousOne
    Dec 21, 2015 at 1:39

2 Answers 2

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One does not need to have rifling in a cylinder to induce rifled rotation of turbulent water flow; rifling is imposed on the fluid column by transverse echoing reverberation of flow-generated sound with an imposed resonant wavelength of twice the diameter (Google "Rifled Rotation in Turbulent Cylinder Flow (20/11/13"). The rotation might be explained by Sir John Tyndall's 1867 observation that specific simple harmonic sounds trigger turbulence in a flat flame that was previously laminar. The flame remained rotated until the triggering sound ceased.

Furthermore, in turbulence in cylinders a distinct organized flow pattern develops in equal cylinder sectors – a centripetal streaming flow flanked by equal, but counter-rotating vortices. Significantly, a central streaming flow flanked by a pair of entrained counter-rotating vortices is characteristic of flow away from a simple harmonic sound generator (Gaines, 1932, Physics, 3: 209-229.) or from a simple harmonic ultrasound generator (Liebermann,1949, Phys. Rev. 75: 1415-1422). This conforms to simple harmonic resonant transverse sound that develops as turbulence onsets in cylinders.

Significantly, in Nikuradse's study of turbulence in tubes with geometric cross-sections (such as square or triangular),his illustrations show a similar distnct transverse flow pattern – a centripetal streaming flow from the boundary layer of each mid-wall, flanked by a pair of counter-rotating vortices (Nikuradse J , 1930). Although rifling develops in turbulence in cylinders (a cylindical turbulent column in a similar cylindrical tube), a triangular-shaped turbulent column in Nikuradse's tubes cannot achieve rifling (one can't rotate a tiangula , 1932, Physics, 3, 209-229. r peg in a similar-shaped tube).

Such organized flow patterns contradict a astate of chaos.

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According to the Wikipedia article you referenced in your comment, the advantage of rifling in a boiler tube is that it creates centrifugal force which throws the heavier water phase toward the walls of the tube, keeping the lighter steam phase in the center. This allows better heat transfer from the walls to the water. Similar studies address the effect of limiting the size of steam bubbles forming on the inner wall by creating enough centrifugal force acting on the water to displace the steam bubbles toward the center before they get too large.

I'm assuming your question regards fluid flow velocity, and specifically the effect of friction between the inner wall of the tube and the fluid it carries. I don't think that Wikipedia article is helpful. However, you may be able to compare fluid flow velocity in each type of tube by using the Reynolds number for the particular fluid. Scroll down to "Flow in Pipe" in the Reynolds number link. In order to make the two types of tube comparable, and to isolate the coriolis effect, it seems to me you would need to adjust the dimensions of the rifled tube so that its cross sectional area (including the effect of the rifling which increases the wetted perimeter) equals the cross sectional area of the smooth tube.

You then could perform an experiment that measures the rate at which the fluid exits each type of tube. If the rifled tube produces a greater exit velocity, you might attribute this to the coriolis effect.

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