Is this flow turbulent or laminar?

[teoman]

Hello,

is it a case of turbulent flow over a wing if the relevant Reynoldsnumbers are 350.000 to 1.500.000?

Teoman

 

[Andy Resnick]

The onset of turbulence typically occurs for Re > 4000:

http://en.wikipedia.org/wiki/Turbulence

 

[teoman]

Isn't Re > 4.000 = turbulent only applicable to pipe flow?

Hello,

I thought Re > 4.000 = turbulent is only applicable to pipe flow?

Am I wrong?

Teoman

 

[random54]

It's turbulent for any Re > 4000. The calculation of Re number depends on what type of flow it is. For open systems (such the wing is in this case) you have to use hydraulic radius instead of charasterictic length used in pipe flows.

There is a wikipedia article how to calculate certain flows hydraulic radius:
http://en.wikipedia.org/wiki/Hydraulic_radius#Hydraulic_radius

 

[cjl]

It's turbulent for any Re > 4000. The calculation of Re number depends on what type of flow it is. For open systems (such the wing is in this case) you have to use hydraulic radius instead of charasterictic length used in pipe flows.

There is a wikipedia article how to calculate certain flows hydraulic radius:
http://en.wikipedia.org/wiki/Hydraulic_radius#Hydraulic_radius

Not really. Hydraulic radius is for channel flow. For external (non-channel) flow, it's true that Re = 4000 is not necessarily the critical reynolds number. Unfortunately, it can be difficult to get the true critical reynolds number without experimentally testing it, but it can be anywhere from a couple thousand up to roughly 1 million. In general, for a wing at Re = 3.5*10⁵ to 1.5*10⁶, I would guess that the flow is turbulent, as it is near the upper end of this range. At the very upper end of this range (Re just under 10⁶), you would probably only get laminar flow on a very smooth plate. Of course, just because turbulent flow exists doesn't mean that it's turbulent over the whole wing. If the wing surface is rough at all, you'd probably get a transition to turbulent flow pretty early on, but if the wing is smooth, a significant portion of the wing would have laminar flow. Again, I'm not sure how to determine exactly how much would be laminar aside from experimentally.