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Turbulent boundary layer

by Voidses_
Tags: boundary, layer, turbulent
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Voidses_
#1
Oct21-11, 03:33 AM
P: 10
Lets go straight to the point.

I need to find a way to calculate the displacement thickness of a turbulent boyndary layer. The laminar part has been simulated with Thwaite's method but I need to go from there. I'v heard of "Head's-model" but can't find the solution for it. Anyone that can point me in the correct direction or know of a better way?
I'll be using it in combination with a simple panelmethod-algorithm.

Thanks!
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boneh3ad
#2
Oct21-11, 07:57 AM
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Well for starters, how are you determining where the boundary layer is transitioning?
Voidses_
#3
Oct21-11, 12:40 PM
P: 10
Quote Quote by boneh3ad View Post
Well for starters, how are you determining where the boundary layer is transitioning?
I'm planning to use a semi empirical formula that puts Rex in relation to the shape factor. I't rather long so I won't write out all of it but it looks simple enough to use.
LHS is log(Rex) and RHS depends on the shapefactor alone. When LHS=RHS transition is predicted to occur.

boneh3ad
#4
Oct21-11, 01:01 PM
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Turbulent boundary layer

Is this on a flat plate? I don't know what formula you are using off the top of my head but in general there is no way to find [itex]Re_{tr}[/itex]. It won't compare too well with experiments.
Voidses_
#5
Oct21-11, 02:52 PM
P: 10
Quote Quote by boneh3ad View Post
Is this on a flat plate? I don't know what formula you are using off the top of my head but in general there is no way to find [itex]Re_{tr}[/itex]. It won't compare too well with experiments.
I appreciate the help!
I'v realised the problems involved in predicting transition from what I'v read. And no it's not a flat plate.
This particular equation can be found in Aerodynamics for Engineering Students. The book say the method was devised by Smith and H.Gamberoni at Douglas Aircrat Co. It's based on a more complex method of prediction that they found.
I don't expect to find the exact transition point and I'm not too concerned about that at the moment either. Finding the transition point is something that can be alterd later and knowing how innacurate the rest of the algorithm is... lets just say it doesnt matter too much. I just want something to start with and work from there when the basic structure of the algorithm is working.
boneh3ad
#6
Oct21-11, 05:13 PM
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Well at any rate, I can't really help you off the top of my head until I go back to work Monday. There are two sources that jump to mind that may have the information in there, which are "Boundary-Layer Theory" by Schlichting and "Turbulent Flows" by Pope. You may want to check there. I just don't remember off the top of my head because my work doesn't deal with turbulence and my copies of those books are at work.
Voidses_
#7
Oct22-11, 04:17 AM
P: 10
Great, Thank you!
I'll check with the campus library if they have them.


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