• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

Fender fresh air vent

I might be way off base here but open your door while driving down the road at 60 mph or so. You will notice the door will not shut on it's own, there is a dead spot where the door will kind of hang open. Where the door hangs is the narrow vacuum of "dead air" surrounding the sides of the vehicle.

If you open the door a little more it will encounter the airstream beyond the dead air zone and becomes very hard to push open, this is how far out your scoop will have to be if you want to generate ram air at that point on the vehicle.

If you want to test the front quarter panel for ram air possibility tape a couple strings of yarn on the side, go for a drive with a chase vehicle and see what happens, then post a video clip on here. You could also mount a yard stick or something to the vehicle hood overhanging the side with yarn attached every inch or so away from the vehicle to see where the airstream cleans up and how vehicle airspeed affects the airstream. I have not done this but I suspect the results might shed light on what is happening to the side of the vehicle concerning airflow.

Just a crazy late night thought :D

Brian
 
Those SS vents probably stick out about an inch.

I agree, they won't work well for pulling in air on the fender, they just don't stick out far enough to be used there.

If anyone does the yarn thing... It might be beneficial to also duct tape some various heights of L-brackets and then tie the yarn to the holes. That way you'd get a better representation of where the good air starts. If I had a better camera (and knew how to post videos!) I'd do it! You could do it on the passenger side and let the passenger film it.

I wonder how much things would change, if at all, when the window is opened?

The "opening the door" idea is a good one. In theory, you should be able to draw a straight line from the corner of the fender to the edge of the opened door. Inside that line (closer to the vehicle) would be the area to avoid - meaning you'd have to get the "scoop" past that area. Keeping in mind that this area will change, depending on speed.

QUESTION: If you go just a tad bit too far, would the door will actually start to be pulled out of your hand (possibly quite forcefully)? In other words, would a low pressure area be created on the outside surface of the door?

A good analogy to this is a boat's wake - or more specifically, the way the water comes off the bow. Both water and air are fluids, although the difference being air is compressible while water, for all practical purposes, is not.
 
a straight line from fender corner to rear door line wouldnt be accurate enough. Air can come back towards the side of the vehicle the further you get back because it will want to occupy that lower pressure area. So it could curve off the front, so might be more like 4" away at the fender, but only 2" at the door. The strings on a stick at the location you want to put a scoop would be good though.

Theres no way you could get the door to pull away from the car by itself. The force from the air is a lot more than the vacuum could be.
 
buddy said:
a straight line from fender corner to rear door line wouldnt be accurate enough. Air can come back towards the side of the vehicle the further you get back because it will want to occupy that lower pressure area. So it could curve off the front, so might be more like 4" away at the fender, but only 2" at the door.
Click to expand...

So, not exactly like a bow wake. Is that because of the compressability of air? Just trying to understand more of this.

buddy said:
Theres no way you could get the door to pull away from the car by itself. The force from the air is a lot more than the vacuum could be.
Click to expand...

Thanks - it seemed a little counter-intuitive as I was writing it, yet at the same time it seemed like "well, maybe...".
 
Its just because a low pressure area will want to be occupied by a higher pressure area, which is how you get the vacuum in the first place. But the airstream has a force that gradually disipates and less momentum than water. Its easier to see I guess, I dealt mainly with airfoils in school testing but this video shows how air follows something aerodynamic, but then shows you what happens when the object get closer to perpendicular to the airstream, like our trucks. Our trucks are about as non-aerodynamic as they get for passenger vehicles with the big flat front.
http://www.youtube.com/watch?v=6UlsArvbTeo&NR=1
 
Thanks, Buddy. I found the "pulsed smoke" especially interesting (even thought that wasn't the point of this "exercise":smile5:). Of course I always knew that the air going over the top of the wing travels faster, creating the low pressure. However, I always thought that it would travel just fast enough to keep pace with air below (which is traveling a shorter distance) and that both streams would exit together. I never knew the upper stream would accelerate so much that it would actually exit ahead of the lower stream.

But, I guess that makes sense since otherwise the upper stream would actually be slowing down immediately upon leaving the wing. I'm sure it does slow back down eventually - but to do it immediately would then cause a problem for the air that is still on the wing as I'm assuming the air on the wing would not flow correctly over the entire wing.
 
Airflow test

Had some time today to play around a bit with the idea of taping yarn to the fender to observe air flow. I taped yarn at 1 foot intervals along the length of the fender. Doubled up around the wheel well with one about 3 inches below the other. Then, using coat hangers I placed a couple tests at 5", 6" and 12" away from the fender to see what the effects of pushing a 3' x 6' wall through the air would look like.

Placed a few on the hood as well to ascertain the effects there as well.

Issues. Strong swirling winds were manifested on the hood even at 55mph.
Bug Deflector?

Observations. Most of the yarn flowed along side the truck with no real drama. There was no real swirling or abnormal flow observed along side the fenders on the surface or at the coat hangers.

Hood...in a word...weird. yarn flowed out of the hood vents initially but one was pulled back into the engine compartments. Hood surface observations were inconsistant. Any one piece of yarn would flow perpendicular to travel, flow forward, spiral into a coil... you name it.

Hope the videos from you tube are accessable.

http://www.youtube.com/watch?v=BEe3nhDPubw
http://www.youtube.com/watch?v=ihCFHSZHe1A
 

Attachments

  • DSC00271.jpg
    DSC00271.jpg
    42.5 KB · Views: 6
  • DSC00267.jpg
    DSC00267.jpg
    43.5 KB · Views: 5
  • DSC00269.jpg
    DSC00269.jpg
    40.4 KB · Views: 5
  • DSC00270.jpg
    DSC00270.jpg
    45.1 KB · Views: 6
Very interesting, Paveltolz. Thanks for taking the time to do that!

It's interesting to see that the 12" piece is nice and straight, but the 5" & 6" pieces appear to be getting less "good" air. I would of guessed that they would have been far enough out to be nice and straight just like the 12" one.

The ones right on the fender did exactly as most have thought. There certainly wasn't nearly enough air there to term a fender intake as "ram". They were just dancing lazily around - no real rhyme or reason to what they were doing.

It appears to get a "ram air" effect from an intake mounted on the side of the fender that it would need to be mounted somewhere between 6" and 12" away - and that just isn't realistic.

Thanks again!:thumbsup:
 
On another note, I would think cutting a port under the passenger turn signal to "duct" the high pressure air built up at the front of the truck directly into the fender vent might be beneficial...

For example (photoshopped):

38332610001_large.jpg


Or you could probably just build a duct to grab some air from the bumper hole to direct it right into the OE fender duct. Not being a completely "sealed" system would have minimal effect of increased pressure, but it may have beneficial effects in lowering IAT some.

Just something else to ponder....

):h
 
Yes the photoshopped vent would be much better. Some people have done such things like trimming the plates around the lights so they just had the four corners to screw them on.

Someone that has left a side window on a camper open while driving on the interstate needs to chime in on the effects of the airstream
 
I personally dont think a NACA duct would work on our fenders. I think some people misuse them. They work really well on a curved/angled surface, a surface which air will follow the surface of the object. So the air would flow into the duct while disrupting laminar flow as little as possible. Compared to a scoop, which is necessary to get into the airstream on a car that does not have a angled nose/hood like a late nineties camaro, the one on my avatar. The air pushes that car to the ground at high speeds because its like a big spoiler that air follows the surface of the vehicle.

The problem arises when you have a large flat front that has to displace a lot of air away from it.
 
More importantly than the ram air effect on the fender vent, there seems to be absolutely no negative 'venturi' babble effect. I still think with the turbo, no RAM is necessary, and having the the airfilter draw fender fresh air from about 3 inches away will be better than the ducting through the fender.

Don't forget, the fender gets hammered with fanwash, so whatever air passes through it, gets pre-heated. The less time its spent in the fender duct, the better IMO.
 
That's kinda where I'm at. That snorkel was clearly restrictive. I believe there's compression on the fender and a boundary layer that would provide a small level of pressurization. I believe me fender vent is just allowing a cool air supply and relatively free of water intake. I wasn't out to pressurize the intake...just free it up.
 
Matt Bachand said:
More importantly than the ram air effect on the fender vent, there seems to be absolutely no negative 'venturi' babble effect. I still think with the turbo, no RAM is necessary, and having the the airfilter draw fender fresh air from about 3 inches away will be better than the ducting through the fender.
Click to expand...

I dont think you interpretted the "test" results adequately. There is indeed a venturi effect going on, showing there was not the same airstream next to the fender as several inches off. Its not theoretical its just how it works. You will notice the ones taped to the fender dont fly back hortizontal and flounder about a lot. The ones out 6 and 12" hold steady straight back.
 
You must log in or register to reply here.
Back
Top