List of aero mods you can do to your vehicle

[aerohead]

Originally Posted by radioranger

I read somewhere a while back where the Russians had developed a super high speed sub that shredded the water in front of it self to fly through the cavitized layer, anybody hear of that one , supposedly went supersonic. In the aircraft world just read where somebody put a prop spinner from a constellation on a DC 3 or similar plane and picked up a good bit of speed and much better engine cooling, whats going on there i wonder, whole nother world of course put eventually all these things tie in together,

I've read of a rocket-powered, super-cavitating, VA-111 Shkval torpedo, which operated beyond 230- mph underwater. Some of the rocket exhaust was shunted through the torpedo, and released at the nose, allowing the torpedo's surface to interface against a gaseous fluid, instead a liquid fluid. We wouldn't be able to utilize this phase differential on an automobile, as the atmosphere is always in gaseous phase.

[aerohead]

Originally Posted by bnmorgan

http://www.scribd.com/doc/40528006/Full-Text

An expanding cone would signify supersonic, shockwave drag/ ballistic airflow which would not be present even marginally on an automobile below 250-mph.
In the sub-sonic automotive flow, the sphere would begin with a maximum separation- induced wake of laminar boundary layer, then as critical Reynolds number is achieved, transition to its minimum wake of turbulent boundary layer.
In order for the car to hide behind the wake of the sphere, the sphere would necessarily have to have a larger frontal area than the car.

[aerohead]

Originally Posted by radioranger

Gotta point there, I guess another way is to duct air from a high pressure area to a lower one, sort of how they cooled the engines in the Shelby Daytona Coupes, cant think of any ordinary cars that do that , probably because of weather issues, I was also wondering if anyone has tried to relocate their mirrors to the door so the air can flow around the windsheild better, maybe sit the mirror out of the main air flow, maybe back a bit , and while ii am thinking about it has anyone ever tried the flaps in front of the rear wheels like SAAB cars used to have,

1) Ducting high pressure air to a location of low pressure does nothing to mitigate the flow separation responsible for the low pressure to begin with.
2) Air passing through the duct experiences higher skin friction losses than if it were to simply pass 'over' the body, losing valuable kinetic energy to irreversible heating.
3) Air robbed from the front of the car is not available to protect the boundary layer, which itself raises the probability of even worse flow separation, aggravating the pressure drag of flow separation.
4) 'Streamlined' vehicles typically have the least 'porosity' or 'ventilation' of any vehicles.
5) Streamline the vehicle and you'll kill off that low pressure.

[aerohead]

Originally Posted by RedDevil

It is even more subtle than that. In fact both the high pressure and the air-water interface have a function here.

When a boat moves through the water it needs to put aside the same amount of of water that it displaces. A 10.000 ton ship has to move 10.000 tons of water aside.
It requires a lot of force to set that amount of water in motion. That force is pressure; it needs to be higher than its surroundings. Once the water is moving aside its momentum will cause it to make way for the steadily increasing cross section area of the ship's bow.
When the bow finally reaches full width and the sides bend straight the water is forced to stop moving aside, creating low pressure. You can see that for yourself on any ship in motion; at the point where the hull straightens the water level will be slightly below the water line.

The protruding bulb forces itself through the water. As the water around it is not yet moving aside the pressure rises sharply, which accelerates the mass of water flowing aside and up.
But what goes up must come down. While the water that moves aside keeps doing that, the water on top recedes and transfers into sideways motion. Just at the point where it becomes level again the sharp edge of the bow cuts in. As the water is already moving down and aside it meets less resistance than it would have without the bulb.

The bulb serves in making the transition from a body of water in rest to that same body moving sideways more gentle. There is a close relationship between the rate at which the cross section area of a body moving through water varies and the resistance it meets. As you see the variation of the cross section as a function, you need to keep the second order derivato of that function as close to zero as possible.

You cannot fully apply aquadynamic rules to aerodynamics. But the base principle that when you move something through the air, the momentum of the displaced air does influence resistance and you have to keep its transitions gradual, holds true.
The first fighter jets that were able to break the barrier of sound could only just do that, and not for long due to massive fuel consumption. The breaktrough tor really fast jets came with the realization that the wings of the planes displaced air, and at supersonic speeds that air had nowhere to go. This was solved by narrowing down the fuselage by a comparable amount; the so-called Coke contour. (other solutions were swept wings and the Delta wing, which made the wings themselves displace air gradually).

In car terms, this means that you can compensate for anything you move into a stream by making a dent in another part close by so the total area does not change much, and the momentum of the air at some distance to the car is not disturbed.
Or you can gradually build up and recede the area just before and after the intruding bit for the same effect; like the leading and trailing spoilers at the wheels of low Cd concept cars. They work because of this principle.

Phew!
Anyway, a ships bulb bow would not work on a car; there's no water to lift and fall back. That said, it is the very mod I'm planning to do to my car.
I will replace my lower grill block by a bulge that slightly protrudes the front bumper and license plate of my 2011 Insight. It should curve back towards the sides to make a flush transition with the 45 degree angle of the front bumpers edges. But will not really stick out like a ships bow.
Before I do so I wil do some other simple mods and get some data on the MPG that yields as a base for further testing. Hope I can give some results soon.

Technically, it should make no difference. According to the literature, it requires very little leading edge radii on an automobile to fully 'saturate' the drag reduction. Once you've achieved attached flow there, no amount of further softening will lead to additional drag reduction.
In wind tunnel footage, provided by Honda, you can see the streamline filaments displacing around the Insight long before they actually reach the car's nose. It's called a 'surface of discontinuity', penned by Ludwig Prandtl, of Germany's AVA G'o'ttingen.
The car produces a stagnation bubble, which travels along with the car, which in itself, will produce a quasi, half- convex- hemispherical nose out of the atmosphere, extremely resistant to separation, up to 250-mph.

[aerohead]

Originally Posted by Tahoe_Hybrid

would that void the warranty... you could do a ultra light trailer 1k pounds is the limit.... you will be limited to 55mph in most areas

I looked over at the Tesla site, and they're talking about a 2,000-lb trailer capacity.
If we take 15% of the trailer weight as a recommendation for hitch load, then it seems reasonable that a receiver-hitch-mounted boat-tail could handle a GVR of 300- lbs.
Since it's not a 'trailer', it ought to be immune from trailer towing speed limitations.
Personally, I'd never hang that much weight behind the bumper, same as I'd never speed in Jay Leno's Tatra - 87.
Cd 0.19 in a Model 3 would be interesting.

[freebeard]

Originally Posted by radioranger

Gotta point there, I guess another way is to duct air from a high pressure area to a lower one, sort of how they cooled the engines in the Shelby Daytona Coupes, cant think of any ordinary cars that do that , probably because of weather issues, I was also wondering if anyone has tried to relocate their mirrors to the door so the air can flow around the windsheild better, maybe sit the mirror out of the main air flow, maybe back a bit....

• A modern car underbody is a plenum [considered with the road surface] that mangles, or sorts and orders, the airflow from the front and sides out the rear.
  
• 1940s peep mirrors and newer buses and firetrucks with forward-reaching stalks.

Originally Posted by aerohead

Technically, it should make no difference. According to the literature, it requires very little leading edge radii on an automobile to fully 'saturate' the drag reduction. Once you've achieved attached flow there, no amount of further softening will lead to additional drag reduction.

• Cybertruck chamfers.

[bnmorgan]

We wouldn't be able to utilize this phase differential on an automobile, as the atmosphere is always in gaseous phase.

wonder if plasma is an option

[freebeard]

Blue glowing Koenig-Fachsenfeld edges.

[aerohead]

Originally Posted by freebeard

• A modern car underbody is a plenum [considered with the road surface] that mangles, or sorts and orders, the airflow from the front and sides out the rear.
  
• 1940s peep mirrors and newer buses and firetrucks with forward-reaching stalks.

• Cybertruck chamfers.

Yes. The Cybertruck forebody extends to the cut line between the two doors and roof apex, and this entire region is within a very favorable pressure gradient for the boundary layer, with all the flow moving towards a pressure minimum at the cut line / roof apex maximum cross-section.
There should be separation just behind the chamfers, then almost immediate reattachment beyond the locked-vortices traveling with the truck.
Same for the roof apex and 'skid-plate' area.

[aerohead]

Originally Posted by bnmorgan

wonder if plasma is an option

NASA has already experimented with it on aircraft and abandoned the effort.
Aerodynamic drag on aircraft is ruled by surface-friction drag. Zero flow separation is presumed.
Automotive aerodynamics deals with bluff bodies and drag is dominated by pressure drag due to flow separation.
Even if you could eliminate the approximately 12% of surface friction drag on an automobile with plasma, it would do nothing for pressure drag. And it would increase the pressure drag, as you'd be killing the very turbulent boundary layer which is responsible for the low drag turbulent boundary layer responsible for attached flow.
I essence, you'd be taking the dimples off the golf ball. Bad! Really bad!