N12ck wrote:McMrocks wrote:
agree
Flow through a pipe is not smooth in the slightest, it is not laminar, and is very disturbed with the boundary layer getting bigger and bigger and more disturbed as the pipe goes on, without a pipe (tunnel) the flow would be much better,,,
unless, the pipe constricts the flow and forces it into a smaller exit volume to create higher pressure over the top of the diffuser along a concentrated jet of air (from the tunnel) -wild idea
This is rather general sentence and as such I tend to disagree, because it will depend on the conditions.
At low Reynolds numbers the flow is laminar. As the Reynolds number increases it becomes turbulent after going through a transition region, that said, we don't know the velocity of the air feeding that duct|tunnel (presumably from the lower sidepods stream, most of which derived from turning vanes and bargeboards), nor we know what's inside that duct, i.e. profiles.
I do not agree about the surface drag which someone has mentioned previously - since this is type of drag caused by skin friction, I don't see large disadvantage here - it's rather ducting the air vs. free stream.