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-   -   Air deflectors on trucks/lorries (https://ecomodder.com/forum/showthread.php/air-deflectors-trucks-lorries-10398.html)

Piwoslaw 09-29-2009 01:58 PM

Air deflectors on trucks/lorries
 
2 Attachment(s)
I've seen air deflectors on the front corners of trucks for years and have always wondered whether they really work.

http://ecomodder.com/forum/attachmen...5&d=1254246211

The above picture shows deflectors not only on the sides, but also above the windshield. Does this help by deflecting towards the rear air that would normally be pushed to the side, thereby gaining forward momentum (sort of like a sail), or is this outweighed by the penalty of extra drag? I've also seen deflectors/scoops on the rear of vehicles, scooping air into the lowpressure zone immediately behind the truck. Would this make sense, or would it act more like a parachute?

I'll add that trucks aren't the only places I've seen side deflectors:

http://ecomodder.com/forum/attachmen...6&d=1254246211German-built Ty2-50 steam loco.

winkosmosis 09-29-2009 05:16 PM

I seem to recall seeing discussion on these things here before. They're supposed to keep airflow attached instead of fanning out and making a virtual parachute (like when you hold a spoon under flowing water)

Cd 09-29-2009 06:45 PM

The Plymouth Superbird and Dodge Daytona had something similar on its' A pillars. ( That is the chrome piece that you can see in the picture :



http://aerowarriors.com/jpgs/88rd30.jpg

I found it interesting that they were removed when the car was run for top speed at Bonneville. Strange, since when raced on the speedways, they kept them on.

Bobby Isaac and his Dodge Daytona at Bonneville-1970 on Flickr - Photo Sharing!

( The above picture is a poor example, but I saw a better picture that clearly showed that there was no chrome deflector there. )

I wonder if the visor style extention did anything good at all for aero. :

http://carphotos.cardomain.com/ride_...0004_large.jpg

Thanks for posting this question - I've wondered the same thing for years.

winkosmosis 09-29-2009 07:11 PM

That visor has a much smaller outlet than inlet. It takes energy to compress air.


I wonder why they took the things off the Dodge to do the speed run. Obviously they had them on for a reason

Piwoslaw 09-30-2009 02:17 AM

Quote:

Originally Posted by winkosmosis (Post 130700)
I wonder why they took the things off the Dodge to do the speed run. Obviously they had them on for a reason

Maybe they only work up to a certain speed, above that there's more drag than gain?

Piwoslaw 10-05-2009 05:23 AM

1 Attachment(s)
I looked into my little book and found a short paragraph on deflectors. It states that these deflectors have the same effect as increasing the radius of the leading edges. In [2], Hoerner gives a reduction of Cx from 0.71 to 0.26 for deflectors on the leading edges of a bluntnose body, and a reduction from 0.58 to 0.27 when used at the rear. Unfortunately, these are only for lab models, and the rear mounted deflectors showed little or no improvement when used on road vehicles.

The effect on drag for front mounted deflectors depends on the aerodynamic situation between the tractor and the trailor. Buckley et al. ([1]) give a 0.05 reduction of drag for a cab with sharp edges and deflectors with 0 degrees of deflection (i.e. parallel to the direction of movement). This reduction increases to 0.25 when the angle is increased to 15 degrees.

In [3] Wysocki researched the aerodynamics of a long-distance bus. Other than changing the front angle and finding the penalty of using side mirrors (8%), he also tested a deflector on the rear, used to scoop fresh air down onto the rear window to keep it clean, finding it increased drag by about 3%.

http://ecomodder.com/forum/attachmen...5&d=1254734354

[1] Buckley F.T., Marks C.H., Walston W.N., A study of aerodynamic methods for improving feul economy, US National Science Foundation, final report SIA 74 14843, University of Maryland, Dept. of Mech. Engineering, 1978.

[2] Hoerner S.F., Fluid Dynamic Drag, Hoerner Fluid Dynamics, PO Box342, Brick Town, N.J. 08723, USA, 1965. (I believe there is a new edition of this book.)

[3] Wysocki Z., Badania aerodynamiczne autobusu PR-110U Jelcz-Berliet - rozkłady ciśnień, Spr. Inst. Lot. 9/BA/78, Warszawa 1978.

guyd 04-14-2013 03:26 PM

wind deflectors on euro style 7.5 ton trucks
 
most 'standard' trucks in the UK (lorries..) have 'wind delflectors' mounted on the front vertical edge of the cab.

http://www.cromwelltrucks.com/userfi.../nx05fnr-1.jpg

if you look to the left of the cab, you can see the effectivly sheet plastic 1/4 circle vertical deflector.

this is almost always described as a device to reduce dirt on side windows.

surely it helps with getting the air round the side? any ideas?

gumby79 05-16-2020 12:27 AM

Quote:

Originally Posted by Piwoslaw (Post 130634)

Quote:

Originally Posted by guyed
if you look to the left of the cab, you can see the effectivly sheet plastic 1/4 circle vertical deflector.

??
The only semicircle thing I'm making out to the left of the cab is the spot / convex Mirror On the passenger side. Or are you referring to what the arrows are pointing to on the front beside the grill above the head lights?
----

Quote:

Does this help by deflecting towards the rear air that would normally be pushed to the side, thereby gaining forward momentum (sort of like a sail), or is this outweighed by the penalty of extra drag?
Primary purpose in my eye , is the your first part of your question. To divert air to the rear. That would otherwisewould go into making a larger dynamic frontal aera.

Quote:

That visor has a much smaller outlet than inlet. It takes energy to compress air.
+1
Agreed compressing AKA working cost energy. But with the right geometry the parasitic loss can be reduced for a net gain as dimminstrated
HEAR.
+Cd*-A can be LESS FUEL
Dose the extra work (+Cd) offset the reduced dynamic A(-A)
For a totle reduction of CdA? That depends on how you design it. I'm willing to put money these pictured on this truck reduced the total.

freebeard 05-16-2020 01:46 PM

Maybe a better term would be quarter cylindrical? As pointed to by the red arrows.

I think it's ineffectual because it just reproduces the existing corner contour and adds interference drag. If the opening faces forward instead of inward (back half of the quarter cylinder), it would function more like an air curtain (and do more on the ends of the bumper at wheel level).

Is the small added frontal area mooted by the cab-trailer gap?

edit: I though some more: It may be effective in cross-wind conditions, ventilating the lee side.

j-c-c 05-17-2020 06:20 PM

Quote:

Originally Posted by guyd (Post 366624)
most 'standard' trucks in the UK (lorries..) have 'wind delflectors' mounted on the front vertical edge of the cab.

http://www.cromwelltrucks.com/userfi.../nx05fnr-1.jpg

if you look to the left of the cab, you can see the effectivly sheet plastic 1/4 circle vertical deflector.

this is almost always described as a device to reduce dirt on side windows.

surely it helps with getting the air round the side? any ideas?

With experience driving a Semi, etc trucks, I think rain water is more the issue rather then dirt.

aerohead 05-20-2020 02:48 PM

deflectors
 
Quote:

Originally Posted by Piwoslaw (Post 130634)
I've seen air deflectors on the front corners of trucks for years and have always wondered whether they really work.

http://ecomodder.com/forum/attachmen...5&d=1254246211

The above picture shows deflectors not only on the sides, but also above the windshield. Does this help by deflecting towards the rear air that would normally be pushed to the side, thereby gaining forward momentum (sort of like a sail), or is this outweighed by the penalty of extra drag? I've also seen deflectors/scoops on the rear of vehicles, scooping air into the lowpressure zone immediately behind the truck. Would this make sense, or would it act more like a parachute?

I'll add that trucks aren't the only places I've seen side deflectors:

http://ecomodder.com/forum/attachmen...6&d=1254246211German-built Ty2-50 steam loco.

The forebody is in the most favorable pressure regime of the whole truck. And we know that leading edge radii constituting a very small percentage of the square-root of the frontal area is adequate to achieve fully-attached flow. Very little rounding will 'saturate' it,with any additional radii returning zero drag improvement.
I don't know what the premise for the deflectors are.They certainly are not necessary for the lowest drag.

freebeard 05-20-2020 04:14 PM

I hadn't noticed the A-pillar deflectors. The one across the windshield is [apparently] translucent. It could be a sun shade for the driver.

I think the locomotive deflectors are done right, although I suspect it was for mitigating the black smoke plume. They will capture more air stagnating on the front and pressurize it.

JulianEdgar 05-24-2020 12:13 AM

Caught up with air guide vanes on a Mercedes.

https://i.postimg.cc/kGC0VcGf/IMG-0415.jpg


Inlet....

https://i.postimg.cc/G3J0WZgN/IMG-0413.jpg

...versus outlet.

https://i.postimg.cc/wMkSDmsH/IMG-0414.jpg

Note how duct converges.

Edit adition: these relative openings (three fingers entrance versus two fingers exit ) are what I settled on with my Edgarwit external air curtains on my Gen 1 Insight. I did a fair bit of throttle-stop testing before settling on those figures.

j-c-c 05-24-2020 08:34 AM

I don't see any comment on the trucks vertical turning vanes cross section uniformity?

JulianEdgar 05-24-2020 05:11 PM

Quote:

Originally Posted by j-c-c (Post 624973)
I don't see any comment on the trucks vertical turning vanes cross section uniformity?

There has been discussion on other threads about whether such ducts should be converging, diverging or of constant internal cross-section.

j-c-c 05-24-2020 06:54 PM

Yes, I am aware of that, but you (?) shared that the truck pictured shared the approx similar converging you used on your test vehicle, but your test vehicle had a varying cross section air foil, and a turning vane in many cases I believe does not have an inherent need for a typical airfoil wing crossection, as it by design has to add drag for little gain, when used symmetrically opposed vertically on the front of a vehicle.

So my question still stands, were the vertical turning vanes on the front corners pictured recently in this thread on the front corners of the semi truck, of a uniform cross section?

JulianEdgar 05-24-2020 07:33 PM

Quote:

Originally Posted by j-c-c (Post 624987)
Yes, I am aware of that, but you (?) shared that the truck pictured shared the approx similar converging you used on your test vehicle, but your test vehicle had a varying cross section air foil, and a turning vane in many cases I believe does not have an inherent need for a typical airfoil wing crossection, as it by design has to add drag for little gain, when used symmetrically opposed vertically on the front of a vehicle.

So my question still stands, were the vertical turning vanes on the front corners pictured recently in this thread on the front corners of the semi truck, of a uniform cross section?

Yes

JulianEdgar 05-25-2020 01:26 AM

Quote:

Originally Posted by j-c-c (Post 624987)
... and a turning vane in many cases I believe does not have an inherent need for a typical airfoil wing crossection, as it by design has to add drag for little gain, when used symmetrically opposed vertically on the front of a vehicle.

I think you are underestimating the low drag of an aerofoil. A good example of equivalent drag of a circular rod and streamlined shape:

https://i.postimg.cc/QVLsXKK3/IMG-0419.jpg

Even when producing lots of lift, the GOE222 aerofoil has drag that is tiny (around 1/70th of the lift force).

I haven't done comparative testing of the aerofoil Edgarwits against curved flat plates but I'd be surprised if drag was high.

(I did do comparative testing of an aerofoil section against a curved flat plate for A-pillar guide vanes, and the curved flat plates didn't work. The aerofoils did.)

But as I always say - I don't have a monopoly on testing. I'd love to see others try some external guide vanes (of whatever design) and report on their drag results.

freebeard 05-25-2020 03:33 AM

I suspect that the leading and trailing edges are significant, but thickness mid-chord isn't.

Piotrsko 05-25-2020 10:10 AM

Gotta stop using those fat ugly gottengen style windmill blade profiles and at least use something like a Selig 737 tailfeather airfoil which are less sensitive to angle of attack and have a lower cd.

JulianEdgar 05-25-2020 04:56 PM

Quote:

Originally Posted by Piotrsko (Post 625020)
Gotta stop using those fat ugly gottengen style windmill blade profiles and at least use something like a Selig 737 tailfeather airfoil which are less sensitive to angle of attack and have a lower cd.

I'd be happy to experiment with different aerofoil profiles if you can find another so cheap and easy to use (eg another extruded aluminum one). The other extrusions I can fine are just generic ie no aero data.

j-c-c 05-29-2020 08:27 PM

Quote:

Originally Posted by freebeard (Post 625006)
I suspect that the leading and trailing edges are significant, but thickness mid-chord isn't.

I agree, but it must also be symmetrical, and chord length at some point becomes a factor in whatever the mid chord thickness is chosen.

All meaning to me, the thinnest possible at the requisite strength is the goal.


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