Quote:
Originally Posted by aerohead
I agree with all the members who've already mentioned laminar boundary layer bodies.
The Delft team told me that this was the premise for their designs.
Keeping the max cross-section aft held the forebody in a favorable pressure gradient for laminar boundary layer (low skin friction),The turbulent boundary layer transition was held far back on the body,and so much kinetic energy was available in the TBL due to the forebody,that more aggressive curvature in the rear (reduced wetted area ) could maintain attached flow.
This is all predicated upon 'calm' conditions.Once the wind comes up,the body in immersed within Earth's turbulent boundary layer,and the ambient air turbulence kills the laminar boundary layer,especially in a crosswind which contaminates it,forcing an immediate TBL transition.
Keeping the envelope as small as possible (length) helps because it directly affects Reynolds number,of which LBL is directly related.
|
That's interesting. I used to think that Eivie was the best design out there, just limited by the riders (there were 2, Damjan Zabovnik, but also Francesco Russo had a bike like that built together with Damjan). Much closer to tear drop than Eta of VeloX as well as lower frontal area. There's a wheel far in the front which is not good though.
Still, I've seen people explaining its uniqueness by being too extreme for most riders. Sounded reasonable enough, I hadn't questioned it.
But according to what you report, the design may simply be inferior in low wind (which is probably the only state that matters when setting records).
Could you tell more about the Delft comments? Can you share your thoughts too?
Added:
On a related, but separate topic, have they talked about their gripes with CdA measurements in their wind tunnel?
I ask because on
their blog they say:
Quote:
|
Even though the values have dropped greatly in comparison to last wind tunnel test, we still have our doubts about them because we noticed a lot of fluctuation in the measurements. Therefore, the wind tunnel measurements do not seem to be very accurate.
|
I ask mainly because the current record holder for the lowest ground vehicle Cd is Ecorunner V from another Delft team. The said fluctuations make me have my reservations about whether Ecorunner V really has drag so low.