Talk:Boundary layer thickness

Fluid type

The introduction to the article mentions air flowing over a flat plate. The remainder of the article should probably specify whether the approximations are valid only for air, or whether they apply to eg. any newtonian fluid.--JB Gnome (talk) 19:30, 20 November 2012 (UTC)

Parameters

Surely the parameters used in all the equations should be listed / explained.....

what is v? Kinematic viscosity?

192.249.47.196 (talk) 16:53, 17 November 2009 (UTC)

added some parameters —Preceding unsigned comment added by 96.229.173.44 (talk) 16:51, 2 May 2011 (UTC)

Error in Momentum Thickness?

Is the integrand for momentum thickness supposed to only contain momentum ratios? Compare equation (10.96) on page from ISBN:3540662707 from an an updated version of the cited Schlichting text. In that reference, the momentum thickness integrand contains only momentum ratios, not a velocity ratio. RhysU (talk) 17:43, 9 October 2013 (UTC)

However, for comparison, Smits and Dussauge give it as presented on their page 214. As do Liepman and Roshko on their page 324. Perhaps just a typo in Schlicting. Either way, getting a working reference from these IBSNs would be helpful. RhysU (talk) 17:55, 9 October 2013 (UTC)

To decide which of the two compressible momentum thickness equations is correct, it is best to look at how it is used. The one obvious choice is as part of the compressible momentum integral expression. In that context, the version currently in use appears to be correct according to the derived form in David Whitfield, "INTEGRAL SOLUTION OF COMPRESSIBLE TURBULENT BOUNDARY LAYERS USING IMPROVED VELOCITY PROFILES," AEDO-TR-78-42, 1979. — Preceding unsigned comment added by David Weyburne (talk • contribs) 11:11, 20 May 2020 (UTC)

Merging

I strongly agree that the separate pages for displacement and momentum thickness should be merged onto this page. It's silly to have them split up, and confusing to have duplicate pages. —Preceding unsigned comment added by 213.143.133.108 (talk) 13:35, 13 January 2011 (UTC)

New section : "Motivations for boundary layers"

Hello,

I am a relatively new contributor, and I suspect the section I just added is a bit of duplicate with the article boundary layers. However, I think a (hopefully) not-to-technical introduction is needed in this article before jmping on the details of calculations. Hence my edit.

Feel free to revert/modify if this violates any WP rule about duplicates. I just hope to prompt for some change if needed.Tigraan (talk) 23:47, 2 July 2013 (UTC)

Label(s) needed in the graphic to improve clarity

The dashed line in the graphic had me stumped for a while. It has no label and is not mentioned anywhere in the text of the wiki. I understood that within the boundary layer the flow had variable velocities, from zero at surface to the free flow rate at the edge of the boundary layer. But because I thought the graphic showed a plate of infinite extent, the dashed line made no sense to me.

Finally I figured it out: I noticed that the plate or surface is not infinite to the left and right... it has a leading edge towards the left. ...and it is from this leading edge that the dashed line emanates. Thus the dashed line defines the boundary layer - a constant thickness (i.e. height) far to the right, but a very variable thickness near the leading edge, shrinking to zero at the edge. Within this boundary the flow rates are variable, and outside (above) this boundary all the flow is free.

In this graphic, I recommend a label at least to identify the leading edge of the plate/surface, and ideally also a label to identify the boundary layer dashed line.

I'm a technical illustrator and would be glad to re-create this graphic with these improvements. How does one go about submitting an improved graphic to the wiki page?

thanks

Retroformat (talk) 18:24, 5 March 2018 (UTC)

Soole ratio?

Does anyone have a reference for the "Soole ratio"? A Google search came up empty. — Preceding unsigned comment added by David Weyburne (talk • contribs) 10:37, 19 May 2020 (UTC)

Changes being made

A number of changes are being made, some in response to the Talk section comments, and one major change dealing with exterior boundary layers. Anyone doing simulations of air flow over a wing section knows that the traditional boundary layer description does not work for this case. A new section is being added to deal with the peaking in near the boundary layer edge and the modified characterization parameters needed to describe this behavior. Additionally, the following changes in response to the Talk comments have been made: 1) "air" flow has been replaced by "fluid" flow in the introduction, 2) all parameters are now identified, 3) a reference to the correct compressible momentum thickness formula has been added, 4) descriptions have been added in the text to fully explain the Figures, 5) the Soole ratio has been dropped since no reference could be found, and 6) the Energy Thickness is demoted to a single sentence since this parameter is rarely used. David Weyburne (talk) 10:32, 27 June 2020 (UTC)

Examples

Any chance of some examples of actual thicknesses of the boundary layer in aviation from leading edge to transition point to turbulent flow eg 787 airliner, sailplane etc? JMcC (talk) 19:26, 14 March 2021 (UTC)