Want low drag? Don't follow a template.

[aerohead]

Originally Posted by JulianEdgar

You know, anyone reading this would think the template just dominates current aerodynamic textbooks and papers - and not that it is barely mentioned!

If you want scientific research opinions, why don't you go and read the aero textbooks for yourself? Start with the best - Aerodynamics of Road Vehicles, 5th edition, and see how much space they devote to 'optimal shapes' - two pages in 1300.

Find me some SAE engineering papers that talk about how the template - or any other similar shape - was used in the aero development of cars.

Find me a single professional aerodynamicist that uses a template when they develop cars - or even one who subscribes to the notion than any template could be used!

Seriously, you ask for research papers and yet you - and no-one else - can provide even one SAE paper that supports the notion of a template in the way it is is used in this group.

You want research papers? Go and read them. Maybe start with the couple of hundred SAE papers I read when researching my book.

You're in Germany hunting for a job - why don't you go and talk to some professional car aerodynamicists and learn some real information rather than believing rubbish on a web discussion group?

(And it's very funny that when I show in a video how absurd the template is (you know, the one in the tools section of this site, the one that is used here all the time), people then just suggest using another template!)

AERODYMAMIK DES KRAFTFAHRZEUGS, Volumes 1 & 2 is what you're after.
I guarantee that you'll be stuck in an intellectual cul de sac until you immerse yourself in it. Hucho used it. You can too!

[JulianEdgar]

Originally Posted by aerohead

If you are referring to the book, and want to use it as prima facie evidence, you'll either have to submit it, as discovery material in your brief, for your kangaroo-court, or write, in your own words, the essence of the material ( a few lines should suffice ), otherwise all I can perceive is, the actions of a coward, hiding under the skirt of a 3rd-party, pretending knowledge.
I give you chapter, verse, page numbers, and publication. I have expectations of reciprocity in a discussion among gentlemen. A term I use loosely sir.

Typical personal abuse. I gave you the references, now read them and learn.

[JulianEdgar]

Originally Posted by aerohead

I the very brief fluid mechanics literature, concerning Newtonian physics, there is no mention of Henri Coanda. A satisfactory explanation for the phenomena of a fluid following a convex profile has a fully-vetted logic and history which has no need of a 'Coanda Effect' to affect an understanding.
It's bizarre that Dr. Wolf would waste a comment on it. Although, some PhDs I know, say that it's no big thing to be a PhD. One can be completely wrong in the doctoral dissertation and still receive the degree.

Typical Aerohead snide insult to another true aerodynamic expert.

[JulianEdgar]

Originally Posted by aerohead

An aircraft application of a Coanda-esque device would be the 'blown' slots on the Japanese, Shin Meiwa PS-1 and US-1, STOL aircraft, by Kawanishi. It required only 3,060- horsepower to provide the necessary airflow volume to the wings. Stupid aeronautical engineers! All they needed was to know the illustrious Dr. Wolf and his magic technology.
Let us know how that works out on your car.

Aerohead doesn't know what Coanda Effect means when applied to road car aerodynamics, won't look at the references I have given, denigrates a professional aerodynamicist who uses the term correctly, and then goes off in his own world of irrelevant musings.

Not very helpful, to put it mildly.

[JulianEdgar]

Originally Posted by aerohead

AERODYMAMIK DES KRAFTFAHRZEUGS, Volumes 1 & 2 is what you're after.
I guarantee that you'll be stuck in an intellectual cul de sac until you immerse yourself in it. Hucho used it. You can too!

Yes, well some of us are using textbooks and SAE papers more recent than a 69 year old book.

My point remains, and no-one has (or can) address it:

If all this BS about a template were true, current aero references would cover it in great detail. After all, imagine how easy car aero would be if you could just apply a template to find out all the following:

- Show where there is separated and attached flow on existing cars
- Guide the shape of rear extensions
- Show how rear spoilers on sedans should be positioned and shaped
- Allow the assessment of the ‘aerodynamic purity’ of cars

[aerohead]

Originally Posted by AeroMcAeroFace

But doesn't the amount of stuff ahead affect the boundary layer thickness? And doesn't that make the air less "sticky" and more likely to separate?

I would think that a longer vehicle that morphs into a semicircle compared to a shorter vehicle that morphs into a semicircle, would require different rear tapers before flow detaches.

A stretch limo has the same rear profile as the car that it is based on, but will, unless I am mistaken, have different separation characteristics.

Great questions. Let's see if I can unpack them.
1) airflow at the front of a contemporary car will be 'held' in place, moving towards low pressure, essentially where the body is the thickest, and air velocity greatest ( Bernoulli Theorem [ a few key-strokes away on GOOGLE ]).
2) It's been this way since after Hucho published his drag optimization templates in 1976.
3) Aerodynamic streamlining, according to Hucho, and every other automotive aerodynamicist, has to do with reducing, or eliminating flow separation on the aft-body of the car. So it's all about the back of the car.
-------------------------------------------------------------------------------------
4) Airflow beyond the largest cross-section of the body, and moving rearwards is in the 'lee' of the wind. The air is no longer 'attacking', as it was on the forward, inclined surfaces of the forebody.
5) Due to the 'size' of cars, their boundary layer transitions from laminar, to turbulent at around 20-mph ( approx. 33 Km/h ). Which is a 'good' thing!
6) A turbulent boundary layer has the ability to survive an adverse pressure gradient ( an increasing pressure ) in the flow direction.
7) The free-stream air which lies immediately outside this turbulent boundary layer ( TBL ) has the ability to transfer kinetic energy of momentum, towards the 'wall' or, 'boundary' of the body, because air is viscous, experiences, and can transfer shearing stresses when attacked by energetic fluid near it, IF, AND ONLY IF, the shape of the body converges only slightly from location to location, creating a very subtle deceleration ramp, on which the air can slow, while rebuilding static pressure ( static regain),as it possessed before the car came along and accelerated it to higher velocity/ lower pressure ( Bernoulli ).
8) This is where 'streamlining' comes in.
9) A streamlined body has such a gentle rear contour, as to never produce a high enough pressure rise, as would require the TBL to slow ( Bernoulli ) beyond a critical threshold velocity/ pressure.
10) The air immediately adjacent to the body's surface is already 'stopped' as a consequence of viscous effects. It is what it is. Nothing can be done about it. Like gravity.
10) A contour which is not 'streamlined' will create a slowing and pressure rise ( Bernoulli ) which is of such magnitude that, for conservation of momentum to survive ( which is an immutable law of physics ), the air adjacent to the 'boundary' would have to decelerate. Which is impossible, as the air there is already 'dead.'
11) A 'too-steep' contour will bring on this conundrum, and the consequence is that the the TBL will detach from the body and attempt to flow forwards towards the lowest pressure on the car, near the 'wide' part ( near the driver's head location on the sides, and in front of the windshield header on top.
12) As the flow reverses direction, it's shearing action triggers the formation of eddies, and whirls, growing in magnitude into full-blown turbulence.
13) A loose analogy:
* consider your car's upper body as a linear camshaft profile. An air molecule traversing the length of the car over the top, as a roller-cam lifter. And the atmosphere as a weak valve spring.
14) If the cam profile is too radical, the 'spring' will be unable to maintain lifter contact with the cam 'face' as it passes under, and the valve will 'float.'
15) Same with aero. If too steep ( like a Porsche 911) the air will 'float' off it as it passes ' under.'
16) A rear spoiler can lessen the injury.
17) Re-shaping the aft-body to a streamline contour eliminates the problem altogether..

[freebeard]

11:01 Typical...
11:02 Typical...
11:06 Not very helpful...
11:11 My point remains, and no-one has (or can) address it:

Learn how to post.

11:28 I'm gonna eat lunch, and I'll continue this after.

More like this.

[JulianEdgar]

Originally Posted by freebeard

Learn how to post.

I reply to individual posts with individual posts. Of you don't like that, too bad.

More like this.

So far, the questions that were posed have been ignored!

[aerohead]

Originally Posted by AeroMcAeroFace

I think Julian and I are still waiting for the research paper showing how the template can:

- Show where there is separated and attached flow on existing cars
- Guide the shape of rear extensions
- Show how rear spoilers on sedans should be positioned and shaped
- Allow the assessment of the ‘aerodynamic purity’ of cars)

These are the claims, it is not up to us to disprove it, it up to you to prove it.

So far I have not seen, or been shown any papers, or even book chapters, that show application of a template to any car that can show the above.

It's the book, AERODYNAMIK DES KRAFTFAHZEUGS, by Fachsenfeld. I told Julien about it almost as soon as he joined us here at the Forum.

[aerohead]

Originally Posted by AeroMcAeroFace

However, Person B is cynical rather than sceptical. If Person A had showed how much heat the sun provides per square metre, showed the suns path through the sky in winter and then in summer, and also said, "it worked for me and I followed these rules, however that doesn't mean it will work for you" then that is fine.


In the UK we have houses like that, but because the sun is so low in the summer the overhangs need to be huge and are often not big enough and prolonged heat and sun has heated the houses to unbearable levels. Just because your rule of thumb works on your latitude, doesn't mean it works everywhere else.

No-one is saying following a template won't work, we are saying it is not always the best.

I don't recall ever making such a claim. 'Best' is not quantifiable. Just like 'Ultimate.' If BMW's were the 'ultimate driving machine', no one would ever part with them. There'd be know pre-owned cars for sale.
Hucho laid out what was essentially a recipe for really low drag. Hucho had used the terms 'optimum' and 'ideal' interchangeably in his 2nd-Edition.
I compiled a checklist of the criteria, and through a process of elimination the 'template' emerged.
The German Government was impressed enough with Hucho's 'template' that they had it on display in the national museum in Munich, in 1997 when I was there. I'd been impressed with it ever since I first I saw it in 1990.