Attached flow on inclined rears, and trailing vortices

[JulianEdgar]

Originally Posted by aerohead

1) Over the past weeks there's been an underlying theme running through your correspondence.
2) If you've conducted measurements on the road with instrumentation, we are to take that as gospel.
3) If 'real' scientists, who came before you conducted tests with instrumentation, under clinical conditions, and published the results, all that is to be completely discounted.
4) Hucho's text is a compilation of results from empirical testing, conducted with laboratory-grade instrumentation, dating back to 1922.
5) My citations have to do with quotes, tables, or charts published by Hucho, Schlichting, Von Mises,Prandtl, Kamm-Fachsenfeld, Hoerner, Tamai, Abbott and Von Doenhoff, and others, whom I presume published the materials so that no individual would ever have to duplicate efforts, wasting time accomplishing redundant operations.
6) I don't know why you bought books, but I bought mine to profit from. I certainly am not in a position to replicate 98-years worth of research. The books have been a rich treasure trove of knowledge.
7) There is nothing 'theoretical' about anything I've posted. Everything was proven long ago.
8) You may be confusing 'hypothesis' for 'theory.' Only after a hypothesis is proven may it be used for theory. Students are introduced to 'theory' so they'll understand the underlying logic of formulae they may use on a day-to day basis. Like the' Theory of Gurgling Stomachs.' It's meal time, go eat something.

Your usual mix of red herrings, strawman arguments and irrelevant points.

Since they so comprehensively disprove your fallacious applications of theory, I would expect you to shortly suggest all on-road aero measurements are useless or deceptive. After all, you've already done that with tufting.

It must be a bit difficult when reality doesn't match your theories!

[aerohead]

Originally Posted by JulianEdgar

I am sorry, but that's all just so much rubbish.



Translation: the tufts show what is happening. You don't like it, so the tufts must actually be showing something else.



Translation: here is my theory, so what the tufts actually show must be wrong.



Translation: here is my theory, so what the tufts actually show must be wrong.



Translation: here is my bizarre theory of how spoilers work.



Translation: here is my even more bizarre theory, based apparently on the notion aircraft wings don't exist.



No, I know from measuring actual pressures on real cars (you could try it some time) that would definitely not be the case.



Translation: more of my bizarre theory, one not supported by textbooks from Barnard, Scibor-Rylski, et al.



Um, they vetted my book. They have already spoken!



I don't think so.



I think you've got used to quoting Hucho incorrectly, as you did above, and few people have bothered checking on the actual quotes. So far, nearly every time I have checked, it's wrong. It's a bit like someone who believes in a flat earth referencing Encyclopedia Britannica pages that mention the word 'earth'.

1) your ' ignoratio elenchi' explanation of the photograph is a logic fail.
2) you're offering a simple falsehood to explain a complicated truth.
3) the tuft orientation is actually an artifact of a phenomenon which is counterfactual to your ' folk knowledge', as Carl Sagan has referred to it.
3) I've volunteered a scientific/ fluid mechanics explanation which actually addresses the 'science' of what you're observing, however you seem to prefer to 'rule out the 'other'', 'familiarization avoidance', continued maintenance of ancient assumptions,' challenging any novel, potentially heretical position, and attempt to neutralize any opposition.
4) One of your 'theories' on how spoilers work hit the mark: ' Another way in which a rear spoiler on a sedan can reduce lift and drag is to simply promote flow reattachment.' ( page 195 of your book)
5) As to aircraft wings, I don't believe that you actually understand how they work. I offered you a number of texts which could compensate for that, however you've openly rejected all of them ,then spit in my face as an added thank you.
6) I made my living for almost six years, nationwide, measuring pressures. I have a BS in Mechanical Engineering Technology from Texas Tech University. The reason I went to college was to study fluid mechanics, and specifically road vehicle aerodynamics. And ' RACE CAR Engineering & Mechanics', by Paul Van Valkenburgh, published by the author, 1986, offers a superior method for measuring pressure profiles if you'd like to check that out.
7) I was happy to pay $ 500 / hour, and obtain actual front and rear lift data from a laboratory, normalized for local atmospheric conditions, an SAE requirement. I've had both a closed test section and open test section wind tunnel at home for decades and I know my way around with barometers,anemometers, flow hoods, smoke generators, sling-psychrometers, psychrometric charts, Pitot-tubes, Mercury- manometers, oil-filled U-Tube and Inclined manometers, and MAGNEHELICs.
7) I've no first hand knowledge of what you submitted for vetting. If your 'world renowned aerodynamicists' signed off on your theory of 'air wrapping the body', then I'd submit that they're just as ignorant of the facts as you are. I've been at this since 1974. Fundamentals don't change.
8) Pertaining to my inverted logic, with respect to Hucho's quotes. If I actually did mis-characterize something published by Hucho, how would you know that? With less education and less experience, what is it about your circumstances that would give you the intellectual high ground, and the ability to even discern the difference? I'm just curious.
9) You're free to think whatever you want, however, if we catch you going off the rails, we're going to take you to task.

[aerohead]

Originally Posted by JulianEdgar

Your usual mix of red herrings, strawman arguments and irrelevant points.

Since they so comprehensively disprove your fallacious applications of theory, I would expect you to shortly suggest all on-road aero measurements are useless or deceptive. After all, you've already done that with tufting.

It must be a bit difficult when reality doesn't match your theories!

1) Losing all expectation about everything would be my first recommendation.
2) On-road measurements are what they are. I don't have a problem with your's, although they lack scientific rigor.
3) As to tufts, you don't understand what you're looking at. It's all explained by Hucho. You have his book. I don't understand why you don't understand it. I've recommended Schlichting, Hoerner, and Bernoulli Theorem (which is online ). You'll never understand the tufts until you master this material. And that's your problem. Don't make it ours.
4) My experience is, that my observations dovetail perfectly with the theories. The real ones.

[JulianEdgar]

Originally Posted by aerohead

1)
4) My experience is, that my observations dovetail perfectly with the theories. The real ones.

I am sorry, but that's just absurd.

Tuft behaviour doesn't match with what you describe (unless one subscribes to your logical contortions - eg attached flow shown by tufts isn't really attached flow if it's caused by a downwash) and measured pressures don't match at all with what you claim occurs.

That's the issue - in the real world, your theories about what is happening simply don't stack up.

[JulianEdgar]

Originally Posted by aerohead

' RACE CAR Engineering & Mechanics', by Paul Van Valkenburgh, published by the author, 1986, offers a superior method for measuring pressure profiles if you'd like to check that out.

It's a good book - I have had it for more than 25 years. The aerodynamic pressure measuring technique described in the book is to use water manometers. So try measuring one-tenth of an inch of water with a fluid manometer in a moving car. That's about the wake pressure on the Insight at 80 km/h.

The more you write about testing, the more it's obvious that you don't have a good knowledge of it.

Why don't you look at what I have posted here, learn how to do some on-road testing - and then go and do it? That will be the quickest and easiest way for you to find out for yourself that a lot of what you post here is simply wrong.

[JulianEdgar]

Just to clarify...

I have been lucky enough to have Dr Thomas Wolf, the current head of Porsche aerodynamics, reading my Modifying the Aerodynamics of Your Road Car book.

He has been good enough to give me detailed feedback, chapter by chapter. There's a lot that he says that I'd like to add to a new edition of the book (should one happen), and a few changes I'd make based on his suggestions.

Regarding how the rear spoiler works on the early Porsche, here are the text and pics from the relevant page of the book:



Dr Wolf's comment on this page was:

"rear spoiler => perfectly explained"

It's frustrating when people take notice of those spreading theories that are quite wrong, because it wastes the time, energy and understanding of those trying to understand a really fascinating subject.

[aerohead]

Originally Posted by JulianEdgar

I am sorry, but that's just absurd.

Tuft behaviour doesn't match with what you describe (unless one subscribes to your logical contortions - eg attached flow shown by tufts isn't really attached flow if it's caused by a downwash) and measured pressures don't match at all with what you claim occurs.

That's the issue - in the real world, your theories about what is happening simply don't stack up.

* ' [P]seudo-Jaray shapes, called fastbacks... with steep-sloping rear end, produces two distinct longitudinal vortices. Due to the downwash induced by these trailing vortices, the flow along the longitudinal mid-section of the car remains attached over a long path; however ,a high vortex - induced drag is produced so that the total drag is higher than for the true Jaray shapes.'
( Page-18, Hucho )
* the behavior of the tufts is an artifact of downwash.
* the downwash is a symptom of separation-induced attached, counter-rotating, longitudinal vortices.
* the air does not 'wrap' over the camber of the 911 roofline.
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This is where your logic goes off the rails!
* In 1965, the 911's Cd 0.40 'represented an improvement' over the box-shaped bodies with drag coefficients between 0.6 and 0.8' ( Hucho,page-18)
* If the air did 'wrap' over the 911 contour, the highest pressure would exist there, not the lowest. ( Hucho page-2)
* We know this from the photograph you use of the VW XL1.
* Hucho introduces Bernoulli on page 50 and 51.
* Bernoulli's concept of 'isoenergetic' streamlines is absolutely critical to your mastery of automotive aerodynamics.
* The Bernoulli Equation is on page-51.
* Your theory of 'air wrapping' completely falls apart, upon the evidence of the Bernoulli Equation.
* Your theory is a scientific impossibility.
* I didn't create the science, I'm just a messenger. Who you'd like to kill, on account of the message.
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*Every time Hucho drops a name, the automotive aerodynamicist is tasked with learning everything they can about that person's aero contribution ( Hucho, page-1, Preface )
You appear to have utter disdain for any research done before 20-30 years ago, while Hucho admonishes you to know virtually everything you can possibly get your hands on,regardless of chronology.
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You've done so well with so many aspects of your recent book. If you can only master the fluid mechanics a bit better, there's no telling, the even greater contribution you can make.

[aerohead]

Originally Posted by JulianEdgar

It's a good book - I have had it for more than 25 years. The aerodynamic pressure measuring technique described in the book is to use water manometers. So try measuring one-tenth of an inch of water with a fluid manometer in a moving car. That's about the wake pressure on the Insight at 80 km/h.

The more you write about testing, the more it's obvious that you don't have a good knowledge of it.

Why don't you look at what I have posted here, learn how to do some on-road testing - and then go and do it? That will be the quickest and easiest way for you to find out for yourself that a lot of what you post here is simply wrong.

It's why I'd only attempt it in a wind tunnel,where everything else could be accounted for as well.
As to why don't I do it:
* I'd only do it in a lab.
* I'd have the scanivalve covering the entire length of the vehicle.
* I'd have as high a resolution ( number of taps as used by others ), perhaps 45, along with as many manometers.
* And photograph all the columns simultaneously, as other researchers have done. There could be no error as to any possible environmental variability which could adulterate the data.
* Darko is gone.
* I'd have to travel to North Carolina.
* The minimum fee would be $ 960.00 US Dollars. Plus travel expenses.
* I've already bankrupted myself doing EcoModder.
* I'd like to continue completing my house, which has languished, un-finished since 1983.
* I'd like to complete the truck-trailer project and capture the data before the thing dies of old-age ( over 400,000 miles on it ).
* Statistically, I've got around twelve years to live, and on Social Security, well below the poverty line.
PS
Another thought on the testing. We're only considering the centerline of the vehicle. We'd be 'blind' towards the edges. Since statistically, there's always a 7-mph wind blowing around the car, we also haven't covered yaw/ crosswind phenomena, which would be very hard to account for. Any temperature,barometric pressure, air density change occurring during a 'run' would have to be closely monitored and data reduced to reflect.

[aerohead]

[QUOTE=JulianEdgar;626138]Just to clarify...

I have been lucky enough to have Dr Thomas Wolf, the current head of Porsche aerodynamics, reading my Modifying the Aerodynamics of Your Road Car book.

He has been good enough to give me detailed feedback, chapter by chapter. There's a lot that he says that I'd like to add to a new edition of the book (should one happen), and a few changes I'd make based on his suggestions.

Regarding how the rear spoiler works on the early Porsche, here are the text and pics from the relevant page of the book:



Dr Wolf's comment on this page was:

"rear spoiler => perfectly explained"

It's frustrating when people take notice of those spreading theories that are quite wrong, because it wastes the time, energy and understanding of those trying to understand a really fascinating subject.[/QUOTE
Well,as soon as I clicked to respond I lost all his text, which I need for comment. I'll have to come back after making notes. Very time wasting.
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Okay, I've seen what I needed to see:
* Just as fluid mechanics predicts, it was the 'immoderate' body taper of the 911's aft-body which subjected the TBL to a pressure increase in which was impossible to support attached flow. ( Hucho page 19 )
* The 911's 'pseudo-Jaray' 'fastback' steep slope induced the vortices which induced the 'downwash' which in turn held the tufts in an orientation of the 'downwash' ( this is not, by definition, 'attached flow' ) ( Hucho page 18 )
* The presence of the spoiler lofted the rear edge of the body, up through the separated flow ( Hucho page 281 ).
* The spoiler changed the effective slope angle from, 26-degrees, to 15-degrees ( in the case of the 'whale-tail' spoiler ( I do not have a technical image of the duckbill spoiler'ed car ).
* At 15-degrees, the vortex was dead.
* The downwash was gone.
* The tufts would behave accordingly, as there was no longer the vorticity necessary to hold them against the body. So yes, in a 'contextual manner', the flow separated earlier, however the caveat is that, the flow was never 'attached' in the first place, it was only a symptom of the original vortices, now killed by the spoiler.
* The spoiler facilitated flow reattachment, not visa-versa.
* Technical writing may not have been Dr. Thomas' strong suit. Hucho's wife and former secretary helped him with his manuscript, and I've found a few errors in his text.
I was promised at Texas Tech that, none of us would ever graduate unless we could master our first language in print. I've tried very hard to properly communicate.

[freebeard]

I've tried very hard to properly communicate.

I'll vouch for that. aerohead is putting spaces after periods now.

(But you dropped a trailing ']' on your quote )

There is a lot of focus on the 911 ducktails and whaletails, but consider the Herrod Helper. A bent piece of angle metal held at a position and angle that mitigated the wake without compromising the cooling.