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Lack of pictures
An article like this would be greatly improved with some pictures, does anyone have any? I'll try and find some but I was thinking something along the lines of:
-Moody chart for a sphere, as the change in friction factor is well explained by boundary layers.
-Smoke blowing past a sphere or aerofoil in a wind tunnel.
-Transition to turbulence, flow over a flat plate perhaps.
-Velocity profiles (and temperature profiles) for flow over a hot plate.
-Flow through a duct showing the effect of adverse pressure gradients on boundary layer separation.
Anyone got any other suggestions? Andrew.Ainsworth23:32, 22 May 2007 (UTC)[reply]
Why is the turbulent profile so much higher than the laminar profile? I was always taught that both profiles had the same area of effect, but that the curve of the turbulent profile was a little different- the curve was "fuller". This does not seem to be reflected in the drawing. I'm not sure I like how they are set up one beside each other either. The two profiles should be separated more to avoid confusion.--Dj24500:02, 23 October 2007 (UTC)[reply]
I authored the picture so it might help if I try to explain it a little. I wanted to contrast the difference between the free stream, laminar and turbulent velocity profiles on the same picture - given that the notion of a boundary layer is tightly couple to velocity profiles. Next, I wanted to show there is a transition region between the turbulent and laminar regions, so I used a fade between the two colors representing the fully developed laminar (dark blue) and fully developed turbulent (red) regions. Finally I wanted to show that a turbulent boundary layer is thicker than the equivalent laminar boundary layer at the same location, hence the hump at the transition point. Of course the vertical scale in the picture is greatly exaggerated to highlight the height difference. However, turbulent boundary layers are thicker, causing higher drag, than an equivalent laminar boundary layer - assuming it could remain laminar. Syguy16:36, 23 October 2007 (UTC)[reply]
The speed profile of the turbulent flow does not represent the diffence between laminar and turbulent flow. It seems like it was just an upscaled-in-height laminar degree 2 v-profile, but its not. In turbulent flow, the velocity stays high much closer to the wall, with much higher gradient close to the wall, wich is the main reason for the higher drag. I´m sure you know. The exact thing is all but trivial, but there should be the possibility to notice the difference at first sight. Could this be changed?
Naval architecture
I moved most of this section to added mass, since it seems to confuse added mass with boundary layer effects. For instance for a ship of 100 m length and 10 m draft, at 20 m/s, the boundary layer will be of the order of 0.1 m thickness, so a boundary-layer mass of 2x100x10x0.1×103=200×103 kg. Which will be only a tiny fraction of the ship mass. The remarks about mass affected by aircraft are off-topic: not about naval architecture and not about boundary layers, so I removed them. -- Crowsnest (talk)
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