New (free) tech paper

[orange4boy]

Originally Posted by Vman455

And then you reached this conclusion:

I didn't mean that as a conclusion. Should have added an /s. It was meant to jokingly prove a point about semantics and pedantry. I'm poking fun in both directions. A fixed template that claims to solve all problems is obviously not practical or efficacious (not that I ever thought the template was) but output from applied knowledge meant to modify a vehicle can be a template.

(Also, the "context from the experts" you posted refers to the Ahmed body and SAE body, not the DrivAer models. It isn't clear in your subsequent posts that you understood that).

I did and I'm glad the piece was posted.

But the first quote is a caution against using simple bodies to predict flow over a real car because the flow around them is too complex to predict with something like a template. For example, just because a researcher tested a cylindrical body and found that it had lowest drag with a 22-degree taper doesn't mean that a 22-degree taper will give lowest drag on any car.

I agree. I have personally never expected "thee holy template" to do anything more than exemplify one possible low drag shape and, in the absence of something better, ie: CFD and an accurate model of my personal vehicle, to give one a very basic principal shape to keep in your head. At the time I was active, I understood the 22 degree taper to be a rough guide for mods which would then require tuft testing and evidence of mpg improvement.

[Vman455]

Originally Posted by orange4boy

I didn't mean that as a conclusion. Should have added an /s. It was meant to jokingly prove a point about semantics and pedantry. I'm poking fun in both directions. A fixed template that claims to solve all problems is obviously not practical or efficacious (not that I ever thought the template was) but output from applied knowledge meant to modify a vehicle can be a template.

(Also, the "context from the experts" you posted refers to the Ahmed body and SAE body, not the DrivAer models. It isn't clear in your subsequent posts that you understood that).

I did and I'm glad the piece was posted.

Thanks for the clarification; it's very hard to read intention in text. These days I end up editing my replies 4-5 times before I post anything just to try and make sure I'm not coming across as confrontational (hopefully I'm successful!).

Originally Posted by orange4boy

I agree. I have personally never expected "thee holy template" to do anything more than exemplify one possible low drag shape and, in the absence of something better, ie: CFD and an accurate model of my personal vehicle, to give one a very basic principal shape to keep in your head. At the time I was active, I understood the 22 degree taper to be a rough guide for mods which would then require tuft testing and evidence of mpg improvement.

That may have been your understanding, but I'm afraid it wasn't--and isn't--universal. I've linked before to a thread from 2010 wherein several posters speculate on how to "cure" the flow separation over the rear window of a Prius when no such separation exists, a fact revealed by a simple tuft test. They reached that conclusion based solely on visual comparison to the template profile! And that's just one of many examples of the template being used here as the arbiter of aerodynamic performance.

I agree that tuft testing is important. But I disagree that there is nothing between that and CFD modeling that is useful--pressure measurement, direct measurement of lift, throttle-stop testing, etc. can all give us a better picture than intuition, which is unreliable and often wrong.

[JulianEdgar]

Originally Posted by Vman455

I agree that tuft testing is important. But I disagree that there is nothing between that and CFD modeling that is useful--pressure measurement, direct measurement of lift, throttle-stop testing, etc. can all give us a better picture than intuition, which is unreliable and often wrong.

I don't think that orange4boy has been around this subforum much in the last 12 months, when basically all those techniques have been introduced.

[orange4boy]

hopefully I'm successful!).

Yeah it’s all good.

I agree that tuft testing is important. But I disagree that there is nothing between that and CFD modeling that is useful--pressure measurement,

You must have missed the “ie” in my statement. I agree that there are many other ways of testing and coming up with ways of modding. It’s not uncommon for communities to end up with particular methods that become a sort of “tradition”. Ecomodder stickied the template so of course people would see it and be more likely to use it. That’s kind of what I meant by “in the absence of something better”. Lots of people new to aero would see it and use it until they were around long enough to learn more. I toyed with it briefly , just because it was there, but bought Hucho’s fourth edition at the time (as was widely encouraged) and never really paid much attention to the template myself.

And that's just one of many examples of the template being used here as the arbiter of aerodynamic performance.

Thats aero though. My god, chasing down all the misconceptions is a Herculean task! Even the experts disagree on some of the finer points.

Pressure measurement is not a new idea in aero, of course, but it’s cool that it’s now so accessible. I’m not fully convinced of how useful but I’m very open to seeing it experimented with. It’s gadgetry at its finest. What’s not to like?

Does that answer your questions?