Talk:Law of the wall

Viscous sublayer

I disagree with the current description of the viscous sublayer. The viscous sublayer by its name refers to a boundary layer component where the viscous effects play the role. That means the viscous sublayer stretch from the wall ($y^{+}=0$) up to the log-law region ($y^{+}<30-50$). The viscous sublayer is then split into a laminar sublayer and buffer zone. The laminar sublayer ends at $y^{+}\approx 5$. Note that the buffer zone is a part of the viscous sublayer. The whole composition is nicely depicted in Cebeci and Cousteix, Fig. 6.3, page 166.

The error between both velocity profile functions, the linear and logarithmic, in the buffer zone is an effect of both viscous and Reynolds stress acting at once. The derivation of each law in its region ignores the stress component of the other. That is in the laminar sublayer the linear law is based on the assumption of viscous stress only. While in the log-law region the assumption about the wall shear stress contains only the Reynolds stress and neglects the viscous stress. Vita (talk) 10:28, 2 November 2017 (UTC)

Yes. The figure is wrong. The log-law should hit the y-axis around 5 not zero. 82.130.95.27 (talk) 14:59, 6 October 2022 (UTC)

References

Article name

The name "universal logarithmic wall law" is not the most common one. A search in Google Books for the following exact phrases gives:

• "universal logarithmic wall law": 4 hits
• "logarithmic law of the wall": 627 hits
• "log law of the wall": 163 hits
• "law of the wall": 905

Although the last one gives more hits, it is less descriptive than "logarithmic law of the wall". I therefore propose to rename the article consequently. -- Crowsnest (talk) 21:56, 17 March 2009 (UTC)

In geology, physical geography, and civil engineering (the 3 fields I can speak for), it's simply called the "Law of the Wall". So although this is less descriptive, perhaps it should be re-named? I'll also try to clean this up and actually add real equations sometime. Awickert (talk) 09:49, 27 March 2009 (UTC)

In the above Google Book search, these 905 hits with "law of the wall" must also include all 627 hits of "logarithmic law of the wall". But I am unable to exclude those directly in the search. One would guess that 905−627=278 hits solely contain "law of the wall".

But more fundamental is what experts in the field think of it. For instance Schlichting & Gersten (2000), p. 524, talk about the "logarithmic overlap layer" and call the term "logarithmic law of the wall" misleading. While laws of the wall u₊=f(y₊) do exist (near a smooth wall).

So I support your idea of a rename. It also makes it easier to expand the article with the power laws of Barenblatt et al, etc. -- Crowsnest (talk) 12:07, 27 March 2009 (UTC)

I added some formulas, but more can be done, e.g. y₀ for smooth and rough walls. -- Crowsnest (talk) 14:03, 27 March 2009 (UTC)

Huh - I've got to do some reading, it seems, as the only one with which I am familiar is the logarithmic one; it seems that that's also the only one that [CFD Wiki] knows. I'm guessing that this might be because I am more of an end-user of fluid flow equations than a developer. In any case, whether we just talk about the log one or generalize, I would support a move because of my Google results. On Google Scholar, there were 7110 for "law of the wall" vs. 1150 for "logarithmic law of the wall", making it without "logarithmic" win by a landslide, even after subtracting the overlap. A larger landslide exists on normal Google: 93,900,000 vs. 55,400. So for either reason (or both), I'm going to move it.

I've got some stuff on smooth and rough walls, and specific applications; I'll add that in soon-ish. Awickert (talk) 17:53, 27 March 2009 (UTC)

All right, I beefed it up to the extent of what I know. Awickert (talk) 22:41, 27 March 2009 (UTC)

Scaling By Viscous Scales

Do you think it is worth the time to create a separate article dealing with wall units, friction velocity, friction reynolds numbers, and the like (including momentum length scaling)? Mech Aaron (talk) 22:03, 29 July 2009 (UTC)

Yeah, maybe. Or maybe something more general, like "scaling in fluid dynamics"? I did make an article on shear velocity, which is synonymous with friction velocity. In any case, the wall units should probably be defined here unless you create something about them. Thanks a ton for the additions by the way. Awickert (talk) 04:48, 30 July 2009 (UTC)

Ok maybe something like "Length Scales in Wall Bounded Flows"? I really am not an expert, but just dealing with all of this in my masters right now, so it would be in "equation then explanation" format for right now, i.e. no applications. I will work on it when I am feeling unproductive in my research.Mech Aaron (talk) 19:22, 30 July 2009 (UTC)

That's the way to do it. I edit wiki a lot when my computer is chugging away at numerical models and data analysis. As for the article, would this all be for cases in which the main body of the flow was turbulent? If so, it could probably be stuck in here. Or it could be in a separate article which wouldn't be what people would search for, but which could be a very useful thing to link to. Anyway, I'm glad you want to add info, and I'm willing to help out with any of it so long as I know what I'm talking about. Awickert (talk) 23:30, 30 July 2009 (UTC)

Query

I have found the TBL diagram very useful in my current work, but it appears to differ from other similar diagrams I have seen in that the inner and outer regions do not overlap. Is it possible for someone to clarify this point for me? Thanks WaltLankor (talk) 20:43, 18 July 2012 (UTC) WaltLankor