Lamellar self-blocking grille
 

This is my attempt to get an image up for lunarhighway for the self-blocking grille.If it works,it will be a photo of the article from POPULAR SCIENCE which includes an image of the high-tech grille.

http://ecomodder.com/forum/attachmen...0&d=1239473349

aerohead -

I got it. It's a very clean image. Thanks!

CarloSW2

thanks a lot! ever since this idea came up i've been looking out for hidden examples of this, and i've seen quite a lot of grill designs wich suspiciously resemble this design...

Thanks for posting!

I KNEW I'd read about Ford's grille and seen an illustration, but didn't have it in my archives and didn't find anything Googling for it.

The suzuki sx4 has a similar concept i think: Suzuki Auto / SX4 Crossover

ollie

Hello -

For our purposes, does the scale have to remain the same? Can we have different scales as long as we maintain the same proportions of angle and shape relative to the oncoming air?

Can the shape be simplified to being just a curve? That would make manufacture easy. Just cut up some tubing and install at an angle. I am guessing it *does* need the "fatter bottom", because it looks like an airfoil.

CarloSW2

vtec-e -

I believe that. It's a joint venture with Fiat, so I wouldn't be surprised if they integrated that kind of aero-trick.

CarloSW2

I wonder if the under/concave side of each foil isn't shaped that way to conserve material rather than being an aero driven design element?

Ease of manufacture for sure has a lot to do with the way it is.

Why shape it otherwise?

Hello -

I tried to do a "proportions and angles" analysis :

http://ecomodder.com/forum/attachmen...1&d=1239519096

Assuming it needs to be in it's original scale, we only need one real dimension to make one.


CarloSW2

.

i've looked for some pictures of car that MIGHT use this... perhaps some only use this effect partly... perhaps designers don't want to deflect away all air
http://i77.photobucket.com/albums/j5...1c0887ee19.jpg
opel insignia
http://i77.photobucket.com/albums/j5...olf-MK6-1c.jpg
vw golf... angle looks wrong though
http://i77.photobucket.com/albums/j5...l_corsa_02.jpg
opel corsa... not very noticable, but that might just be why it's there

http://i77.photobucket.com/albums/j5...bclasscomi.jpg
mercedes B class... but a lot of curent gen mercs have a similar layout

http://i77.photobucket.com/albums/j5...ill/214857.jpg
citroën C3... best example so far

cfg83

your measurements come close to the 30degrees and 21 degrees originally mentioned

i think the distance between the wings contorlles the ammont of air that still passes trough, and the same of the airfoil how soon the air stalls and how big the separation bubble will be.

i've been wondering of the same generall effect can't he reached with a more blunt shape in place of the "wings"... surely a less aero shape should couse an even bigger flow sepparation.... wich could allow for even more space between the slats.

this could put a new light on some bulky looking grill designs that don't look very aero at first sight

lunarhighway -

Depending on the materials, this shape might be easier to fabricate :

http://ecomodder.com/forum/attachmen...1&d=1239523468

CarloSW2

.

perhaps cutting a large diameter plastic drainage pipe length wise to strips is a good idea

Any reason to assume it's a scale drawing and not just an artists rendition?

Aerohead's scanned image is 900 pixels wide, so I'm assuming the scan was done at 120 pixels per inch. If a scan of just the grille and headlight area is done at 300 dpi -
http://ecomodder.com/forum/attachmen...8&d=1239539696
- we'd get a much better look at the actual grille.

The headlights of the period were pretty standard and came in two sizes. These appear to be the smaller ones. If we get a decent view of the grille in the picture, we should be able to make a reasonable guess as to actual size.

I have some doubts about this "lamellar grille" business. I do not see any magical mechanism resulting from the airfoil grille sections. Depending on the vehicle speed and the cooling airflow volume rate, a frontal inlet will take different sized "bites" out of the external flow. The area of the streamtube (a 'duct' with a surface formed of streamlines) entering the front grille will be larger than the grille at zero to low vehicle speeds. At higher speeds, the cooling airflow streamtube gets progressively smaller in area, becoming much smaller than the inlet grille area. I have seen this using smoke with my wind tunnel models; at high speeds there is only a small area in front of the cooling inlet opening where the smoke will actually go in. So at high vehicle speeds, most of the airflow in the vicinity of the frontal inlet is actually "spilled" outside the opening. I would imagine that there are some grille configurations that spill with less drag than others.
I remember an anecdote from a Ford aerodynamicist who was shocked by the ignorance of a manager who suggested a car model should have a "lamilar flow grille" rather than using the correct word: laminar.

so would it be correct to say that any grill will take in less air as speed increases, and more air goes over the car?

i found two more interesting grills seen on older citroen and peugot models from the 80 and early 90's
both seem to have blocks in place the the airfloils... given the the area between the blocks is equal to the frontal surface of the blocks... to me it seems these might behave similar

http://i77.photobucket.com/albums/j5...20080320-1.jpg
citroen AX
http://i77.photobucket.com/albums/j5...Color_Line.jpg
peugeot 205

No, this is not correct. The volumetric flowrate of the air captured by the inlet generally increases somewhat with vehicle speed. Volumetric flowrate = velocity * area. Think about how much flow area it takes to recieve 1 cubic meter per second of cooling air at a vehicle speed of 10 m/s as compared to a speed of 1 m/s.

Actually, "lamellar" is the correct word; in this context it roughly could be called "the shingling effect" via the blades of the grillework arranged the way they are.

So, too bad, Dilbert was wrong this time and the manager was right. ;)

Looks like a good idea but it is probably beyond the capability of any DIYer.

You'd have to get the airfoil shape, pitch and spacing JUST RIGHT for it to work worth a hoot.

You could guess, I suppose, but what good is a design based on a WAG?

Oh, I don't know about that. The geometry of it is laid out right in this thread. Can't be that tough.

Do they really have to be aerofoil shaped? Why not just curved flat slats?

I'm sure you could find some product with the right shapes that you can cut to fit your grill opening.

I think it would probably work to some extent even with plain flat bars, angled and spaced correctly.
Rolls Royce silver shadows have a strangely similar setup - only vertical. I know FE was not a factor in that design, but quietness was and they had no lack of aero expertise at the time.

TestDrive -

That's a good question. Because it's all I have to work with, I am just trying to analyze it for what it is (in the hopes that someone will make one).

Hmmmmmm. If you had one of those weather "wind speed indicators" behind a dummy "grill box", you should be able to stick it out the window and see the grill block "close" at higher speeds.

CarloSW2

autospeed did a quite comprehensive article about pressure measurement and even explained how to make a lo-fi pressure gauge with just a bottle and some tubing...
so provided you have a means of measuring the pressure you could do an A-B test where you test the pressure behind the grill with and without certain mods... if you make the airfoils angle adjustable you could even experiment with the optimal setup.

For figures illustrating what I wrote about previously, see
http://etd.lib.ttu.edu/theses/availa...5018971985.pdf
Alternatively, one can google "ram coefficients Pritchard" and find the same thesis. Check-out the figures on pages 6 and 26 (pages 15 and 35 of the pdf file).

First off, you can't "scale" the grille from drawings or pics to suit your car. Even if the principle worked (which I don't believe), the Reynolds number would be wrong and you haven't accounted for the rest of the shape of the nose.

I'm with cmroseberry -- I don't believe the theory that the flow splits differently based on speed. There's nothing in aerodynamic theory or practice that would support this. Yes, I am an aerospace engineer.

Shawn D -

Most egg-salad. I am going to ask my Dad. He worked on Apollo, so I will get (yet) another engineer's opinion.

CarloSW2

It's not rocket science!

Frank -

Yeah, I know, but he designed cropdusters in the 1950's. He knows aero too.

CarloSW2

Just teasing. I want to hear what he says about it!

Yeah, to make it rocket science, you have to add two cups of thermodynamics and a dash of orbital mechanics. I should know.

i believe the only way it would work was if the engine didn't have enough air exits, making positive pressure on the inside thus forcing the air to go upwards(because it can't go inside).

EDIT: BTW, this has almost nothing to do with the shape of the grill, but the shape might help to get the air upwards instead of downwards.

Hi All,

Ya Know, you could put those wings on a spring loaded pivot. Then the faster you go, the more they tilt up. That would accomplish the same thing. Also, if you let then hang down, they keep the heat in when parked or stopped. In a Prius that is good, but might not be for an idling car. The fan would have to be able to pull them back open.

I somewhat confused on how these work. Wings stall at low-speeds. So, at a low speed the seperation point would be way forward and might act to slow flow. But at real slow speeds, the air easily bends around the wing. So, its like mayber there is a speed of minimal flow? But does a multi-winged lifting body have the same characteristics as a wing by itself? These wings might be so close they intefere with each other's aerodynamics. So does that change how they work?

With the pivot, the wings would begin to close, but then they might not close all the way, because the amount of force is dependant on the mass of the air flowing over the lifting surface. As the gap between the wings closes off, the mass of air through decreases, and so does the force. This might be designed to result in a constant mass flow, no matter what the speed. Is that what is needed by a car? Or is there some other function of cooling fluid flow versus speed?

Maybe one does not even need springs. Just weights along the trailing edge. Again, this might be a Hybrid car solution, as the weights holding the grill shut might be a problem for an car idling in traffic after a long run down the highway.

I think the whole point of the thing is to regulate air flow without moving parts and control mechanisms.

the grill being discussed on this topic has no moving parts, no springs, no pivot. Moving ones are easy to understand.

Hi Frank and Junimrox,

Yea, I know. I and thinking why not add them. Might make it to easier to make work without a super computer for the CFD.

Ford can afford the the super computer time to save the $2 per grill in cheap bearings over 300,000 cars ($600,000 saved). But can we afford the $60K program to do that analysis, when $2.00 might be cheaper for us.

I am not proposing controls. Just pivots and maybe some biasing weights.

yeah, alright, for us its cheaper and easier to do, but that is not what this topic is about.

I would expect that Capri grille to exhibit ordinary behavior rather than strange behavior, especially since the airfoil sections would tend to have low flow resistance. My guess is that someone misinterpreted what they saw the smoke doing during a series of wind tunnel tests on this Capri. Probably the first application of the streamtube concept to better explain automotive cooling airflows began with Shaub and Charles in 1980. The PopSci article predates this insight into the flow physics by four years. The narrowness of the cooling air streamtube at high speeds could easily have made it look like the Capri grille was doing some self-blocking. The greater the external velocity (relative to the internal flow velocity) the smaller that special spot upstream of the vehicle will be that will actually carry the smoke into the inlet. I took a look at some of my old wind tunnel test footage where I used smoke. The smoke wand would leave about a 3/8-in diameter stream behind it. With a 60-mph wind, even though the frontal inlet of the model was about 3 inches wide and 1 inch tall, most of the time I could not get the inlet to swallow all of the smoke from this relatively small stream. In addition, I could just barely see the smoke stream spreading just a fraction of an inch from the inlet opening plane. My hollow models were connected to the suction side of a high-pressure blower; I could manipulate the internal pressure and velocity over a huge range. It could be that for the Capri, the smoke did not spread until after the plane of the grille. I did not have any trouble interpreting my wind tunnel tests because I was already clued-in on the streamtube concept and my models had no grille at all at the frontal openings. If the guys running the test on the Capri did not have the engine fan going, then the cooling flow streamtube would be really narrow.
Back in ’76, the interaction between the external flow and the internal flow was not understood – things are way different now.