Tailgating a lorry/semi (modelled in CFD)

[Piwoslaw]

This thread was supposed to be about modelling the aerodynamics of drafting a semi.
Iirc, there are other threads which discuss the safety of such driving.

[TEiN]

Originally Posted by UFO

Mythbusters showed ...

Mythbusters = Entertainment Masquerading as Science.

[sendler]

Originally Posted by TEiN

Mythbusters = Entertainment Masquerading as Science.

Often though provoking, you must admit.

[UFO]

Originally Posted by TEiN

Mythbusters = Entertainment Masquerading as Science.

I don't disagree, but many drafting advocates base their position on their data; until better data comes along, theirs seems plausible enough.

[Piwoslaw]

Originally Posted by UFO

I don't disagree, but many drafting advocates base their position on their data; until better data comes along, theirs seems plausible enough.

More like: Until better data hits mainstream entertainment...
Just because better data exists doesn't mean that people will look for it, or even notice, unless it's wrapped up all nice in sugar and has an easy to swallow coating.

Now, back to CFD modelling...

[ProDarwin]

Originally Posted by redpoint5

Drafting a lorry seems relatively safe to me. While you cannot come to a stop within 100ft of distance, neither can the truck unless he hit a concrete wall. All of my vehicles can stop much, much quicker than a semi. Besides that, they only travel 60mph tops where I'm at. This isn't nearly as dangerous as those that tailgate doing 85 in the fast lane.

My car will stop in just over 100ft at 60mph. On the factory (crap) tires. My other car is much worse at 189 ft from 70 on factory (crap) tires and factory (crap) brake pads. I'd put it close to 130ft now. A semi braking distance from 65mph is over 400 feet. http://utahmc.com/trucksmart/trucksm...-factsheet.pdf

Additionally, on a semi there is a delay between when the brake lights come on and the brakes are actually applied. Air brakes have a significant lag (you can read the limits of it in the FMVSS standards).

[Cd]

O.K.

So...back to the CFD discussion.

What are your machines specs ( Speed, RAM, etc )

Are you using a renderfarm or a single machine ?

Great to see SolidWorks being used here on the site ! Looking forward to more.

[sendler]

Is solid works rendering in 3D? Can you pan the view to see from the top? Can it do an animation with little airborne "bubbles" showing all of the actual flow?

[Old Mechanic]

I think the benefit extends back further than most here might think. I can link you to videos of the Hampton Roads Bridge tunnel cameras where 90,000 cars pass over the same point in a two lane (each way) road in 24 hours. Two seconds ain't working there and thats 24-7 with periods where the separation distances are 3 cars lengths or less.
45,000 cars over the exact same spot, in a single lane, in an 86,400 second day. Do the math, it doesn't work with 2 seconds separation.

AVERAGE FOR HOURS AT 60MPH!

You can forget 2 seconds here. 2 seconds will get you passed on the right by another car in the gap you leave, even on the approach lanes at intersections.

Generally I try to keep 3 stripes between myself and the vehicle in front. 43 feet from the same point to point stripe to stripe, about 100 feet. I find that at that distance I get the same mileage at 65-70 on the Interstate as I get at 55 on the parallel road that has no traffic, over 50 miles of distance.

Another point, the air directly behind the tractor trailer is moving forward, which I don't see in the flow diagram. Since it has to be moving forward or you would be in a perfect vacuum and suffocate, then the flow reversal has to take some time before it occurs, maybe not modelled in your illustration.

regards
Mech

[Cd]

Originally Posted by sendler

Is solid works rendering in 3D? Can you pan the view to see from the top? Can it do an animation with little airborne "bubbles" showing all of the actual flow?

Yes ! True 3D !
And yes you can render animations as well .

Yes, yes, and yes !


If you are a student, you can get an educational copy with a 6mo. license for a hundred bucks !

Educational copies have deep discounts.
I paid $ 300 bucks for a program that cost over $ 3,500 when I was a student.