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 Post subject: Locost CFD
PostPosted: Mon Feb 27, 2012 1:15 pm 
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Always Moore!
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Pe7e's avatar reminded me that I've been meaning to post these for awhile now.

These were done by a friend a few years ago using my original Locost model.

These first ones are of the pressure coefficients at different areas on the car.


Attachments:
cp_side.JPG
cp_side.JPG [ 65.73 KiB | Viewed 3306 times ]
cp_isofront.JPG
cp_isofront.JPG [ 67.22 KiB | Viewed 3306 times ]
cp_front_with_mesh.JPG
cp_front_with_mesh.JPG [ 227.42 KiB | Viewed 3306 times ]
cp_front_mesh_only.JPG
cp_front_mesh_only.JPG [ 185.21 KiB | Viewed 3306 times ]
cp_front.JPG
cp_front.JPG [ 78.25 KiB | Viewed 3306 times ]
cp_back.JPG
cp_back.JPG [ 78.53 KiB | Viewed 3306 times ]

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 Post subject: Re: Locost CFD
PostPosted: Mon Feb 27, 2012 1:17 pm 
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Here are the stream lines (these may be a re-post) showing the path the air is taking around the chassis.


Attachments:
streamlines_rear_iso.JPG
streamlines_rear_iso.JPG [ 91.06 KiB | Viewed 3304 times ]
streamlines_front_iso.JPG
streamlines_front_iso.JPG [ 106.23 KiB | Viewed 3304 times ]
streamlines2_front_iso.JPG
streamlines2_front_iso.JPG [ 128.86 KiB | Viewed 3304 times ]

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 Post subject: Re: Locost CFD
PostPosted: Mon Feb 27, 2012 1:19 pm 
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Always Moore!
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Next are the velocities at different areas on the chassis.

Keep in mind that high velocity typically means low pressure and low velocity typically means high pressure.


Attachments:
vel_top_at_wheel_center.JPG
vel_top_at_wheel_center.JPG [ 66.49 KiB | Viewed 3303 times ]
vel_top_at_headlight_center.JPG
vel_top_at_headlight_center.JPG [ 63.09 KiB | Viewed 3303 times ]
vel_at_wheel_center.JPG
vel_at_wheel_center.JPG [ 56.28 KiB | Viewed 3303 times ]
vel_at_shocks.JPG
vel_at_shocks.JPG [ 69.66 KiB | Viewed 3303 times ]
vel_at_headlights_side.JPG
vel_at_headlights_side.JPG [ 60.41 KiB | Viewed 3303 times ]
vel_at_headlights.JPG
vel_at_headlights.JPG [ 62.69 KiB | Viewed 3303 times ]
vel_at_centerline.JPG
vel_at_centerline.JPG [ 54.98 KiB | Viewed 3303 times ]

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 Post subject: Re: Locost CFD
PostPosted: Mon Feb 27, 2012 1:21 pm 
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Always Moore!
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And finally the velocity boundary layers.

Enjoy. :D


Attachments:
vel_iso_135.JPG
vel_iso_135.JPG [ 54.54 KiB | Viewed 3301 times ]
vel_iso_125.JPG
vel_iso_125.JPG [ 57.11 KiB | Viewed 3301 times ]
vel_iso_115.JPG
vel_iso_115.JPG [ 61.29 KiB | Viewed 3301 times ]
vel_iso_110.JPG
vel_iso_110.JPG [ 60.39 KiB | Viewed 3301 times ]
vel_iso_80.JPG
vel_iso_80.JPG [ 61.18 KiB | Viewed 3301 times ]
vel_iso_50.JPG
vel_iso_50.JPG [ 56.27 KiB | Viewed 3301 times ]
vel_iso_20.JPG
vel_iso_20.JPG [ 57.43 KiB | Viewed 3301 times ]

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 Post subject: Re: Locost CFD
PostPosted: Mon Feb 27, 2012 2:50 pm 
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Does this mean we can expect parachutes to look like Locosts in the future?

That's pretty cool looking stuff. What is the model built with. I don't suppose there is such a thing as cheap CFD software...

I wonder if you built a midi and put the Locost body on backwards how much better it would be. I just have to move the headlights...

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 Post subject: Re: Locost CFD
PostPosted: Mon Feb 27, 2012 3:02 pm 
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VERY AWESOME!!! Lots of food for thought.


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 Post subject: Re: Locost CFD
PostPosted: Mon Feb 27, 2012 3:40 pm 
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Sweet. It looks like the front isn't too bad, but the back could use some help. I'm surprised, I thought it would be much worse.

Can you do that with a brick wall, for comparison :D


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 Post subject: Re: Locost CFD
PostPosted: Mon Feb 27, 2012 5:12 pm 
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You can see why those little wings off the sides of the windshield are such a good idea. Very cool information, thanks for posting.


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 Post subject: Re: Locost CFD
PostPosted: Mon Feb 27, 2012 9:17 pm 
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Wow! That's great stuff. Interesting confirmation (if I understand the data correctly) that the intuitively streamlined nose creates a bit of lift. After all it is an upper-half airfoil section.

Andrew, I'm glad the avatar prompted the post, but I'll change it to avoid any perception of (plagarized) claim of credit. I pulled it out of my "aero" folder as a cool image, but I'd clipped it long before I started trying to tag images with sources. The vel_at_wheel_center image is sublime, though, and I'm struggling with the temptation to use part of it instead. :)

-Pete


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 Post subject: Re: Locost CFD
PostPosted: Mon Feb 27, 2012 10:28 pm 
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[tangent]
I'm sorry, but are you sure you didn't steal a couple of those from the 1970's Lotus design archives?
[/tangent]


Attachments:
locostfro.JPG
locostfro.JPG [ 43.46 KiB | Viewed 3211 times ]
oscargamblefro.jpg
oscargamblefro.jpg [ 17.7 KiB | Viewed 3211 times ]

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 Post subject: Re: Locost CFD
PostPosted: Tue Feb 28, 2012 10:36 am 
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Marcus - I believe parachutes, aircraft spoilers, and many other high drag devices could benefit from borrowing this Lotus design. :D

I used Solidworks to do the original model then I removed all of the parts that were details for construction and gave my buddy a copy of all of the exterior parts to use for Cosmos. I've tried Cosmos before and failed miserably which is funny because I get SW. I guess I never grasped how to properly apply boundary conditions and create a mesh. Oh well maybe someday but I do not think it is one of those things you'll figure out completely after poking around for an afternoon or two.

Adding some sort of rear fairing in the shape you're describing definitely couldn't hurt. Jack's rear end of his Lalo is a testament to this.


Thanks Kart. I'm sure your windshield will do much better in terms of drag than the standard Locost version.


IA599 - I'll see what I can do. I'm guessing the wall won't be much worse. ;)


Firebat - Definitely. Another thing that is interesting about the streamlines is how the air travels down the side of the car, hits the high pressure in front of the rear fender, and makes a 90 degree turn into the cockpit. It makes some sort of half door look hopeful for reducing buffeting.


Pe7e - Yeah you're probably getting a little lift since it looks like there is some pretty high velocity air at the top surface near where it transitions into the hood (I'm looking at vel_at_centerline.JPG - the big spot of red). The air beneath the nose doesn't seem to do the same.

What really makes me cringe is the "yellow" windshield. It isn't the highest pressure on the scale but it is a ginormous area (at least 1/3 if not approaching 1/2 of the car's front plan area). I think removing the windshield would do a nice job at reducing drag.

I really do not care what people do with stuff I post (as long as I don't find it on Ebay for sale under their name ;) ) - if you want it as an avatar go for it. I won't be offended.


Justin - Apparently Lotus was ahead of the times when they designed this car. They figured out the aerodynamic properties of a 70s hair cut in the mid 50s! That Colin Chapman was good.... :mrgreen:

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 Post subject: Re: Locost CFD
PostPosted: Tue Feb 28, 2012 4:04 pm 
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Thanks, Andrew; I'll give this one a try for a while. If it sells, I'll give you all the profits.

-Pete


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 Post subject: Re: Locost CFD
PostPosted: Sun Mar 04, 2012 11:41 pm 
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Since the basic shape has been modeled, it'd be very interesting to compare it to one without the windscreen [or with a stubby "aeroscreen"], half doors and a half tourneau cover - since that's the way most of these are raced - like this :-

Image

I'm looking at ways to decrease drag on mine at the moment.


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 Post subject: Re: Locost CFD
PostPosted: Mon Mar 05, 2012 10:32 am 
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a.moore wrote:
... What really makes me cringe is the "yellow" windshield. It isn't the highest pressure on the scale but it is a ginormous area (at least 1/3 if not approaching 1/2 of the car's front plan area). I think removing the windshield would do a nice job at reducing drag....

It does; I read somewhere that just removing the glass raises top speed by about 6 mph or so. That's huge.

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 Post subject: Re: Locost CFD
PostPosted: Mon Mar 05, 2012 1:25 pm 
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i have left a gap between my rear fenders and the body, i have also moved the rear of the front mudguards back away from the wheels, i added a trunk to the rear of the car and panelled the bottom of the whole car, all in an attempt to reduce drag but clearly, i still have a windshield and open cockpit, so that was a waste of time!

pehaps i should make some doors with sid deflector windows, rake my windshield much more or indeed make it pointed.

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she's up on song the shift was strong in the finals to boot
it's back to the pits and take it to bits and don't forget the shute
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