Ultra low drag vehicles

[Piotrsko]

Ok you are not shielding from the boundary layer, you are minimizing the adverse effects. Ideally you want it driven/measured in an airconditioned building?

[aerohead]

Originally Posted by Piotrsko

Ok you are not shielding from the boundary layer, you are minimizing the adverse effects. Ideally you want it driven/measured in an airconditioned building?

A thought experiment to illustrate the race course context would be:
* The raceway is in the 'lee' of a hill ( Phoenix Int'l Raceway ).
* The hill behaves like a the cabin of a pickup truck.
* The race course is embedded within the stagnation bubble 'behind' the cabin.
* There's a Prandtl line of discontinuity created in which the race course resides, as long as the wind doesn't shift.
* Ambient conditions observed on the race course are 'dead air.'
* A small, sub-critical Reynolds number race car could get away with a 'laminar' body under this condition, as long as its velocity was held below the sub-critical Rn transition velocity. We're talking frontal areas of 3.8-sq-ft.
* No 'full-size' car, at typical travel velocities could ever get away with that.

[Piotrsko]

I see this as a moving collection of variable conditions which may or may not average out. Then there is the "laminar" body.......what part of this body is laminar and how much of the turbulent aft is going to affect data since I have yet to see any shape 100% laminar. I can see a very low drag shape getting consistent data but that is the limit, I believe. I also envision the reynolds number wandering around since race tracks have straight-a-ways to go fast on and tight turns to slow on which will affect the turbulence unless you pick a slow enough speed as to not accelerate or brake.

[aerohead]

Originally Posted by Piotrsko

I see this as a moving collection of variable conditions which may or may not average out. Then there is the "laminar" body.......what part of this body is laminar and how much of the turbulent aft is going to affect data since I have yet to see any shape 100% laminar. I can see a very low drag shape getting consistent data but that is the limit, I believe. I also envision the reynolds number wandering around since race tracks have straight-a-ways to go fast on and tight turns to slow on which will affect the turbulence unless you pick a slow enough speed as to not accelerate or brake.

Good points!
* 'laminar' is really an oxymoron.
* There's no such thing.
* What passes for 'laminar' is, a surface of laminar boundary layer, up until the flow experiences the first minimum pressure, at maximum body cross-section, then from there to the trailing edges it's all an adverse pressure gradient where it's impossible for a LBL to exist, and the transition to TBL happens immediately downstream of this maximum thickness.
* The context of 'laminar' bodies as seen at SHELL Eco Marathon, SAE, and World Solar Challenge events lies within the frontal area ( from which Reynolds number is directly associated ) and 'race' velocities, which are typically quite low. And 'calm' conditions.
* And yes, the Rn will vary with velocity. 15-mph ( burn-and- coast ) average speeds are not uncommon, and a 22-mph upper limit according to rulebook.

[freebeard]

All true except 'laminar' can't be an oxymoron.

Oxymoron - Examples and Definition of Oxymoron
https://literarydevices.net/oxymoron/
Oxymoron is a figure of speech pairing two words together that are opposing and/or contradictory. This combination of contrary or antithetical words is also known in conversation as a contradiction in terms. As a literary device, oxymoron has the effect of creating an impression, enhancing a concept, and even entertaining the reader.

[aerohead]

Originally Posted by freebeard

All true except 'laminar' can't be an oxymoron.

How about 'misnomer' ?

[Vman455]

Originally Posted by aerohead

* The context of 'laminar' bodies as seen at SHELL Eco Marathon, SAE, and World Solar Challenge events lies within the frontal area ( from which Reynolds number is directly associated ) and 'race' velocities, which are typically quite low. And 'calm' conditions.

No, this is not true! Reynolds number is directly proportional to speed and characteristic length, not area.

[aerohead]

Originally Posted by Vman455

No, this is not true! Reynolds number is directly proportional to speed and characteristic length, not area.

Characteristic 'length' for automobiles is derived from frontal area.

[JulianEdgar]

Originally Posted by aerohead

Characteristic 'length' for automobiles is derived from frontal area.

That's seriously going from the sublime to the ridiculous. It seems you're now just making stuff up - no expert, reference or paper supports this nonsense.

[freebeard]

Fineness ratio?