Calculation of boundary layer thickness
Calculation of boundary layer thickness
(OP)
Hello All,
I would like to know how to calculate the boundary layer thickness for a flow through pipes (internal flow). I can find a lot of information of boundary layer thickness for flow over flat plate, but not for internal flow. Any help is appreciated
Thanks
I would like to know how to calculate the boundary layer thickness for a flow through pipes (internal flow). I can find a lot of information of boundary layer thickness for flow over flat plate, but not for internal flow. Any help is appreciated
Thanks





RE: Calculation of boundary layer thickness
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RE: Calculation of boundary layer thickness
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RE: Calculation of boundary layer thickness
You're kidding, right? Even entry-level fluids texts talk about the "no-flow boundary" that exists between any flowing stream and a "surface" that is moving at a different velocity (i.e., the pipe wall with v=0, or the control surface on an airplane with a velocity many orders of magnitude greater than the air it is flying through). My graduate fluid mechanics text was titled "Boundary Layer Theory".
These boundary layers are very thin, a few million molecules thick, but they have a profound effect on fluid dynamics.
I have a feeling that the OP was asking a classroom question, so I'm not going to answer his question, but "fully developed flow" is a condition that happens between the boundary layers (if it happens at all).
David
RE: Calculation of boundary layer thickness
RE: Calculation of boundary layer thickness
No, not kidding. What castmetal said. Think of laminar flow development in a pipe - in fully developed flow, the velocity profile is a perfect parabola. The whole flow is affected by the "boundary layer". Same thing happens in turbulent flow, though the profiles are fuller. BL flow theory mostly grew up from Couette flow, one of the few fully-solvable Navier Stokes problems...
Boundary layers can be as thin as you say, but can also be dang thick (e.g. the boundary layer on the tail of a WW1 zeppelin, I think the bl momentum thickness (99%) is in meters there, but I didn't do the calc, just new a gal who had ;). Really depends on the local Reynold's number.