Aerodynamic Streamlining Template: Part-C

[Piotrsko]

Didn't answer the question, side stepped it.

[freebeard]

Sonic or subsonic?

The only times I can think of where the question is pertinent would be ammunition and internal combustion head flow.

[freebeard]

Not worth a thread of it's own, for a few fleeting glimpses:

Radiator exhausts across top of hood [lower right in thumbnail]:
https://youtu.be/DjC3CslW5Vs?t=15

Full bellypan like a Colani C-Form [upper left in thumbnail]:
https://youtu.be/DjC3CslW5Vs?t=44

KNIGHT RIDER but is 1920 | Unreleased Movie Fan |

[aerohead]

Originally Posted by Piotrsko

Sonic or subsonic?

Did you get a satisfactory answer?

[Piotrsko]

Originally Posted by aerohead

Did you get a satisfactory answer?

What do you think? I think not. And suprise, there is a reason for the question if you are a fan of 12-25% thicknesses NACA airfoils of the laminar persuasion with the max thickness aft of of 40%

Has to do with boundary layers being undefined subsonic (low reynolds) but still creating a very low drag profile @ low speeds

[aerohead]

Originally Posted by Piotrsko

What do you think? I think not. And suprise, there is a reason for the question if you are a fan of 12-25% thicknesses NACA airfoils of the laminar persuasion with the max thickness aft of of 40%

Has to do with boundary layers being undefined subsonic (low reynolds) but still creating a very low drag profile @ low speeds

* Well, at least you got a 'subsonic' out of freebeard. Which was the correct answer.
* And I might have further qualified the caveats with 'sub-transonic' flow.
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* I'm not a fan of any airfoils. 'ANY.'
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* If you want to 'go there,' we can sure do that. Here, where it will all get lost, and no one will know it's here, or we can parse it out into it's own, dedicated thread, which will survive into the future, and can be referred to when anyone else brings this subject up.
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I'm presently doing a sample problem with a NACA 63,sub 4 -021, LBL, symmetrical airfoil, which is probably a 'worst-case' for a 'laminar' profile.
She's rated @ Cd min=0.006, at Rn 1,000,000, to Rn 10,000,000, based upon length, 85.86 km/h ( 53.32-mph ), standard air kinematic viscosity.
21.42% thickness, occurring at 34.28% chord, provided by Professor Schlichting, 'Boundary-Layer Theory', 7th-Edition, Figure 2.21, page 38.
* I've set the section thickness to 49.3-inches ( 1252.2mm ) in order to provide the driver and front seat passenger as much vertical interior clearance as a Toyota Prius.
* It's not looking so good so far, but I'll save the gory details until I've completely hashed it out.
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* If you wanted to select a more 'traditional,' non-symmetrical, laminar section of your liking, you could also scale it's section thickness to 49.3-inches, for easy comparison.
* At the thickness ratio of your choosing, that will fix the car's total length.
* That will allow Rn calculation at any given road velocity in calm air.
* Which will tell us what the boundary-layer is going to be like.
* The wheel placement will need to respect the 16-degree, double-10-degree, and 10-degree, SAE 'approach, breakover, and departure' angles from the roadway.
* That will fix the car's ground clearance and overall height.
* Which will also fix it's effective fineness ratio in mirror image reflection.
* Which will inform us about the lowest Cd it would be able to achieve at supercritical Reynolds number.
* Then we can compare it to other architectures.

[Piotrsko]

That is an ugly section. How are you going to keep it from pitching nose up on the highway?

Let the discussion die, pretty much no one else understood the isssue so hashing out the finer points is pretty much an effort in futility.

[freebeard]

That is an ugly section. How are you going to keep it from pitching nose up on the highway?

Not knowing what is being discussed [yet] , I can only imagine it is a Dymaxion-style bluff nose. Those were more subject to nosing into crosswinds.

Let the discussion die, pretty much no one else understood the isssue so hashing out the finer points is pretty much an effort in futility.

All-righty then. Back to first principles.

Controlling Turbulence and Evolution: How Engineers Overcome Uncertainty

5:46 And, to conserve fuel, baffles channel the air smoothly around a truck. Reynolds’s approach,

Baffles?

[aerohead]

https://ecomodder.com/forum/member-a...nes-engine.jpg

Originally Posted by Piotrsko

That is an ugly section. How are you going to keep it from pitching nose up on the highway?

Let the discussion die, pretty much no one else understood the isssue so hashing out the finer points is pretty much an effort in futility.

It's only one of many issues I flagged when doing the thought experiment.
This NACA 'Prius' ended up with:
* Height- 56.86"
* Body height- 49.3"
* Width- 70.2"
* Ground clearance- 7.56"
* Length- 230.45"
* Forebody = 34.37%-L
* Aft-body = 65.62%-L
( this is very 'ichtyoid', fishlike in proportions )
* Vergungsverhaltinisse = 3.067
* Af = approx. 25-ft-sq
* Tires are 195/ 60R17
* L/h= 4.05293
* L/h= 4.6744
* L/W= 3.28276
* Ave = 4.00336
* L/ sq-root of Af= approx. 3.84083
* Aspect ratio= 0.3046
* effective diameter ( D )= 113.72"
* effective fineness ratio= L/D= 2.0264
* theoretical minimum drag = Cd 0.0842-body only
* Cd 0.1344, with 1981 VW 'Flow-Body' wheels added
* The roofline contour is 'identical' to that of the GAC ENO. 146, at full-length, then strikes an inflexion point, at 180", then morphing into a Von Mises reflex camber, out to full length, at 230.45".
* In order to fit front and rear seat passengers, the seats had to be rotated by 5-degrees rear-slant, and dragged rearwards in order to allow below-feet, and headroom clearances.
* If this were a BEV, the skateboard would have to be mutilated, allowing shallow footwells for the four passengers, robbing torsional and buckling stiffness from the chassis.
* Allowing 40-degrees of vertical, forwards, outward vision for the driver, places straight-ahead view through a windshield glazing slant of 67-degrees, which might compromise vision due to refraction, plus interior cabin reflections onto the underside of the windshield.
* Both axles occur right at the 'potbelly' of the car.
* With standard wheels and tires, the wheelbase must be no further than 87.9", in order for the belly to strike the ground between axles, at minimum ground clearance.
* Pitching has been mentioned.
* Meeting pedestrian safety regulations might be an impossibility.
* There could be no hood/bonnet/ frunk, nor any engine or electronics access at the nose of the car.
* The ball of the SAE driver's foot is directly over the front axle.
* The steering wheels would intrude remarkably into the cabin space.
* The bodies rear 'knife- edge' would pose a life-threatening hazard to bicyclists.
* There's very little storage capacity inside the car.
* The center of gravity is higher.
* No published section data for the airfoil would be valid on account of it's aspect ratio. A completely un-known quantity ( see Abbott & Von Doenhoff / Robert T. Jones, NACA TN No. 1032, 1946.
* According to Lawrence K. Loftin, Jr., even dust adhering to a fingerprint would be enough to force the section's LBL to TBL, at any point ahead of it's engineered position of minimum pressure trigger. Chipped paint or bug-juice dried onto the leading edges increased Cd by 283%.
* At the same height, the AST-III produces Cd 0.128, before wheel fairings.
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Aerospace engineer, Matt Van Leeuwen's 'Sylph,' 3-wheeler, experienced a 2,100% drag increase compared to that of the NACA 66-Series, 6% thickness section he based the vehicle on.
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So far, I'm just not seeing any upside to laminar sections in ground proximity, Earth's turbulent boundary-layer, and 3-D flow regimes.
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PS
With such a low aspect ratio, there's little facility for dealing with edge vorticity.

[Bicycle Bob]

Sharp trailing edges don't have to be dangerous - soft material is enough to guide the air. Most bodywork could be radically lighter if it were resilient instead of stiff.