remove the alternator and installing it on the front of the car

[MetroMPG]

Originally Posted by noeryan

Thank you Bicycle Bob! I've never seen those before. I wouldn't put a large turbine in front of the radiator and you wouldn't get much out of it but it would be something for nothing ya know?

Except that most ecomodders already significantly limit unnecessary airflow into the engine bay with partial grille blocks (as the manufacturers are beginning to do, more and more).

So it's not really something for nothing to an ecomodder. That "wasted" air has been redirected around the vehicle, so it's not available to spin a turbine of any consequence to the big picture electric needs.

[noeryan]

totally agree with ya metro. But if you are stuck with a vehicle with a blunt front end... putting grill blocks still induces a high pressure area in the front of the vehicle... unless you wanna put a cone like that aerocivic, you're gonna have that area whether you put grill blocks or not.

[Frank Lee]

No, not really...

as long as airflow is attached, the pointyness of the front end shouldn't be an issue. Think of the speeds we are going.

[noeryan]

Well... actually, not really. The reason people talk about attached and separated flow is because of Bernoulli's Principle. Separated flow does not apply to it outside of the separated area.

It states that ..::IMPORTANT::.. in a streamline, faster flow has a lower pressure than slower flow. Here is the equation to further analyze what is happening:

P1 + .5*[rho]*V1^2 = P2 + .5*[rho]*V2^2

P1 = (static) Pressure at point one in the flow
P2 = (static) Pressure at point two in the flow

rho = density of the air (sea level density is roughly 0.0023 slugs/ft^3 english units)

V1 = velocity of air at point one
V2 = velocity of air at point two

Lets examine flow on the front of the car first. The air isn't really traveling at a certain velocity but relative to the vehicle it is. Lets say we're traveling at 102.6 ft/s (70 mph), the air in front of the vehicle does two things. In the middle of the grill, the air gets pushed on by the car and is stopped, around the sides of the grill the air gets pushed away. **Check out the FloWorks model on the main page of the colorful velocity field.. the blue means stagnant or stopped air** If the atmospheric pressure that day was roughly 2116 lbf/ft^2, plugging into Bernoulli's equation we come up with what is called a Total Pressure which amounts to:

2116 lbf/ft^2 + .5*(0.0023 slug/ft^3)*(102.6 ft/s)^2 = 2128 lbf/ft^2 + 0

As the air travels up and over the hood, it is being accelerated (ignoring the stagnant pocket at the base of the windshield). Keeping the front half of this equation, we alter the velocity from 0 where it stagnates at the grill to some value higher than 102.6 ft/s.. w/o calculating it you can see that P2 must be lower to keep both sides equal.

As flow slows down (as with attached flow over the AFT section of an airfoil or any streamlined body) the V2 value slows to close to the V1 value thus bringing P2 back to something close to P1. In a perfect world, the pressure on the back of the vehicle would be the same as the pressure in the front and there wouldn't be any drag!

Where separation comes into effect is when the air is getting decelerated too much coming around the aft section and the pressure behind the car is greater than the pressure on top of the car. Since flow goes from high to low pressure, the air doesn't want to suck down behind the vehicle and separates from the car. This 'high' pressure behind the vehicle is however, not as high as we would like and compared to the pressure on the front of the car it is low. High Pressure in the front + Low Pressure in the back = Poor Aerodynamics.

Putting a cone in the front of the vehicle minimizes the stagnant air region (Total Pressure area). This is why you see rockets, birds, even tuna with pointed front ends.

SORRY SO LONG BUT I HOPE IT HELPS!! Have a great night!

[Bicycle Bob]

[QUOTE=noeryan;86775]
Putting a cone in the front of the vehicle minimizes the stagnant air region (Total Pressure area). This is why you see rockets, birds, even tuna with pointed front ends.

Rockets use pointy tops because they get into compressibility approaching Mach 1. Birds and fish are able to keep their sharp foraging implements aligned with the flow. Streamlined cars have a blunt front end, to establish the boundary layer and accommodate crosswinds. Early NACA wing sections with smaller leading edge radii were slipprier, but easier to stall.

[noeryan]

I believe you are correct. But are you going to be driving your car at 15º AoA? I'd like to see pictures!

[Bicycle Bob]

Haw! I'm glad nobody got pictures of some of those moments. Usually, it is the crosswinds that give me such vectors.

[noeryan]

Originally Posted by Bicycle Bob

Rockets use pointy tops because they get into compressibility approaching Mach 1.

Oblique shockwaves form at the tip at Mach 1 and a nose cone helps minimize its intensity. HOWEVER, check out the recovery vehicles from the early Apollo missions. BLUNT front end, produced HUGE oblique shocks which: 1. gives a buffer space between the vehicle and the high heat shockwave and 2. requires a lot of energy to form thus slowing it down.

If I can find some of my data from the wind tunnels I'll show it to you. It may have been last year or the year before we placed some spherical objects in there. One was a rough sphere, a smooth sphere, a flat plate and a bowl shaped sphere facing the oncoming air and then turned away.

The rough sphere won the contest and between the spheres, the bowl shaped sphere with the concave section facing the wind came dead last.

I'm only posting to try helping if you guys think I'm wrong I won't post the forum and fill it with 'trash'. I think the best way to get through is to do testing and show numbers. I just don't have that kinda cash.

[Bicycle Bob]

The escape rockets were just a hack for safety. The Soviets, by contrast, had really good styling on their stuff, but lost a lot of guys. The U.S. safety rockets hurt performance more than a better-integrated design would have. Even the Shuttle has to throttle back to avoid damage from the relatively thicker air at medium altitudes, and that costs fuel, too. Rocket science is not without compromises.
When seeking performance, it is important not to copy technical features too far out of context. Among the frescoes on the Parthenon, you will find fake peg-heads, as if the marble had been pegged together like the preceding wooden temples had been. To the Greeks, nothing else looked right, even if they knew it didn't matter.

[noeryan]

Didn't know about the shuttle throttling back at low altitudes. Attached with the boosters and all its not the best shape for going supersonic IMO. Throttling back makes a lot of sense.