Feel the draft....FEEL the DRAFT! - Fuelly Forums

Click here to see important news regarding the aCar App

Reply
 
Thread Tools Display Modes
 
Old 07-16-2008, 02:37 PM   #1
Registered Member
 
theholycow's Avatar
 
Join Date: Apr 2008
Posts: 6,624
Country: United States
Send a message via ICQ to theholycow Send a message via AIM to theholycow Send a message via MSN to theholycow Send a message via Yahoo to theholycow
Lightbulb Feel the draft....FEEL the DRAFT!

I got on the highway as usual today, and there was an unusually large traffic quantity. Soon I entered the left lane in the large space between a large tractor towing a short shipping container and a sports car with 4 excessively bright headlights inexplicably turned on, actually managing to provide awful glare on a bright sunny day.

I found that the truck was steadily going about the speed I'd go, and was staying in the left lane instead of moving right as most truckers would do, so I decided I'd try to draft. I figured I'd need to draft closer than usual for such a short truck, and drafted at 1.5-2 seconds.

If you're familiar with containers on trucks, their bodies sit higher than a normal box trailer. The trailer is an independent frame that's pretty high to begin with, and the box sits on top of the frame. This particular one had an abnormally high frame. Looking at it I figured there wouldn't be a good draft since there was almost no truck down at my height, the bulk of it being higher than my hood.

I drafted him for what seemed like forever, until he seemed like he was getting out of my way, thinking I was tailgating pissed off. I felt bad for him, some jerk pulled out of the breakdown lane in front of him, nowhere near highway speed.

Anyway...here's what I noticed about the wind. I drive with my windows open, and usually at 70mph I have steady, comfortable wind. Behind this truck, I was getting rhythmically whacked in the head with bursts of air in a 1 second cycle. Was I in bad turbulence, or was I in a good draft?
__________________

__________________
This sig may return, some day.
theholycow is offline   Reply With Quote
Old 07-16-2008, 02:58 PM   #2
Registered Member
 
GasSavers_RoadWarrior's Avatar
 
Join Date: Feb 2008
Posts: 1,652
I think there's more turbulence on those container trucks due to the ribbed sides on the containers.
__________________

__________________
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice
GasSavers_RoadWarrior is offline   Reply With Quote
Old 07-16-2008, 03:00 PM   #3
Registered Member
 
Loserkidwac's Avatar
 
Join Date: Oct 2007
Posts: 160
Country: United States
Send a message via AIM to Loserkidwac
I know when I would draft in my VX, which i had fairly low to the ground, behind a normal tractor trailer i could feel burst and the car would feel like it was being pushed side to side...I always assumed this was what a true draft felt like since the air seemed like it came around the sides of the truck, not straight on as if no one was in front of me...wouldn't mind to hear some input from someone who has knowledge on this...
__________________
MPG Noob

03 Mazdaspeed Protege
91 Honda CRX Si
95 Honda Civic VX *RIP 5/20/08
94 Honda Del Slow D15z1 Swapped
Loserkidwac is offline   Reply With Quote
Old 07-16-2008, 03:06 PM   #4
Registered Member
 
GasSavers_RoadWarrior's Avatar
 
Join Date: Feb 2008
Posts: 1,652
Vortex shedding off a bluff body...

http://www.maths.manchester.ac.uk/~m...ons/vtran2.mpg
__________________
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice
GasSavers_RoadWarrior is offline   Reply With Quote
Old 07-16-2008, 03:22 PM   #5
Registered Member
 
theholycow's Avatar
 
Join Date: Apr 2008
Posts: 6,624
Country: United States
Send a message via ICQ to theholycow Send a message via AIM to theholycow Send a message via MSN to theholycow Send a message via Yahoo to theholycow
Ah, that certainly explains what I felt. Was I too far back for a decent draft?
__________________
This sig may return, some day.
theholycow is offline   Reply With Quote
Old 07-16-2008, 03:34 PM   #6
Registered Member
 
Join Date: Apr 2008
Posts: 1,264
Country: United States
Location: up nawth
It would be interesting to carry an accurate barometer with you to see where you got the lowest pressure.

Next time try different distances to see what effects you notice.

regards
gary
__________________
R.I.D.E. is offline   Reply With Quote
Old 07-16-2008, 05:07 PM   #7
Registered Member
 
GasSavers_RoadWarrior's Avatar
 
Join Date: Feb 2008
Posts: 1,652
That animation is at a fairly low reynolds number I think, the wake would be 3-4x as long in the 10^5 to 10^6 range.
__________________
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice
GasSavers_RoadWarrior is offline   Reply With Quote
Old 07-16-2008, 06:26 PM   #8
DRW
Registered Member
 
Join Date: Oct 2006
Posts: 615
Country: United States
Von Karman strikes again!
http://www.en.wikipedia.org/wiki/Von..._vortex_street
A Karman vortex can occur after any size object. The airflow meter on my car (and many Mitsubishis) is a Karman type.
__________________
Dave W.
DRW is offline   Reply With Quote
Old 07-16-2008, 07:30 PM   #9
Registered Member
 
trautotuning's Avatar
 
Join Date: Jan 2008
Posts: 135
Country: United States
How does nobody talk about "surfing"?

Seriously it is not as dangerous, no rock chips, and still brings about a lot of gains just look at the sides right around the middle of the shape is where the air separates the most...
__________________
trautotuning is offline   Reply With Quote
Old 07-17-2008, 02:31 AM   #10
Registered Member
 
GasSavers_RoadWarrior's Avatar
 
Join Date: Feb 2008
Posts: 1,652
Quote:
Originally Posted by trautotuning View Post
Seriously it is not as dangerous,
Since I've nearly been merged into by large vehicles over 20 times that I can remember in the last few years, and have never come close to running in the back of one, or being outbraked by one, I'll take that with a pinch of salt.
__________________

__________________
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice
GasSavers_RoadWarrior is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Fuelly iOS Apps
Powered by vBadvanced CMPS v3.2.3


All times are GMT -8. The time now is 11:18 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.