Trebuchet03's JettKamm (2000 VW Jetta)

[trebuchet03]

Originally Posted by Dieselguru

Seeing how this is my first post, I'll try not to overstep my welcome.

No worries - if you've got something intelligent to say - it doesn't matter your post count... I, for one, am mildly embarassed of my post count.

Originally Posted by Dieselguru

Tre - It would be very interesting to see some of the runs you have done at a little higher speed, say 75 mph (the speed I drive my 110 mile round trip to work every day).

In time.... I'm a bit hard headed to thnk I would get work done while visiting family That, on top of my analness for doing things right have ensured slow progress....

Originally Posted by Dieselguru

If there are gains to be had, they they will show up faster at those speeds. Especially things like VG's.

While true, gains at the lower speed should be apparent. Just not of the same magnitude... As of yet, I have not found a spot that helps (so ramping up velocity just increases magnitude of losses). Mind you, I'm working in 2D (for lack of a suitable 3D model) and flow interactions over the rear of a car are dependent on 3D interactions ("spillage" from the sides of the car). Have I seen gains with VG's in my CFD? No. Am I giving up? No, It's just not priority at the moment.

Originally Posted by Dieselguru

As a side note: probably the reason most people don't see much improvement using VG's is that
1. VG effectiveness increases with speed (need a seperation point, otherwise its just drag)
2. VG placement probably depends very closely on speed (location of seperation point)


Look very closely at the Mitsu report on VG's. In the test setup section (page 2), they mention the baseline speed of 50 m/s (111 mph). if tre's settup is correct, will the seperation point move forward with increasing velocity to somewhat match that of the Lancer (wont be exactly the same, but simular), and will the VG's will become more effective?

1. I tend to agree
2. Not so sure - these things aren't intuitive, so I can't say in any which direction.

Originally Posted by Dieselguru

Tre - if you still taking requests, through higher speeds into the mix and see what happens to some of your results.

At some point, it's coming If I do it, I'll probably introduce more turbulent flow - because laminar flow is not representative of the low a car sees

I see aerohead made a post... I haven't read it yet, but you totally should. Aerohead has a wealth of knowledge that isn't really based on intuition (a very good thing)

[trebuchet03]

Sorry for long post - I want to keep up while I'm away

For a New Beetle, I'd actually recommend a full tapered rear, at least 6 more feet long.

That car is nearly perfect for the tear-drop shape.

But a terrible example of aerodynamics for stability... "Going TT" also applied to the Beetle Hence the necessity of spoilers for the TT and the Beetle - absofreakinglutly necessary With a more gently slope in the rear (to help taper) - this might not be such a big deal, maybe. Aerodynamics are very important, but we must make sure not to lose sight that it's important for more than cutting through the air efficiently

One overriding consideration is that Volkswagen has almost certainly tuned-up this model in the wind tunnel. These Germans know their stuff - Hucho himself may have fine-tuned the Jetta shape. VW engineers are masters in making hardedge, almost boxy shapes aerodynamically efficient through detail optimization. Accordingly, I would bet the flow separates right off the trailing edge of the trunk lid.

There's def. separation shenanigans either on the rear glass or just before (on the roof)... But, I agree with you. The MkIV Jetta has an arguably low cD - low .3's if not .30 (don't recall specifically off hand). I have questioned myself a couple times as to why I'm doing this knowing these numbers From my reading/research (Hucho, etc. etc. etc.), many of the recommended features have been implemented fairly well. At least by naked eye analysis (I haven't actually measured radius to width ratios, etc.).

Based on the CFD from tre and your insight, what in your opinion are good aerodynamic mods for the highly tuned 99-04 Jetta's?

So having just looked at some Jetta photos, and knowing the subtle and easy stuff is already squared away - I would recommend seeing if you can do without the side mirrors. Next, I would consider fairing-in the back wheel wells. Not having a Jetta around to look over, my only other suggestion would be a boat tail to try to reduce the area that the wake projects. Note that these are changes that automakers normally shy-away from because they worry about customer acceptance.

I concur. Fully Fairing the rear wheels is difficult >half the rear wheels extends beyond the bodywork - so you're adding FA while potentially reducing cD. Additionally, the fender edge has been rolled in a quality fashion (no exposed sheet metal edges) with flush well walls making mounting difficult.

I hesitate to recommend a belly pan because I am not sure how it would effect the heat transfer from the exhaust pipes (I would defer to those ecomodders who have tried it). If I had a Jetta to look at, I could evaluate the cooling air flow path and make suggestions. One of these days, I will try to write a general guide to improving the cooling air flow.

A valid concern. VW uses heat shields to slow down heat radiation upwards into the cabin. The Exhaust is inset fairly well. Still on my todo is a belly pan with placed ceramic tiles and submerged ducts for "just enough" airflow. If "just enough" is zero - awesome Alas, the under body design is not conducive to a nice flat panel... Shame on VW for that :/ One day I'd like a thermocouple add in for my multimeter for testing - but for now, the $15 thermistor meat probe has served me well

Seeing that it has been brought-up, I do not agree that hotter exhaust would be helpful (if it makes much of a difference at all). Flow resistance is proportional to the square of velocity.

This is something I have been curious of too.... More velocity means higher head loss (as a function of velocity, density, etc.).... But the question of if the side effects of one outweighs the negative effects of doing so has yet (as far as I know) been empirically addressed....

I know big yachts cover their exhausts (and everything else) with custom blankets - but I'm inclined to believe that's more for sound dampening than anything else. I am aware of header wrap, etc. But I'd feel satisfied with empirical evidence as applied to a fairly stockish road vehicle... Side effects for heat soak, etc. I'll totally buy that - but I'll shoot myself in the foot if I ever think the designers didn't consider heat soak in programming and sensor design


------
Sorry for the slow slow progress My sister is Graduating college (funny: she starts a year after me and graduates a semester before me) So I'll be away... Then holiday stuff, dealing with school stuff, etc. etc. etc. etc. I'd love to keep this project on full boil, but I'm content (at the moment) keeping it at a medium simmer

All that on top of figuring out what I want to do for the rest of my life... My two general paths at the moment are: Figure out work/career OR get a Masters degree in I don't know what yet (probably either MBA, Mech Engineering, Industrial Engineering/Mgmt Systems or less likely but a viable option: something like Industrial Design.

Ultimate dream/goal is to have my own start-up.

[Deezler]

updates.......................... ?

[Vwbeamer]

I'm missing the stock under tray on my car. I hit a dog (RIP) and it damaged the tray. I had to rip it off to get home because it was dragging the ground.

This was befoe I got my scangauge, but I did check my MPG at every fill up. I was expecting a drop in mileage, but the difference was not enough to notice. ( pre scangauge i drove normal and averaged 42mpg)

How much drag does not having it add?

BTW, I plan on adding back, need to find a new one.

Originally Posted by trebuchet03

Mine is completely open - it's how I bought the car I know, it's terrible - when I open my hood and look down, I see ground (I should be ashamed ).

I will, eventually, block the grille's and add the stock under tray.... But it's important to get a baseline. Should someone else want to recreate, I want them to be successful.

I don't want a situation where the "base" is highly modified from stock whereas someone building for themselves doesn't get the claimed results. This is my beef with HHO peoples - "baseline" is nowhere near "stock" condition. Any failure just means you forgot X by those that want to sell you kits (and refuse to get/allow independent testing).



The flow behind a car is dependent on the "history". I'm getting somewhat different results with the engine bay approximation added in.... Flow under the vehicle ultimately ends up behind the car, and capable of interacting with flow that originated from above.... Although, I did add the ground effect at the same time, so I don't know which one is causing the difference


And UGGGH.... I need (rather, want) better hardware

[basslover911]

^^ I don't think it help much, if any.

Now if you had a full under tray then it would make a difference, but the air gets "dirty" anyway after the front so it matters extremely little. If anything, its amking your intake and engine run cooler thus affecting fuel efficiency.

[Vwbeamer]

I had one person tell me that the tray was not there for areodynamics, but rather to catch oil drips.

The idea being that the tray catches the oil and it blows out at high speeds, preventing oil drips in your garage.....LOL who knows.

I will get one when I find one cheap enough.

Originally Posted by basslover911

^^ I don't think it help much, if any.

Now if you had a full under tray then it would make a difference, but the air gets "dirty" anyway after the front so it matters extremely little. If anything, its amking your intake and engine run cooler thus affecting fuel efficiency.

[COcyclist]

The VW engine tray serves several purposes; especially in the diesel it is a sound deadener, it keeps grit and spray out of the engine compartment, and it helps with aerodynamics. The VW is fairly flat bottomed from the engine back, and even has plastic filler panels in front of the spare tire well to smooth airflow in that region. In cold regions the tray helps hold in engine heat- the diesel warms up slowly but gets the best mileage when fully warm. Some VW owners install a metal skid plate in place of the plastic one to protect the engine from chunks of ice and snow on the highway.

[trebuchet03]

I'm ALIVE!

So yes, winter break with family... Freaking Crazy, but I wouldn't have it any other way Progress is slow at the moment, because I have a lot on my plate... A HUGE Lot. I've been working on writing a paper on this subject that will document the entire process and, hopefully, provide some aero insights from a variety of sources.


Not on topic, but a sneak peak in the HPV world (one of the things I've been tied up with the immediate period of time).

[ldjessee00]

Hello,

Now that I have been given the old gas Jetta to drive (while my wife drives the new 09 TDI Jetta), I am jealous and looking at ways to help the old Jetta along. I was rereading this thread and trying to decide what to do first. I think I need to get a scanguage first, as one of the things that has made driving habits obvious is the MPG readout on the new Jetta TDI.

Any suggestions?

LDJ

[Deezler]

ldj, scan gauge is a great place to start. Once you have it reading coolant temp, go for some grill blocks. I see you are in Indiana. You could probably block both the upper and lower grills for 8 or 9 months of the year safely.

Wait, what year is this "old" jetta? Manual or auto?