Lamellar self-blocking grille

[cfg83]

Hello -

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



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


CarloSW2

.

[lunarhighway]

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

opel insignia

vw golf... angle looks wrong though

opel corsa... not very noticable, but that might just be why it's there


mercedes B class... but a lot of curent gen mercs have a similar layout


citroën C3... best example so far

[lunarhighway]

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

[cfg83]

lunarhighway -

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



CarloSW2

.

[lunarhighway]

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

[TestDrive]

Originally Posted by cfg83

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

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 -

- 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.

[cmroseberry]

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.

[lunarhighway]

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.

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


citroen AX

peugeot 205

[cmroseberry]

Originally Posted by lunarhighway

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?

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.

[Frank Lee]

Originally Posted by cmroseberry

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.

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.