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Old 02-27-2009, 01:05 AM   #191 (permalink)
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I'm building a tandem seat special, any chance of a cfd analysis? right now it's suck it and see.

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Stephen

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Old 03-11-2009, 01:41 PM   #192 (permalink)
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Quote:
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What program are you running in order to get the 2D wind tunnel information? Is it open source, and can I have it please?

Seriously, you are putting a tremendous amount of effort into theoretical models. I laud you on this, but there is a point when theory breaks down and one must make a physical representation of ones work. I can't wait to see a finished product.
I beg to differ. I am constantly building antennas for amateur radio, and I start with a modeling program (3 actually), because it saves a TON of time. Yes, I agree that modeling programs are imperfect, and that there is nearly always empirical "tweaking" of the finished design needed to get it "perfect". Meanwhile, I know others that are wasting money, time, and materials (read: feeding landfills & producing more toxins & CO2) experimenting with trial & error designs.

I think it's pretty cool that he's modeling on a computer first, ie starting with known science to predict outcomes. As my interest grows in aerodynamics, I'm now looking for free or inexpensive fluid modeling programs.
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Old 03-12-2009, 12:47 PM   #193 (permalink)
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I beg to differ. I am constantly building antennas for amateur radio, and I start with a modeling program (3 actually), because it saves a TON of time. Yes, I agree that modeling programs are imperfect, and that there is nearly always empirical "tweaking" of the finished design needed to get it "perfect".
I originally stated that I agree with the computer modeling in the beginning. It is one of the most important steps to aquiring a valid framework to base one's design on. My original quote below.

"Seriously, you are putting a tremendous amount of effort into theoretical models. I laud you on this, but there is a point when theory breaks down and one must make a physical representation of ones work. I can't wait to see a finished product."

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I think it's pretty cool that he's modeling on a computer first, ie starting with known science to predict outcomes. As my interest grows in aerodynamics, I'm now looking for free or inexpensive fluid modeling programs.
I work at a manufacturer for filter paper and what works on Paper doesn't always work as Paper, if you catch my drift. We are constantly using projections of theories to determine the course we should take, but we have to make actual paper to confirm what we anticipated.

Also, just because it's "known" science, doesn't mean that it doesn't have limits. For example, in chemistry there are limiting reactants. In these reactions, one of the chemicals in the reaction is consumed first and terminates a theoretically perfect reaction. The final yeild is the actual, whereas the theoretical yeild is what was calculated on paper.
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Old 03-12-2009, 12:56 PM   #194 (permalink)
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I don't know how much the state of the art for CFD has changed in the last 11 years (I imagine a lot), but Hucho was a strong proponent of hands-on wind tunnel development/testing in his 1998 book.

I wonder if it is still true that "automobile aerodynamics is still dominated by empiricism, shape optimization in particular".

Don't know enough about CFD to say.
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Old 03-13-2009, 02:00 PM   #195 (permalink)
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don't know

Quote:
Originally Posted by MetroMPG View Post
I don't know how much the state of the art for CFD has changed in the last 11 years (I imagine a lot), but Hucho was a strong proponent of hands-on wind tunnel development/testing in his 1998 book.

I wonder if it is still true that "automobile aerodynamics is still dominated by empiricism, shape optimization in particular".

Don't know enough about CFD to say.
The thought that keeps recycling through my mind is,that the stylist still has domain over the "spirit" of the vehicle form,and the aerodynamicist is allowed a very small degree of freedom to "optimize" what the stylist has created,as long as it does not "alter" the spirit of the car's shape.------------------------- As far as CFD goes,it seems to get better and better,reducing expensive wind-tunnel time,maybe culling it down to final verification.Not too long ago,one of the members posted a thread about MIT solving the spherical-coordinate Navier-Stokes equation,opening the door to really accurate 3-dimentional CFD.
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Old 03-25-2009, 05:47 PM   #196 (permalink)
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The CFD images are very telling.

I wanted to do this for a crossover or small suv to visualize the eddy currents at the back and explore methods to improve the air flow.

Last edited by mikel09; 03-25-2009 at 05:52 PM..
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Old 04-25-2009, 06:36 PM   #197 (permalink)
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Nice ideas, i am searching aerodynamics for suitable roofline improvements for my ev build, your ideas seem well considered and they look good too! archiebell, i may borrow some of them, if i may, based on your results.
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Old 04-25-2009, 08:10 PM   #198 (permalink)
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Roar!

So for all of you, it appeared I went through another stasis phase on the site I tend to look like I dropped off the face of the internet when I get really busy.

Actually, I've been slammed with what should be my final semester, building the best yet human powered vehicle I've ever worked on and other projects I need to finish out

Here's a couple pictures of what has taken most of my time, I might post more details on it later (we did get 3rd in design ).


(I'm inside )


(yes, we had some awesome crashes)

First Place overall Vehicle


Second Place overall Vehicle


Top speed for us on our own short testing track was 36.6 (as piloted by a non cyclist) Top speed vehicle at the competition was over 45mph

Okay, so here's the deal - back on topic.
1. I'm graduating in two weeks
2. I'm not sure what I'm doing afterward (I am considering starting my own {in stealth mode})
3. I'm still very interested in this project however, I need to do some maintenance/repairs first (timing belt, 1 window regulator, a few other misc. bits - I can't complain, I haven't put any money into the car in nearly 2 years).
4. Did anyone pick up where I left off? Honestly, I haven't been following...

Additionally, I met someone (whom I'm now friends with) that's interested in making an aerotruck - completely removing the bed and starting from near scratch. There's other exciting details to this too that I'd rather not divulge now (he drives a TDI, let your mind wander from there).

So, for now, the project is stalled. I am ready to build when funding is available, however. I need to finalize the model, but I have selected the geometry and feature set as a compromise between manufacturing, CFD results, limited cardboard testing and desired safety features. In a few weeks I'll publish my proposed design, dimensions and etc.
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Old 04-25-2009, 11:19 PM   #199 (permalink)
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Do you have Cd values?

Hello, Trebuchet,

I agree with MetroMPG on the function of the center ridge.

I am coming in late on this topic, I think-- Do you have any Cd numbers? If so, how do the modifications compare to the original shape?

Ernie Rogers

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I thought that feature on the 1L was intended more as a spoiler for minimizing yaw in cross wind situations, rather than for segregating flow in "normal" circumstances. Just a guess though.

Good idea taking the bike rack into consideration. Obviously, I can't use my hatchbackrack any more. But I can still stuff my bike inside easily enough.
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Old 04-25-2009, 11:32 PM   #200 (permalink)
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Welcome back, treb! I was wondering when you'd come up for air again.

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