Reducing lift on different body shape cars

[JulianEdgar]

Originally Posted by aerohead

1) the template can reliably predict separation.
2) comparison allows a visual representation of the separation-affected region.
3) Repeating myself: I don't have 'pictures', I have technical drawings.
4) Repeating myself: I have SOME technical references for SOME of the vehicles.
5) re-read 1)
I led you to water. I can't force you to drink. You don't know about templates yet. I've given you the sources. Until you explore those materials, you'll lack the proper educational foundation from which to make distinctions. It's extremely disrespectful to those who preceded you.

So this idea that "In the USA, there are dozens and dozens of modern cars with flow separation straight from the assembly line" is just based on your theories, and actually there is no evidence. OK, so now we know.

[aerohead]

Originally Posted by JulianEdgar

So this idea that "In the USA, there are dozens and dozens of modern cars with flow separation straight from the assembly line" is just based on your theories, and actually there is no evidence. OK, so now we know.

* Contemporary OEM separation is a fact for all production vehicles.
* What EcoModders would be interested in is, the degree of unnecessary separation, for a given body length, as a consequence of 'design' specification.
* 'Basic' profiles vs 'complex' profiles.
* Any grouping of vehicles of same frontal area will reveal the degree of separation as a function of drag coefficient.
* All else being equal, the vehicle with the highest top speed will possess the lowest degree of separation, the lowest drag coefficient, lowest fuel / energy consumption, highest fuel economy / range, and lowest emissions.
* The evidence is the drag coefficient, by default.

[AeroMcAeroFace]

Which template? Is it 21, 22, 22.5 or 23 degrees maximum curvature, all of which are claimed to be the "maximum" before flow separates.

The cars with roofline separation, the evidence is that they don't fit the template. The evidence for the template is that these cars have roofline separation. Circular logic?

[aerohead]

Originally Posted by AeroMcAeroFace

Which template? Is it 21, 22, 22.5 or 23 degrees maximum curvature, all of which are claimed to be the "maximum" before flow separates.

The cars with roofline separation, the evidence is that they don't fit the template. The evidence for the template is that these cars have roofline separation. Circular logic?

Great question!

1) The question would depend upon the profile.
2) I've been working with eight of them.
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3) What is 'mission critical' is that, whatever streamlined profile was chosen by the manufacturer, that that profile be maintained all the way to bodies end.
4) No 'kinks'.
5) No pressure spikes.
6) Only the moderate pressure increase that a streamlined profile will produce.
7) Otherwise, you cross the critical threshold of an already adverse pressure gradient, triggering separation.
8) The ultimate profile tangent slope angle, at any point along the aft-body, is determined by the chosen profile, and how much of it is used.
9) Really low drag bodies use ALL of it. Like the VW Flow-Body long-tail, which never exceeds 23-degrees. Cd 0.14.
10) You can't get below Cd 0.15 without the extra length.
11) And with cars designed for low drag, the length vs Cd relationship was discerned and expected trend is in fact confirmed.
12) A closer approach to the Cd 0.09-tp-Cd 0.07 of the basic bodies is only achievable through further integration of the wheels into the body.
13) The dimensional analytics can identify the original profile, and allow elongation with an extremely high confidence level that flow attachment will be maintained.
Like an electrocardiogram. A mere glance from a cardiologist will tell them if you have an irregular heartbeat. The Cartesian grid, the actual signal from your heart, plus their medical training, has ingrained the 'normal' heartbeat 'template' into their memory. It saves a lot of diagnostic time.

[JulianEdgar]

Originally Posted by aerohead

13) The dimensional analytics can identify the original profile, and allow elongation with an extremely high confidence level that flow attachment will be maintained.

Note how 'using a template' is now called 'dimensional analytics'!

It's already been demonstrated here numerous times (using photos of real cars being tuft tested) that in fact a template cannot be used to show where there will be flow attachment or separation.

To think it can is just rubbish.

[JulianEdgar]

Originally Posted by aerohead

* Contemporary OEM separation is a fact for all production vehicles.
* What EcoModders would be interested in is, the degree of unnecessary separation, for a given body length, as a consequence of 'design' specification.
* 'Basic' profiles vs 'complex' profiles.
* Any grouping of vehicles of same frontal area will reveal the degree of separation as a function of drag coefficient.
* All else being equal, the vehicle with the highest top speed will possess the lowest degree of separation, the lowest drag coefficient, lowest fuel / energy consumption, highest fuel economy / range, and lowest emissions.
* The evidence is the drag coefficient, by default.

I don't want 'default' evidence (whatever that is).

I want this evidence you promised that "In the USA, there are dozens and dozens of modern cars with flow separation straight from the assembly line" - evidence based on testing, or descriptions in technical papers, or descriptions in aerodynamic textbooks.

What you have provided so far is literally just your theory.

[aerohead]

Originally Posted by JulianEdgar

Note how 'using a template' is now called 'dimensional analytics'!

It's already been demonstrated here numerous times (using photos of real cars being tuft tested) that in fact a template cannot be used to show where there will be flow attachment or separation.

To think it can is just rubbish.

* 'Template' is easier to use than a more elaborate identifier.
* Wilson Sporting Goods Corporation, routinely employs 'template' clicking dies in the manufacture of National Football League, Regulation footballs, to ensure the Cd 0.55 ball complies with strict dimensional and weight specification requirements mandated by the officiating body.
* Templates are routinely used in thousands of commercial applications.
* It would be a great service if you'd lose the tuft argument.
* Tufts are not a reliable indicator of actual flow.
* Perhaps you'd like to select a specific vehicle for analysis?
* If you have a 'template' vehicle which has undergone laboratory testing, you may present your results.

[JulianEdgar]

Originally Posted by aerohead

* 'Template' is easier to use than a more elaborate identifier.
* Wilson Sporting Goods Corporation, routinely employs 'template' clicking dies in the manufacture of National Football League, Regulation footballs, to ensure the Cd 0.55 ball complies with strict dimensional and weight specification requirements mandated by the officiating body.
* Templates are routinely used in thousands of commercial applications.
* It would be a great service if you'd lose the tuft argument.
* Tufts are not a reliable indicator of actual flow.
* Perhaps you'd like to select a specific vehicle for analysis?
* If you have a 'template' vehicle which has undergone laboratory testing, you may present your results.

I bet they're not! Not when they so quickly show how fallacious are many of your theories! Same (apparently) with pressure testing, smoke testing, CFD plots, etc.

[AeroMcAeroFace]

A template is fine if everything fits the template, like an american football, arbitrarily suggesting that using half a template, designed for bodies of revolution is the best thing for aerodynamic analysis is not supported in any literature.
I am awaiting a paper, expert opinion or book chapter supporting the template applicability. Not anecdotally, actually supporting it, written in a book. If it is so useful it should be somewhere.

[aerohead]

Originally Posted by JulianEdgar

I don't want 'default' evidence (whatever that is).

I want this evidence you promised that "In the USA, there are dozens and dozens of modern cars with flow separation straight from the assembly line" - evidence based on testing, or descriptions in technical papers, or descriptions in aerodynamic textbooks.

What you have provided so far is literally just your theory.

That comment could be more asinine, but I don't know how.
The Drag coefficient is sufficient proof, given those of other vehicles of the same frontal area.
Testing is unnecessary.
If we have to wait for an SAE Paper for every vehicle manufactured, you're expecting something that never was, and will never be.
There seems to be extreme cognitive dissonance with respect to what engineers do.