Multi-channel high speed pressure measurement

[JulianEdgar]

Mercedes side and wake pressures



Significant are:

- the low pressure as the airflow wraps around onto the front bumper side panel

- the low pressure on the C pillar, perhaps indicative of a vortex here

- the fact that the wake pressure does not correspond to either the side or trunk (previous image) trailing edge pressures

[Vman455]

The underside is surprising. Does it not look like this?



(Claimed to be a W212).

[JulianEdgar]

Originally Posted by Vman455

The underside is surprising. Does it not look like this?



(Claimed to be a W212).

I've never had it on a hoist so I went and looked again. That's close - ours has only one exhaust (it's a twin turbo diesel 2.1 litre) and I don't think the middle side under trays are as wide. The front undertrays look fine but the exhaust and rear suspension are not at all smooth.

View underneath rear:

[JulianEdgar]

Go to 2:23 to see rear undercar flow (with car up on blocks):

[JulianEdgar]

Originally Posted by JulianEdgar

Three local Tesla club members have expressed interest in having their cars tested. Not sure yet of the models (although one has a roof pod, which could be fascinating) and I am also not sure how long I'll have access to each car. Ideally, I'd like to tuft and pressure test each.

I now have at least two Tesla 3 models to test in the next week.

First car - wool tuft test and pressure test - overall car

Second car - with and without these wheel covers.



I intend doing this latter test with tuft and pressure testing down the side of the car. I've also suggested to the owner taping up the openings in the covers for a third tuft/pressure test (but obviously that won't give overall drag).

Without spending a lot more time (these tests will each take 2-3 hours), any other suggestions?

[JulianEdgar]

Originally Posted by Vman455

Is your air suspension height-adjustable? After something I read just now, I'm curious if the base pressures vary at all with ride height (but, not having a height-adjustable suspension I have no way of experimenting with it myself).

Single puck in rear bumper, Magnehelic gauge, pitot static reference, 80 km/h, gusty wind at 10 km/h. Suspension height variation in round terms from lowest to highest is about 75mm. Honda Insight with undertrays, rear diffuser and rear spoiler and fins.

Standard ride height
North: -50 Pa
South: -55 Pa

Fully low
North: -45 pa
South: -50 Pa

Fully high
North: -50 Pa
South: -55 Pa

[Vman455]

Originally Posted by JulianEdgar

Fully low
North: -45 pa
South: -50 Pa

Fully high
North: -50 Pa
South: -55 Pa

Huh---exactly the opposite of what the author claimed. I wonder if I can change the ride height on my car by weighing it down and try this myself.

[JulianEdgar]

Originally Posted by Vman455

Huh---exactly the opposite of what the author claimed. I wonder if I can change the ride height on my car by weighing it down and try this myself.

Five people in car versus just the driver would be the easiest - people are heavy! But you'll also get a pitch change.

[JulianEdgar]

Tesla Model 3 with and without wheel covers. Thanks to TOCA for access to the car.





Car and Driver test of covers vs bare wheels: https://www.caranddriver.com/news/a3...ficiency-test/

[JulianEdgar]

I sent the Tesla Model 3 with / without wheel cover pics to Rob Palin, who led the aerodynamics team on the car.

He wrote:

Yes, they work really well, although we did make a little bit of an interesting aero compromise where we wanted maximum coverage of the fronts, but actually more open area on the rears. At the front we wanted to complete the turn of the air around the front corner of the car, thus minimizing the front wheel wakes.

At the rear of the car, we actually wanted to use the pull of the diffuser to draw the air back to the rear fascia surface behind the tyre, before boat-tailing a little and separating it cleanly. That was a mechanism we'd noted on Model S, where some of the more egregiously 'sporty' wheel styles hadn't had as much of an aero impact as we'd expected, due to this surprising effect at the rear.