Talk:Laminar flow

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Picture of a submarine The picture of the submarine shows not laminar flow as stated in the description of the picture. The flow is only laminar for the first few centimeter from the leading edge of the submarine, assuming a critical Reynoldsnumber of 10000, and normal viscosity of water.

It certainly appears to be laminar for several feet. Perhaps microturbulence does start earlier on, but only reaches a visible level when the bubbles appear in the water. StuRat 05:25, 14 June 2006 (UTC)

The flow arround the front of the sub shows very little deformation of the water surface, thus one might think that the flow is laminar, but at high Reynoldsnumbers like for flow arround a submarine, flow is always turbulent. Think of a river surface without wind, the watersurface appears flat, but the flow is actually turbulent. Also, the braking of the wave, causing the white spray has very little to do with the turbulence, as one might think from the description of the picture. The word microturbulence is misleading since the instability phenomenons causing turbulence are responsible firstly for the big scale turbulence, which is then transfered via mediumscale and microscale turbulence to the fluid viscosity. Gudo 14 June 2006 (UTC)

Inviscid flow

I am under the impression that inviscid flow is non-laminar. I think the point about inviscid flow should be changed to a point about creeping motion (Stokes flow) which is the exact opposite of inviscid flow - viscous effects are much greater than inertial effects. Any thoughts? Easyl 15:05, 12 January 2007 (UTC)

I will go ahead and make the change Easyl 11:43, 23 January 2007 (UTC)

Reynolds Number

This article says Laminar flow occurs when the Reynolds number is < 2040, but the Reynolds number article says Laminar flow occurs when Re < 2300. Which is correct? — Preceding unsigned comment added by Bungeh (talk • contribs) 03:24, 18 September 2012 (UTC)

The two are almost the same. Reynolds numbers shown on diagrams are usually shown on a logarithmic scale. The logarithm of 2040 is almost the same as the logarithm of 2300. Also, Reynolds number is used in numerous different applications - internal diameter of a pipe; distance along a pipe; chord of an airfoil; span of a wing etc.Dolphin (t) 22:44, 30 May 2015 (UTC)

Request photo

I appreciate the diagrams; however, I wonder if you can please provide a picture of what a laminar jet of water looks like also? 69.243.26.39 (talk) 20:27, 26 December 2012 (UTC)

Article lacks history section

This article would benefit from a history section to describe the chronological development of our understanding of laminar flow and the people responsible. FreeFlow99 (talk) 12:12, 31 December 2012 (UTC)

More than just velocity

the article made it sound like laminar/turbulent flow depended only on velocity but according to this it also depends on viscocity:

http://www.mit.edu/course/1/1.061/OldFiles/www/dream/SEVEN/SEVENTHEORY.PDF — Preceding unsigned comment added by 45.49.18.32 (talk) 06:33, 29 May 2015 (UTC)

Whether the flow in a flow field will be laminar or turbulent can be anticipated with some reliability by taking account of the Reynolds number. The Reynolds number is based on a representative speed, a characteristic length and the kinematic viscosity of the fluid. Alternatively, if the Reynolds number is based on the dynamic viscosity of the fluid, then the density of the fluid is also significant. Dolphin (t) 01:45, 30 May 2015 (UTC)

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high momentum diffusion low convection?

is this statement from the intro true? — Preceding unsigned comment added by 91.138.13.86 (talk) 17:46, 24 August 2018 (UTC)

Definition of laminar flow and citation

The first sentence, defining laminar flow as one with "parallel flow" is attributed to Bachelor, but looking through his book, I cannot find this stated anywhere. Does anyone have a page or section number to match this, as neither 'laminar' nor 'turbulent' appear in the index or contents? Section 4.2, where he discusses some laminar flows, seems to explicitly limit itself to flows which are both laminar and parallel (because those flows are linear, and therefore have closed-form solutions, which are interesting to Bachelor as a mathematician). This doesn't seem to me to define laminar flows as parallel flows, but rather just seems to be a limiting the scope of the work? Pope, similarly, appears to introduce laminar flows by example, in his case Reynolds' pipe flow experiment. This, too, doesn't appear to be a rigorous definition, but rather his example happens to be parallel, and the reader is not told explicitly if this is a general statement or not. Unfortunately, it also seems like a more rigorous definition that does not rely on specific flow topology (eg: through energy dissipation) might not help introduce such a seemingly basic concept, so I cannot offer a resolution at the moment. — Preceding unsigned comment added by 129.128.60.90 (talk) 23:12, 2 May 2019 (UTC)

I don't have access to a copy of Batchelor's Introduction to Fluid Mechanics (2000), but I do have his An Introduction to Fluid Dynamics (1967), Cambridge University Press. (When I do a search for "Batchelor Fluid Mechanics" I only find An Introduction to Fluid Dynamics. I wonder if the 2000 title Fluid Mechanics might be nothing more than the same book with a slightly different title for the North American market. Alternatively, he was the founder and long-time editor of the Journal of Fluid Mechanics; perhaps some confusion arose for that reason - the citation gives no information about the publisher of Fluid Mechanics.)

In An Introduction to Fluid Dynamics there is little or no information about the differences between laminar and turbulent flows; it's not that sort of book, being mostly concerned with the applied math of fluid dynamics, rather than the practical science. (In my book, Section 4.2 is titled "Steady unidirectional flow". Are we looking at the same title for 4.2?)

I take your point that Batchelor is not a good source for the information in the first sentence of our article. A better source that I have on my bookshelf is the 4th edition of Victor L. Streeter's Fluid Mechanics (1951 - 1966), McGraw-Hill. In Section 3.3, Streeter says "In laminar flow, fluid particles move along smooth paths in laminas, or layers, with one layer gliding smoothly over an adjacent layer. Laminar flow is governed by Newton's law of viscosity, which relates shear stress to rate of angular deformation. In laminar flow, the action of viscosity damps out turbulent tendencies." I will change the citation from Batchelor to Streeter. Dolphin (t) 02:27, 3 May 2019 (UTC)

I made this change. Dolphin (t) 02:42, 3 May 2019 (UTC)

My comment was a step further: it isn't that Bachelor was a bad source for the information in the first sentence, but I'm not sure that the first sentence is even correct. I am not convinced by the 'in layers' definition, since it's fairly trivial to set up a flow with a saddle point in the Stokes regime, which I think most people would agree is laminar. Similarly, I believe all flows are 'smooth' in the continuity sense (though the mathematical sense remains unproven) - even potential flows with explicit singularities in the flow. Is it too advanced to say laminar flows are ones where viscosity is important across all length scales, or too trivial to say laminar flows are not turbulent (though I think those definitions are equivalent)?