Random Wind Tunnel and Smoke Pictures Thread

[aerohead]

Originally Posted by JulianEdgar

A typical Aerohead argument, where he goes up some blind alley dementedly flogging a dead horse. (There: two metaphors in one sentence, and they actually work together.)

Professional race teams also invest in huge, moving floor wind tunnels - and they're not testing trucks in them...

It's been known forever that small wind tunnels have major problems in giving accurate data - not only because of the blockage factor but also because the length of the tunnel test section influences flow behind the car.



Well that might help explain the emotional investment that some people seem to have in Aerohead's tiny tunnel testing, but unfortunately the physics doesn't actually care about how much people gave to the cause.

1) race car team activities are not germane to the mass-produced passenger vehicles, which are the focus of modification here at EcoModder.com. Don't bring them up again. Please!
2) it may be your myopic personal belief, prejudice against, and open hostility and discrimination towards 'tiny' wind tunnels which colors your comments about 'forever', however your conclusion about scientific the consensus on the topic is quite dubious at best, and overwhelmed by contradictory evidence published and available within the public domain.
Had your commentary ever reflected true insight into the scientific rigor, necessary to arrive at such conclusions as your own, it might have caught my attention, as well as that of others here at the forum.
When actually spoon-fed, scientific facts which refute your 'beliefs', facts which college students currently pay $25,000 a semester to be exposed to in an engineering curriculum, you reject the actual science, cherry-picking bits and pieces of data, while clinging to your sophomoric folk knowledge about wind tunnels, perhaps because it's the only thing which corroborates the false narrative you espouse in your book(s).
3) And if your going to comment on physics, my recommendation would be to, learn something about the topic before hand.

[aerohead]

Originally Posted by California98Civic

I had asked whether 0.25 cd was the measurement, and so I will take these two words, in context, as confirmation. 'Twas much fund crowd-funding your visit to that facility here. Thanks.

Sorry! I don't fully understand your comment. I parsed out the numbers for Spirit above at permalink # 860. Please let me know if there's something else I can share.

[freebeard]

Originally Posted by jULIANeDGAR

Well that might help explain the emotional investment that some people seem to have in Aerohead's tiny tunnel testing

You're not wrong. I drove all night long to bear witness. OTOH, Baby Template and competitive skiers are right-sized to Darko, within the limits of Reynolds number.

It's been known forever that small wind tunnels have major problems in giving accurate data - not only because of the blockage factor but also because the length of the tunnel test section influences flow behind the car.

Darko blows into a void, and was fine-tuned with mesh wall upstream of the intake.

[kach22i]

https://www.mercedes-benz.com/en/veh...-class-saloon/

The new A-Class Saloon takes advantage of the favourable conditions provided by its long rear end to undercut even the already exemplary A-Class with hatchback (Cd value from 0.25). With a benchmark of Cd = 0.22 the new saloon model even equals the original world record of the CLA Coupé. Thanks to the frontal area of 2,19 m², smaller than that of the CLA, the new A-Class Saloon has the lowest aerodynamic drag of all production vehicles worldwide.

[kach22i]

Apr 09, 2013
Slippery Slope: Production Cars Making Jaw-Dropping Aerodynamic Gains
A new trend sweeping the industry is aerodynamic vehicles that look fashionable, rather than like science projects.
https://www.wardsauto.com/technology...odynamic-gains

While not quite as slippery as the XL1, the CLA is part of a new trend sweeping the industry: Aerodynamic vehicles that look fashionable, rather than like science projects. In addition to the Mercedes, mainstream models including the Chevrolet Malibu and Toyota Avalon are sporting shockingly low Cds without looking like Sci-Fi props.

Teardrop-shaped bodies, fender skirts and other typical aero gimmicks may work miracles in the wind tunnel, but when they hit the street, consumers reject them. GM’s EV1 and first-generation Honda Insight HEV were the most aerodynamic vehicles of their day, sporting Cds of 0.19 and 0.25, respectively, more than 10 years ago. Despite innovative design and breathtaking efficiency, both flopped.

There are many reasons why the cars failed, but nerdy fender skirts and pinched hindquarters did not help...............

The CLA achieves much of its slipperiness like most new vehicles: Designers carefully manage how air streams around the car’s A-pillars and side mirrors, and how it flows through the engine compartment and around the wheels. Special underbody panels allow air to pass more freely underneath.

However, the CLA180 BlueEfficiency model achieves a world-leading 0.22 Cd with an additional list of features, including a sport chassis and suspension for a lower ride height; smaller 15-in. wheels made of a light alloy and designed to be highly aerodynamic; a radiator partially covered by a blind for active regulation of cooling air and additional belly pan and under floor treatments.

These efforts are topped off by a special rear bumper that hides the exhaust pipes and plays a significant role in lowering aerodynamic drag, a Mercedes spokesman says.............

Even so, 60% of drag still is related to the upper body of the vehicle, and tapering the roofline and rear end is on the mind of every auto maker in an effort to reduce a vehicle’s wake area. Because this can negatively impact rear-seat hip space and luggage volume, as well as aesthetics, designers are proceeding cautiously.

[Cd]

I wish they still had tufts on the cars when they do these tests.
I have seen the tuft and smoke combo tests done on the RX-7, but not much else.
When looking at the smoke on the A class, you can't even see a difference between it, and and old pickup truck.
With tufts, you really see what's going on with the airflow, all along the sides of the car.
I'd really like to know why manufacturers did away with tuft testing.
Perhaps they indeed still do tuft test, but keep the pretty smoke pictures for PR use

[kach22i]

Originally Posted by Cd

I wish they still had tufts on the cars when they do these tests.
I have seen the tuft and smoke combo tests done on the RX-7, but not much else.
When looking at the smoke on the A class, you can't even see a difference between it, and and old pickup truck.
With tufts, you really see what's going on with the airflow, all along the sides of the car.
I'd really like to know why manufacturers did away with tuft testing.
Perhaps they indeed still do tuft test, but keep the pretty smoke pictures for PR use

In one video university students were using microphones to listen to the air as it hit A-pillars, door gaps and wheel openings.

It's not just visual these days I guess.

Then you have all those micro sensors and the like.

To me smoke pictures are relaxing, like watching a babbling brook, not of lot of hard data though.

I've never seen a swirling vortex for example, the smoke seems to dissipate.

The oddest thing in the videos is that 95% of the air never goes over the roof, you have to be dead on center for the smoke not to go angling off the hood and then windscreen and roll off the A-pillars.

[freebeard]

To me smoke pictures are relaxing, like watching a babbling brook

I get the same relaxed feeling watching drone overflights of the Austin Gigafactory at 1.75x. It's like scurrying ants, except they are payloaders and dump trucks.

I've never seen a swirling vortex for example, the smoke seems to dissipate.

Try the spray swirling out of the front wheelwells of trucks on the freeway in a heavy rain.

[Cd]

After a fresh rain, I can clearly see the large vortex behind the cab on semis that are driving without their trailer.
I tried to get a video, but the contrast does not show up well.
Surely you all have seen this as well ( and the previously mentioned vortexes coming from wheelwells )
Once, I even was able to see a plastic bag that was caught in this vortex. It looks like a small tornado just behind the cab of the semi.
The airflow starts at the chassis just in front of the rear wheels and spirals upwards to the roof of the vehicle.

[aerohead]

We'd be better served if they'd lower the smoke wand enough to get into the boundary layer.
They did it for the Bionic Boxfish and one can really see the flow attachment.