Teardrop aerodynamics... in reverse! - Page 2 - Fuel Economy, Hypermiling, EcoModding News and Forum

Memorytwo · 02-25-2009, 07:19 AM

2003 Civic SI

Piwoslaw · 03-09-2009, 05:15 AM

I threw a teardrop into Flow Illustrator, going both forward and backward, with parameters Re=8000000 and dt=0.023.

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hummingbird · 03-09-2009, 12:19 PM

I think the ideal shape is neither the forward teardrop nor the reverse one. The objective here is to avoid a detached flow- the forward teardrop pushes a sizable wall of air, the reverse one allows turbulence to form at the end face, increasing drag.

The Ideal shape would be a combined teardrop with the front end formed by a reverse teardrop tail and the back end formed by a normal teardrop tail. The intermediate section can be tubular shape that then reaps benefit of a parting already taken place - something like the bullet trains of Shinkansen Japan or TGV France.

MazdaMatt · 03-09-2009, 01:02 PM

I'm pretty sure, dispite intuition, that for a given vehicle length and height, the teardrop gives the best cd.

NeilBlanchard · 03-09-2009, 01:10 PM

Hi,

Here's the lowest Cd for a 4 wheeled vehicle:

The Schlor Pillbug (1937) has a Cd of 0.13. Food for thought!

MazdaMatt · 03-09-2009, 01:14 PM

That's a sweet ride

Any of your aero folks want to punch that drag co-eff and a "standard" modern RR and weight into a hp calculator? I'd love to know how powerful of an electric motor that thing would require at 60mph.

winkosmosis · 03-09-2009, 01:23 PM

A teardrop is the optimal shape.... for a teardrop. In reality, a car has different constraints than a drop of water. And a flat nose is NOT the same as a rounded blunt nose, so please stop saying all these cars would be more aerodynamic in reverse.

hypermiler01 · 03-09-2009, 02:26 PM

Quote:

Originally Posted by Piwoslaw

I threw a teardrop into Flow Illustrator, going both forward and backward, with parameters Re=8000000 and dt=0.023.

You can see that the pointy nose forward gives much better flow underneath the object, where it quickly attaches again. It will also have less pressure in front.

You can also see that having reduced slope behind is better for keeping the flow attached. Which leads to believe that the teardrop is NOT the ideal shape. Maybe something like this would be better:

MazdaMatt · 03-09-2009, 02:44 PM

Someone put that shape through flow illustrator, but use the same height and length as the teardrop.

hummingbird · 03-09-2009, 02:50 PM

hypermiler01 post 18 -- You're in my camp!