Quick and very dirty CFD run on the Z

_ace_

Hey guys, I'm an aero/mech engineer by trade and am doing grad school part time. I have a CFD class and didn't feel like doing the work right now, so I threw together a quick and very dirty run of the Z in CFD.

I built the model by tracing the edges of a picture, and the car was at a slight angle. The spoiler is really just a rough guess since the angle made it hard to see. I had an input air of 100 mph (44.7 m/s) and I put the Z pretty close to true scale based on the wheelbase dimensions.

[nerd talk]On the CFD run, the back face is a pressure BC, and the top and bottom are just using symmetry. The fluid field is 1000 inches, with 300 in front of the car, and 250 tall with the car at its approximate ride height from the picture. The red dashed line is the symmetry BC. I used default options on the solver and didn't even look to see what I was assuming. [/nerd talk]

So it's probably pretty far from accurate, but I thought the pictures were still neat.

Here's what the 2D sketch came from, using a CAD program:


Here are the velocity results:



The pressure results:




I thought it was interesting to see the underbody pressure was affected so much by the presence of a spoiler. No idea if it's really accurate though!

kenchan

yah, i learned that racing rc cars. needs rear spoiler at high speeds.

mhcoss

CFD is fun! I took a cfd lab while getting my bachelors in mech eng and loved it!

_ace_

That sounds like fun--I didn't realize they got going that fast! I need to look into a new toy...

Yeah, I'm really enjoying CFD! I've done mostly structures until recently and dabbled in fluids here and there with work, but I've never gotten a whole lot of exposure to it. I think I'll try to do more of it in my career as the opportunites come.



With the real car, I've been surprised at how much difference there is between the negative lift of the 370Z and the small but certainly positive rear lift of my old S2000. Over 100mph it was really striking how much less stable that car felt than this one!

Mike

so, if I were to put two vents in the hood, about 6 inches up from the hood, on the outsides, would air flow through them or would the air just pass right over them? It looks like the most efficient way to route brake cooling ducts.

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alcheng

Not even just the spoiler, the shape of the body does influence the aerodynamic and behavior alot.

And the geometry of the suspension, spring-rate and 'thickness' of the oil use for the shocks, compound of the rubber-tires and the hardness of the insert.... yup, just like setting up a real car...

I remember some of the drivers have a weight measurement board, 4 Digital scale attached to a flat board, to measure the weight distribution of the car.

mmm..... those days......

Ops... sorry guys..... off topic......

_ace_

This crude prediction isn't good enough to tell you anything useful, sorry. If it were right, the plots indicate very little positive pressure except at the very front of the hood near the bumper. (It also says the fangs are a good spot.) While I don't find that hard to believe, this CFD result isn't trustworthy--I didn't even look at all my assumptions, much less verify they're decent and the result is valid.

Have you thought of a test you could do without cutting holes? (I checked and Pitot tube systems aren't cheap enough to be worth messing with.)

You could always put a scoop on top of the vents for track days if it doesn't do enough alone. Use a bigger scoop if you need more cooling that day.

_ace_

Maybe I shouldn't look into RC--sounds like it gets involving pretty easily!!

alcheng

It's an addiction, but a very exciting one.

Mike

thanks, I thought it was probably a low pressure area. there really isn't a good way to run the hoses down from the fangs to the wheel wells. maybe just ducted fans from the engine compartment would be good enough.

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NISSAN: 75 280Z / 86 300ZX GLL /87 Sentra SE / 03 350Z / 23 Z
Porsche: 93 968 / 23 Macan GTS / 93 968

takjak2

This looks great, glad you did with with the nismo ^_^/
I wonder what pressures, or difference, the air flowing across the front splitter, through the radiator and into the engine makes.

Something to possibly look into for Mike or someone else is the paint like fluid used to check aero in Formula1. They "paint" it on to leading surfaces and can see where and how much it flows. Some discussion here.

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ImportConvert

Aero. It's tricky. This flow model is neat, but it's far too simplistic.

Dodge uses a brute-force approach with the Viper, creating massive down-force through gaudy wings.





GM says the hell with it and the Z06 actually creates LIFT.


(C6 Z06 at Nurbugring)

Ferrari is the true master of aero, creating downforce with what looks like zero effort on cars like the F458 by using under-body tunnels and the venturi effect.

I have always liked how Ferrari manages aero, and this is why everyone hires Ferrari to help them with it. They use finesse and artistically create elegant shapes and structures that generate appropriate amounts of down-force for the goal at hand.

kenchan

Indeed! The whole body is like a spoiler.

_ace_

Mike, if you get it working pretty well, please let us know what you settled on with a quick thread!

takjak2, thanks for that thread link--interesting stuff there. I'll be tucking that behind my ear just in case we need any of those methods for work later on!

It's pretty neat to compare the three cars. I laughed out loud at that corvette picture! Well played.

It really surprises me how different the Z feels at speed than my S2000 did due to the difference in downforce--I never realized how important aero is in performance. That and I actually started to spend some time at the track...

m4a1mustang

To be fair almost everyone flies at Flugplatz.

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