100% Bluff Body Drag Reduction Theory

[Christ]

The main point of my post was that neither truck had had any treatment. In OE form, the "conventional" truck has more skin friction and shape associated drag, because the flow has to change direction so many more times.

[Frank Lee]

neither truck has a pre splitter on a jousting probe in front of it

[Christ]

Originally Posted by Frank Lee

neither truck has a pre splitter on a jousting probe in front of it

Word.

Back on Topic, the original post reminds me of a techology that was researched that is referred to as "Super Cavitation". Please google that term for more information.

[Frank Lee]

I believe we've "probed" this topic before here?

[aerohead]

I think the images are in 2-dimensional flow,so they'd be a little desceptive for 3-D.
A fellow at Bonneville in 1990 was attempting such a thing by attaching a sphere-on-a-stick ahead of a streamliner,and then attempting to draft behind it's wake.
I was given to understand that the fellow had just received a graduate degree in aeronautical engineering from Cal-Tech,or somewhere like it,and that this "technology" had been the basis for his Master's Thesis.
I was running my own car and didn't have time to visit with the fellow.It would have been interesting to hear about it all.
As far as I know,he did not set a LSR with the setup.

[Rokeby]

Originally Posted by Christ

...the original post reminds me of a techology that was researched that is
referred to as "Super Cavitation"...

This supercavitation phenomena is very interesting. For the most part, it is
associated with super high speed underwater objects; submarines,
torpedoes, and even bullets. It has to do with creating a gas bubble around
the object. It would appear that in water at least, speeds ~180kph, ~110
mph, are required.

SUBMARINE HEROES

I have found indications that the phenomena can also be created in air. I
haven't yet found what speeds are necessary to create/sustain
supercavitation in air. But, from the cavitators pictured below on
aircraft/missles, it would be well above typical highway speeds:

"Different nose geometries can be used to create supercavities flat discs,
cones, 'gear shaped' plates and cones (top and middle), faceted concavities
and cavitators with inscribed cones that move in and out like the tips of
ballpoint pens (bottom)."



It is noteworthy that the pictured cavitators are much closer to the main
body that the 1.5 x the main body's width given in the original architecture
derived arrangement. It may also be significant that the main bodies are
long, thin, and aerodynamically clean, not a "bluff body" like a car.

This from a very short preview article in Scientific American.
Access to the whole article requires a subscription or on-line purchase:

How to Build a Supercavitating Weapon: Scientific American

Wouldn't it be a surprise to be able to create the supercavitation phenomena
with an simple plexiglas plate, sort like an external grill block cum bug
deflector, located 6 or 8 inches in front of the grill, mounted to the front
bumper? I suppose the effect wold be to place a single whole-vehicle vortex
generator in front of the car to pre-energize the boundary layer.

Help! Somebody stop me! I'm saying things I know next to nothing about!

This quote isn't particularly encouraging:

"But super-cavitation technology might also be applied to aircraft, giving them brief stints of hypersonic speed when required, either for orbital insertion or escape from nearby threats. Note that SC transport requires a shape much like that of a rocket. "

And there is always this:

Originally Posted by Frank Lee

I believe we've "probed" this topic before here?

http://ecomodder.com/forum/showthrea...tion-9591.html


More research needed...

[silverinsight2]

Aero spikes have been around awhile

[thatguitarguy]

The pictures in the first posting don't show what the speed factor is. I don't think that the speeds we travel is anything close to what is needed for true cavitation, but a shape that would create some kind of vortex generation is more feasible, using the same principle.

How about this. Instead of thinking about a whole vehicle generator, start small and create a probe that would stick out in front of your mirror to generate a vortex to lessen the drag on the mirror. This would be easier to tuft test, and wouldn't get as much potentially undesirable attention as a clown nose on a pole in front of your car. And the smaller size would allow you to experiment more with the effects of different shapes shapes and sizes.

[aerohead]

Correct me if I'm mistaken,but while cavitation and supercavitation are certainly phenomena which operate within the study of fluid dynamics,for our purposes,they are limited to "liquids" not vapor or gases.
The low pressure around the structure allows momentary phase change to a vapor ( cavitation ) which,after passage of the structure attains a pressure regain at which ambient surrounding temperature allows for dew point condensation back to a liquid form,collapsing the bubble.
In the air,as an aircraft accelerates through stages of Mach you will observe condensation clouds of water vapor created as the local compressive heat of compression is released and visible droplets form in the colder low pressure of the rarefaction behind the supersonic shockwave.
For cavitation of the air to occur,the gases which form the atmosphere would have to be destroyed into free radicals and free atoms.Yes?

[thatguitarguy]

Beam me up Scotty...