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Too much flow => large boundary layer

RisingSun

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Joined
18 May 2015
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36
I read a post by ceg that says too high of a flow can actually increase the boundary layer https://www.ukaps.org/forum/threads/flow-rates.32752/#post-348211.

"As fluids are put in motion their static pressure decreases and the Boundary Layer thickness becomes thinner up to a certain speed. Above that speed, the Boundary Layer again thickens up. So there is a small range of fluid velocities near the leaf surface where increased flow reduces the thickness of the Boundary Layer and facilitates transport of nutrients/CO2 to the leaf. At velocities below this range the thickness and pressures are high, and above the range the thickness and pressures also increase."

Does anyone know why this happens? Most sources I've read claim an inverse proportion where more flow = less boundary layer.
 
One possible explanation is that the laminar and turbulent flow have different boundary layer profiles. What could happen is that the layer thickness reaches a local minimum when the flow changes from laminar to turbulent, when a certain flow velocity is reached.
 
high flow over a surface creates pressure, which slows the flow. The theory is that above a certain velocity there is so much pressure the boundary layer effectively becomes trapped. but I doubt that happens in real life because the plant will give way and sway then flap around by all the pressure. IMO this is what makes it hard to photosynthesize. not the boundary layer, because if that were true plants wouldn't be able to grow in stagnant or low flow environments. This is because gases also exchange through osmosis.
 
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