Multi-channel high speed pressure measurement

[freebeard]

Not saying you should care, just that you could, ....easily.

This is surmise, but at youtu.be/Q2uLwNq4jZo?t=344 in your Kamm video, at 'b' (the other 'b') we see a plan view the fore and aft portions are offset and skewed to each other, similar to the front wings on F1 cars.

I think it's analogous to a shuttlecock.

[JulianEdgar]

Originally Posted by freebeard

This is surmise, but at youtu.be/Q2uLwNq4jZo?t=344 in your Kamm video, at 'b' (the other 'b') we see a plan view the fore and aft portions are offset and skewed to each other, similar to the front wings on F1 cars.

I think it's analogous to a shuttlecock.

Yes, I've looked at the pic of the model (and the patent) but I don't understand what is achieved by that arrangement.

[JulianEdgar]

I did some testing of the pressure changes on the side of the car caused by my Edgarwit front external air curtains. Each curved curtain is an aluminum extruded aerofoil for low drag. Throttle stop testing has shown a good reduction in overall drag, and tuft testing has shown a slightly better attached airflow pattern on the side of the car.

Measured pressures without Edgarwits:



Measured pressures with Edgarwits:



The converging duct of the Edgarwits obviously causes a pressure build-up - from -110 Pa to +35 Pa in the duct. In testing I found to get the drag reduction, I needed to have the duct converging - I imagine to better squirt air across the face of the wheel. That pressure build-up also occurs ahead of the duct - from -187 up to -71 Pa.

But what is happening on the side panel behind the wheel? The figures show a marked overall increase in pressure:



You can see how consistent the percentage changes are with distance behind the wheel.

Based on the three tests I have done - throttle stop for overall drag, tuft testing for attached flow and now this pressure testing, I assume that the Edgarwits work by giving better flow attachment down the side of the car through countering the disruption caused by the front wheels.

[JulianEdgar]

When I had the Edgarwit off you could see the dust pattern left by the aerofoil. This shows very well how it is positioned:



And an overall view:

[JulianEdgar]

I've done a new video on the Edgarwits (it's a few weeks away from YouTube release).

It puts together my throttle-stop drag testing (5 per cent reduction in measured drag), tuft testing and pressure testing.

In terms of drag reduction, I think that these external air curtains are probably the best 'bang for your buck' of anything that I have tested.

I'd go for smooth wheel covers first, and then add these.

But I think that using the aerofoil extrusion for the guides is important in reducing parasitic drag (ie drag caused by the air curtain assembly itself).

Happy to help organise a shipment of the extruded aerofoil section if anyone wants it (I can't find it for sale anywhere but here in Australia). Should be able to ship internationally in multiple 1 metre lengths (group buy?). Nothing in it for me, but it's a nice thing and the local seller has always been good to deal with.

[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).

[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).

Yep, turn a knob in the cabin. I intend doing a lot of base pressure measurement, but not quite yet.

[JulianEdgar]

When I tested the Roomster before it was sold, I measured these:



Now, with more experience of the test gear, I think the -220 on the roof is not correct. Occasionally I get a glitch from one channel - perhaps a sensor blocked or something similar.

So I am now going with this:

[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.

[JulianEdgar]

Mercedes centreline pressures



Significant are:

- the relatively high pressures under the car (ie "less low") compared to the Insight and Roomster - it's not that nice underneath

- the high (again, "less low") wake pressure compared to the other two cars

- the positive pressure at the base of the rear window, showing at least partly attached flow

Looking at the pressures above and below the car, the Mercedes appears to have substantial lift – and it feels that way on the road.