[Shan2nu]

Was surfing through best motoring vids on youtube, when i came across this amazing clip of the Cyber Evo being tested.

I found the concept pretty easy to replicate and the results, even though basic compared to F1 wind tunnels, does give you a fair idea of how much drag your car faces at various wind speeds and what percentage of that drag is being utilized to create usable downforce (anyday better than blindly going in for ready-made body kits).

Check out the drag to downforce ratio difference, a well designed bumper and rear wing upgrade can make.

YouTube - VO169 - Cyber EVO @ Wind Tunnel Aero Testing Part1/2

YouTube - VO169 - Cyber EVO @ Wind Tunnel Aero Testing Part2/2

Shan2nu

[Samurai]

What do you mean why can't we have wind tunnels in India? It is in Bangalore since ages. There is a Wind Tunnel road next to ISRO campus on the old airport road. That leads to the Wind Tunnel facility of NAL.

I happened to see it in 1990 on a very rare NAL open day. They offer their Wind Tunnel facility to car makers too.

[Shan2nu]

What do you mean why can't we have wind tunnels in India? It is in Bangalore since ages. There is a Wind Tunnel road next to ISRO campus on the old airport road. That leads to the Wind Tunnel facility of NAL.

I happened to see it in 1990 on a very rare NAL open day. They offer their Wind Tunnel facility to car makers too.

I know there are wind tunnels in India, but are these open to the general public? And how much would it cost to get a car tested?

Shan2nu

[nitrogary]

quite simply for one major reason. who will pay for it?
it costs millions...
other thing about aerodynamics and drag- it increases with the square of velocity. so at 50 kmph, you are having 30-40% of resistance to motion from drag. at 90, you are having about 80-90% of resistance in drag. how often do vehicles in india go past 80 kmph?
thirdly, the way cars look is decided by the styling people predominantly. there is insufficient attention paid to aerodynamics. i have enough data to prove this.
also, it takes a lot of understanding of fluidics and fluid mechanics to actually gain significant improvements. we do not have enough experts here who can justify a wind tunnel.

[Samurai]

It is available for a hefty fee, but their testing concept is very different when I saw it 20 years back. They prefer to make smaller model and hookup hundreds of sensors in it to measure the effect of wind. The model used to cost 5L and above in 1990.

[Mpower]

Scale model testing in a small wind tunnel is very popular and very effective too. (for people who know what they are doing)

Also note that CFD tools are getting better and better everyday and Karun HRT car is full CFD..never been ina tunnel so they say.

[CPH]

You can do the same on a trailrt ot a truck for less money.

[Shan2nu]

But if you guys look at the wind tunnel in the vid, it doesn't look all that complicated.

They've just used scales under each wheel and one more to measure the force pushing the car backwards.

And the results were pretty clear. The stock body created 30kgs of darg force while causing 7kgs and 8 kgs of lift (not something you would want on a fast car).

The performance bumper and rear wing created 35kgs of drag force (5kgs extra), but the downforce increased to a whopping 32kgs at the front and 31kgs at the rear.

Having data even as basic as this might help tuners here, create absolute monsters without having to wonder how the aero mods are affecting the car.

You can do the same on a trailrt ot a truck for less money.

Not a bad idea.

Shan2nu

[wannabe loser]

Originally Posted by Mpower

Scale model testing in a small wind tunnel is very popular and very effective too. (for people who know what they are doing)

Also note that CFD tools are getting better and better everyday and Karun HRT car is full CFD..never been ina tunnel so they say.

I thought Virgin was developed completely using CFD and not HRT?

[CPH]

Originally Posted by Shan2nu

Not a bad idea.
Shan2nu

In my estimation it would be more beneficial than a wind tunnel. It is just not as practical, especially when you run out of road or when you need to go to 300kph.

But it has got one advantage over the wind tunnel. You can dial in the movements of the car on uneven surfaces. This is something the designers of the last LMP1 Mercedes didn't do properly costing the life of the driver.

[Shan2nu]

In my estimation it would be more beneficial than a wind tunnel. It is just not as practical, especially when you run out of road or when you need to go to 300kph.

Hmm, but if you test a car at say 160kmph or even 200kmph and take down the data, can't the results at 300kmph be calculated?

Like the wind tunnel in the vid. Drag force was 35kgs, front down force was 32kgs (91.4% of drag force) and rear downforce was 31kgs (88.5% of drag force).

Im sure there are formulas that can use the drag/downforce data wrt wind speed @ 200kmph and calculate how that particular setup would affect drag/downforce at 300kmph.

Only question with the trailer test is that drag and downforce depend on wind speed and not vehicle speed. A car doing 190kmph with 10kmph tail wind will actually have a wind speed of 180kmph while a car doing 190kmph with 10kmph head wind will face 200kmph of wind speed.

So we would need a sensor that can calculate the exact wind speed hitting the car, irrespective of the trailer speed.

PS : The stock body test was scary though. A total of 15kgs of lift at a wind speed of 25m/s (90kmph).

Shan2nu

[Udayrg]

@ Shan2nu but if you test a car at say 160kmph or even 200kmph and take down the data, can't the results at 300kmph be calculated?


The Drag force consists of two parts

1)Skin friction drag
2)Pressure drag

Results for drag force cannot be extrapolated for different speeds.
Because the behavior of drag force depends on different parameters.
It does not have a particular mathematical linear behavior.

There are many factors like

1)The Seperation point of the flow.

2)The wake region of the vehicle.

3)The Under hood behavior.

4) And the most important the shape (aerodynamic shape)

As a CFD eng. i would like to stress more points on as the discussions progress..


Uday

[Mpower]

Originally Posted by wannabe loser

I thought Virgin was developed completely using CFD and not HRT?

you maybe right. It was one of the new teams. Now the CFD car is beating the HRT !!!

[neel385]

Drag is a far far more complicated affair than what has been written so far. The factors affecting drag are many. Testing in a wind tunnel is a costly proposition. Apart from NAL, IIT Chennai also has a well equipped Tunnel.
As Nitrogary brought out, why test when the max speed on the road is hardly ever going to be above 90-100? Besides, CAD and other tools allow simulation of the airflow in a comp at far less costs.

[Shan2nu]

As Nitrogary brought out, why test when the max speed on the road is hardly ever going to be above 90-100?

You're not getting the point. What speed people drive at is a diff story.

You dont need to drive a car at its top speed to benefit from downforce. The test clearly showed that even at 90kmph, there was 15kgs of lift on an Evo (let alone the regular cars)

And i see so many people going in for aero mods without knowing how its affecting their car. There have even been cases where cars have crashed due to lift.

So if there was a cheaper alternative to a full fledged wind tunnel which could be made available to serious enthusiasts and tuners, it would definately make a big difference.

Jitu's car is one such example. 400whp, 1000-1200kg chassis, 0-200 in 12 secs but theres no information on the amount of drag it creates, how much of the drag is being converted into downforce or whether it is even creating any downforce at all. For all you know it might be causing the car to lift at high speeds, making it even more unstable.

Besides, CAD and other tools allow simulation of the airflow in a comp at far less costs.

Thats fine if you're designing a car from scratch but, what about those who have cars that are already in the market and want to test various body kits? Wouldn't one have to sit and recreate each and every car/body-kit that comes for an aero test?

Results for drag force cannot be extrapolated for different speeds.
Because the behavior of drag force depends on different parameters.
It does not have a particular mathematical linear behavior.

So, the only options are a wind tunnel capable of 300kmph or CFD model of the car, i guess.

Shan2nu