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-   -   Car face/nose/bumper cover aerodynamics (https://ecomodder.com/forum/showthread.php/car-face-nose-bumper-cover-aerodynamics-1749.html)

Otto 04-07-2008 12:46 PM

Car face/nose/bumper cover aerodynamics
 
Does anybody here know of any studies or designs that optimize the aerodynamics of a car face/nose/bumper cover?

As the surface that first meets the oncoming airstream, the car's face is probably the most important feature for aerodynamic efficiency, just as the leading edge of an airfoil is the most critical part of a wing.

The face has to house and position the cooling inlet(s), headlights, turn signals, and perhaps spoiler/splitter/wheel fairings/deflectors.

So, what face(s) are most efficient? Got pics or cites?

I may re-do the face on my old Porsche 944 Turbo, and would like some good benchmarks as design cues. Suggestions?

Daox 04-07-2008 01:03 PM

The front really isn't as important as the back to be honest. Relatively small changes to the radius transition from the bumper cover to the hood keep the airflow attached. The same can be said for the transition between the bumper cover and underside (assuming your using a bellypan) and sides of the vehicle.

If you post some pictures we can recommend some things probably.

Otto 04-07-2008 01:31 PM

Quote:

Originally Posted by Daox (Post 18323)
The front really isn't as important as the back to be honest. Relatively small changes to the radius transition from the bumper cover to the hood keep the airflow attached. The same can be said for the transition between the bumper cover and underside (assuming your using a bellypan) and sides of the vehicle.

If you post some pictures we can recommend some things probably.

I dunno. In aircraft (especially sailplane) design, the nose contour and texture is quite critical, as buggered airflow there means the rest of the plane is moving into already turbulent and detached flow. The more recent Porsche designs such as Carerra GT and 911 series feature smooth and conformal lines from the nose stagnation point on back, for the best penetration.

I'm not good with posting pictures, but will try and put one up.

Basically, I'd like to consolidate all drag and turbulence-makers such as turn signal lenses, headlights, etc. into streamlined and conformal locations, and have one cooling inlet at the stagnation point, rather than separate intake holes here and there. In other words, as little form drag as possible, although bug splatter and rock chips are a given that eliminate any laminar flow. Turbulent but attached flow seems possible, though, with efficient contour.

basjoos 04-07-2008 09:02 PM

The nosepiece I put on the front of my car made a noticable improvement in coasting ability (this was in my pre-SuperMID days). It also reduced the number of smashed bugs and birds on the front of my car to almost zero (prior to this I was always having to scrub dried bugs and occasional feather off the flat front bumper).

Otto 04-08-2008 12:09 AM

Quote:

Originally Posted by basjoos (Post 18367)
The nosepiece I put on the front of my car made a noticable improvement in coasting ability (this was in my pre-SuperMID days). It also reduced the number of smashed bugs and birds on the front of my car to almost zero (prior to this I was always having to scrub dried bugs and occasional feather off the flat front bumper).


Got pics?

The streamlined nose sheds the stagnation air better, making for a smaller stagnation point in the first place. Good shedding of stagnant air is why your car collects few bug splatters, and also why your car is about as efficient as any car ever was.

The ultimate in efficiency is a high performance German sailplane, such as an ASW-22. They pay great attention to forward fuselage design and contour of the nose, since the rest of the aircraft follows in the wake of the nose. Same story with boats. The nose is the most critical part.

So, who has nose mod suggestion or scientific data?

SteveP 04-08-2008 12:07 PM

You have to be very careful when transferring your knowledge of airplanes to cars.

Airplanes (especially sailplanes) are highly optimized to begin with--they've already taken care of a lot of the base drag by tapering (boat-tailing) the wings and fuselage. That hasn't been done with cars (to the same extent). Accordingly, it is worthwhile *on an airplane* to spend a lot of time on the nose because they've already taken care of the all the parts that are worse.

Second, when it comes to wings (and even the nose), the airplane folks care about lift and are usually trying to either maximize lift (which we're trying to minimize if we even care at all) or maximize the lift/drag ratio. We're (usually) just trying to minimize drag. The difference in goals affects the approach one takes--it may well be the case that the front of the wing (given what I've said above about the trailing half of the wing) is (now) the most important area from the point of view of *lift*. It is clearly *not* the most important part of a typical car from the point of view of *drag*--the rear is because (generally) the largest single drag compoent is base drag.

Third, when you consider the front of the car, you can't just optimize that part in isolation from the others--as you point out with airplanes, what happens there affects what happens downstream. Aerodynamicists treat the front of the car as an integral part of the whole and when they consider mods to the front, they consider what it does to the air flow (and therefore the drag and lift) elsewhere. It is often the case that by making the front have a lower Cd (considered in isolation), they affect the airflow around the car (and especially under the car) in ways that *increases* the drag elsewhere. You have to treat the whole car as a *system* and optimize for overall reduction of Cd.

Fourth, for the reason I just mentioned, there is likely no one *optimal* front end design--there are front ends that work well with particular "back ends" (the part from the front axle all the way to the rear) and front ends which don't. The front end design you pick will depend, in part, on the back end you already have (or plan to make). This is true also with airplane wings and airplane fuselages: you can't just take the front end of your sailplane and put it on a Cessna and expect it to produce good results. Ditto for the leading edges of wings--the whole wing, the whole plane has to be considered.

--Steve

basjoos 04-09-2008 04:33 PM

[QUOTE=Otto;18395]Got pics?

The streamlined nose sheds the stagnation air better, making for a smaller stagnation point in the first place. Good shedding of stagnant air is why your car collects few bug splatters, and also why your car is about as efficient as any car ever was.
QUOTE]

Here are some pics of my car. The stagnation point is 12" above the road. The radiator air inlet is that little slot next to the passenger side headlight in the first photo and goes about 2/3 of the way between the two headlights.

http://img.photobucket.com/albums/v4.../CivicView.jpghttp://img.photobucket.com/albums/v4...vicNewSide.jpg
http://img.photobucket.com/albums/v4...vic/Above5.jpg

Also someone asked in one of the recent threads why many front wheel spoilers/air splitters deflect the air downward rather than from side to side. Splitting the air would be somewhat more efficient (except for the slight increase in interference drag with the underside of the car) than compressing the air downwards against the road. But a pure side to side air splitter (shaped somewhat like the mini-boattails behind my rear wheels) would be less forgiving of impacts with road debris. The ideal shape would be a rounded cone of a rubbery material, but the one on my car is a flared rectangle for ease of construction out of coroplast (I used coroplast rather than aluminum sheet for underbody structures ahead of the wheels for its resiliency to impacts with dead possums and the like). This pic is an older one taken before I converted the nosepiece from coroplast to aluminum.
http://img.photobucket.com/albums/v4...ivic/aero8.jpg

aerohead 04-09-2008 04:52 PM

Car face/nose.......................
 
Hucho's book has the complete development of the "ideal" nose by Volkswagon,including windtunnel photos.Chrysler Aerospace beat them to the punch in 1967,when they developed the front for the NASCAR Dodge Daytona which swept the field.MG beat Chrysler in the 50s with their EX "pumpkin seed".Bucky Fuller beat MG in the 1930s.The list goes back 500-million years.Go to an Asian market and buy a frozen mackeral.That fish will tell you all you'll ever need to know about streamlining.

fabrio. 04-09-2008 07:37 PM

All you have write rigth, and all considerations about the importance fo rearend compared whit the frontend are on line wiht theories.
but the Otto dubts does are infondati.

Perhaps, Otto intends to say that the drag contribution of frontend includes also the interference of front wheels and cooling, not only the dynamic pressure.
I would like to ask at Basjoos, what would happen to his FE if he would remove all changes at frontend, and what would happen to his FE (or Cd) if he would remove all mods at the rearend.

fabrio. 04-09-2008 07:50 PM

Otto, Which model of 944, have you?
I you are problem to put image of your car, link the image from this site: http://www.marcel.nl/944/

Otto 04-09-2008 07:57 PM

It looks just like this, Fabrio.
 
http://www.marcel.nl/944/1034846935.jpg

Porsche 944 Turbo

Has wheels like this one:

http://www.marcel.nl/944/951_side_lg.jpg

The nose got broken, and I am thinking about making a new one with smooher lines, and no bumps. The cooling inlet would be one eliptical hole at the stagnation point rather than all of those narrow holes.

trebuchet03 04-09-2008 10:50 PM

Otto....

I say go for it - do a little research and see what you find... Look for cars with low cD values and start there....

But, I agree with SteveP. It's important, but look at the relative impact. A sailplane is, as Steve said, highly optimized in it's current condition. No doubt, much of their aero problem spots come from their leading edge. As cars are bluff bodies (exception for basjoos perhaps), the trailing surfaces have a much higher significance. Sailplanes are not bluff bodies - which is why their leading surfaces are more important (ditto for solar cars, velomobiles, submarines, etc.).

Now all that said - just because I agree with him... That's not me saying not to do it. If you've got an opportunity to clean something up - I say go for it. You'll no doubt make a difference :p

Otto 04-10-2008 01:38 AM

Quote:

Originally Posted by trebuchet03 (Post 18765)
Otto....

I say go for it - do a little research and see what you find... Look for cars with low cD values and start there....

But, I agree with SteveP. It's important, but look at the relative impact. A sailplane is, as Steve said, highly optimized in it's current condition. No doubt, much of their aero problem spots come from their leading edge. As cars are bluff bodies (exception for basjoos perhaps), the trailing surfaces have a much higher significance. Sailplanes are not bluff bodies - which is why their leading surfaces are more important (ditto for solar cars, velomobiles, submarines, etc.).

Now all that said - just because I agree with him... That's not me saying not to do it. If you've got an opportunity to clean something up - I say go for it. You'll no doubt make a difference :p

If you look at the nose of the Porsche, as seen in the first photo of my post just above, you will see that in front of the hood are the pop-up headlights, a header panel between the headlights, and the bumper cover below. These got whacked when my kid got crossways with a guard rail. If you look closely at the lower photo, you will see that the bumper cover has a sort of step before the contour goes up onto the header panel, rather than a smooth, continuous curve. Aesthetically, this is the only part of the car I don't like. It is sort of like Carmen Diaz' broken nose--just does not look right, or match the lines of the car. Aerodynamically, this can be improved, especially since the fog lights and turn signal lenses are recessed about 1/2" into the bumper cover. (They could be made flush by using spacers.) Those fog lights often are cracked by rocks, so this is not a good place for them to be. The inlet slots feed cooling air to the radiator and to the turbo intercooler. Ducting in is good, but the factory neglected the outlet ducting, so the cooling air is supposed to find its way back into the slipstream somehow.

So, I've considered gluing extruded foam onto the front bumper, then carve and contour it using the lines of the hood and side panels, down to a nice rounded nose at the stagnation point. Then, make an eliptical inlet (long axis of the elipse horizontal), so that the one inlet feeds both radiator and intercooler, as well as oil cooler below, including proper ducting to feed the used air into the front wheel wells. The intercooler sits under the header panel, a few inches in front of the hood. It has a very good diffuser inlet duct, fed from the upper slot on the nose, but has no particular outlet duct. So, I figure making a cowling flap (like in reciprocating engine aircraft such as B-17 or P-47) that is hinged about 4" in front of the hood. Due to air accelerating over the hood, this would be the lowest pressure spot on the car, whereas the inlet at the stagnation point on the nose is the highest pressure point. Fish gill--high pressure in, and Bernoulli suction out and over the hood. This would also bleed off underhood air, which gets heated by the exhaust manifold, etc., and keep underhood temperatures significantly lower. Bernoulli will probably open the cowl flap, but if not, a simple cable arrangement would work. This car also has ducting to cool the front brakes, and that would also be fed from the one eliptical inlet at the nose. Being smooth and with gentle contour, I think such new nose would have significantly less drag than the stock one. And, I would eliminate the pop-up headlights, which are turbulators and speed brakes when up. Instead, covered headlights in the fenders, like Jag XKE or Porsche Boxster.

Combined splitter/front wheel fairing at each front front corner, rather than a single piece type. The Calibra type would probably work and look good. Being two pieces, cheaper to replace if one hits a curb while parking.

Basjoos' car tells us a lot. Even though it has significantly more wetted area than stock, and even though it has some rough edges due to Coroplast, it gets radically better fuel economy than stock, and stock was good to begin with. This says to me that form drag is much improved by Basjoos, even though skin friction was more, for a gross net improvement. Some may say that most of his improvement is due to the extended tail, and maybe so. Still, I cannot help but think his nose job is also a major improvement. I wonder if Basjoos has tested his car with and without the new nose, but keeping the tail. That would be very instructive.

Note the wheels in the silver Porsche 944 Turbo in the second photo. That's what I have. ~30 of us did a 500 mile ratrace through British Columbia several years ago, partly in the rain and mist. You could see the spray and bow wave from each car, as well as its mist wake. Cars were all the same unmodified shape, but wheels were various Porsche types. Mine had the least wake and turbulence off the wheels, by far. Other open-spoke wheels acted as turbines and threw a lateral column of mist ~3-4' aout from the wheels and disrupted the slipstream.

The "flag" mirrors could stand a lot of improvement, and many Porsche guys replace them with "aero" mirrors off the newer 911 cars. I have a set, but have not put them on. I may design my own, using smaller aero mirrors from a motorcycle, and airfoil-cross section stalks, further back from the A pillar.

BTW, if the car is moving along at, say, 60 mph, that means the air flowing over the hood and past the mirrors is going a LOT faster than 60 mph. Sticking a mirror or other obstruction into that high speed air means exponentially increased drag at that location. The extra drag and turbulence makes noise, right next to your ear. Ungood.

jazzie604 04-10-2008 09:53 PM

what effect does the ground play in all this aero talk? a plane has the benefit of a couple thousand feet under it to play with, while cars have to compress or divert all of that air out of the way.

SteveP 04-11-2008 09:50 AM

Re ground effect:

as far as I know so far (and I'm willing to be wrong about this), it affects the airflow under the car, but doesn't have much affect on the air flowing around the car or over the car. The flow under the car is being discussed in depth here:

http://forum.ecomodder.com/showthread.php?t=1783

--Steve


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