Teardrop aerodynamics... in reverse! - Page 3 - Fuel Economy, Hypermiling, EcoModding News and Forum

winkosmosis · 03-09-2009, 03:57 PM

AFAIK, a pointy cigar is the optimal shape for a given volume with airflow parallel to the object. The only reason a rounded front is better is to be able to handle flow at an angle.

That's why the hulls of ships are cigar shaped with a pointy front and back.

hypermiler01 · 03-09-2009, 04:04 PM

winkosmosis · 03-09-2009, 04:22 PM

Here is something interesting.. The optimal shapes for holding pressure in a submarine are cylinders and hemispheres. But that is not the best for drag, so submarines used to be designed with an external hull that wasn't sealed, and it would be pointy on both ends.

submarine: Definition from Answers.com

MetroMPG · 03-09-2009, 05:04 PM

Quote:

Originally Posted by winkosmosis

That's why the hulls of ships are cigar shaped with a pointy front and back.

Ships (and some subs) need pointy bows for reasons other than drag. (Hint: think waves.)

Note that the part of a ship which works at the air/water boundary (ie. where there are waves) is generally pointy, but if it has a fully submerged drag reducing bulb, it is well, bulbous.

winkosmosis · 03-09-2009, 05:18 PM

The purpose of the bulb is to change the shape of the bow wave so it doesn't interfere with hydrodynamics at the rear of the ship. It's optimized for a particular speed

Bulbous Bow

MazdaMatt · 03-09-2009, 05:29 PM

You can't confuse hydrodynamics and aerodynamics. They work pretty differently. We're not trying to pull your leg here. Simply google "lowest cd shape" and you'll find a million references to an airfoil (aka teardrop). Dig deeper and you'll see why the bulb is better than a flat front or a pointy front. Better yet, search around this site. This dead horse has been beaten into a unrecognisable bloody spatter.

i_am_socket · 03-09-2009, 05:32 PM

I like to save this for special occasions:

hypermiler01 · 03-09-2009, 06:05 PM

The only way that I can see how a round front is "better" than a pointy front are the other non-aerodynamic reasons for having a short overhang.

Those pictures Piwoslaw posted very clearly show better airflow under the nose. The pink stream quickly reattaches, and stays attached the entire length of the underside, while the pink line under the semi round front is destroyed and never reforms.

I would also bet that barometers placed at the nose would show better, lower readings in front of a pointy nose.

I am also inclined not to think that the engineers of Porsche, Ferrari, McClaren, Mercedes, Audi, etc. are completely clueless.

hypermiler01 · 03-09-2009, 06:23 PM

And why do all the fast fish have pointy noses AND pointy tails?

hypermiler01 · 03-09-2009, 06:28 PM

I mean seriously, don't those noobs over at Aptera realize that their design would be more efficient with a hemispherical nose? LOL