Quote:
Originally Posted by JulianEdgar
And now I have tested on a day with gusting 25-30 km/h crosswinds. And, in those conditions, the Edgarwits do absolutely nothing to reduce drag. The throttle-stop speeds with and without the aerofoils is identical.
So that behoves the question: do any air curtains work in gusty crosswinds? I have never seen any published research on this, so I have asked an expert I know. It will be interesting to see what he says.
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The expert got back to me (he is head of aero at a major car company and had already given me feedback on the throttle-stop drag testing method).
I first asked him if the window up / window down results I was getting in different wind conditions were reasonable. He said:
Your window-opening results look plausible to me (not that there’s much data around).
I then asked him about the Edgarwits air curtains not appearing to work in crosswinds. He said:
I like your “air curtain”. I’d call it a turning vane, as it’s external. Looks similar in concept at least to something I experimented with a while back. I think your results are about right for that kind of system. It’s always going to be a challenge at yaw as you’ll get separation off the leading edge of the vane. I’d think it should be good to 5 degrees or so. The interesting thing here is given environmental conditions/vehicle operation profile is it a benefit or detriment? Only a long-term evaluation could really say.
Our internally ducted (behind the front fender) air curtains tend to do better at yaw than straight-ahead.
He went on:
With these kinds of intervention, the benefit always depends on the place you start from: the better the front corner design and its integration with the wheel arch, the less scope for benefit.
A device through or over which the flow passes always has a local drag of its own (device drag). It’s key to minimise that. With your vane arrangement it might be worth looking at whether the internal channel should expand (diffusing), contract or remain constant. A diffusing flow will give the lowest device drag due to pressure recovery. A contracting channel will accelerate the flow and give more downstream effect. The question is: where does the best balance lie?
On the gusty element: vehicle aerodynamics as practised is overwhelmingly (/disappointingly) about performance at zero yaw in low-turbulence flow. The only OEM I know that use “gusty” onset flow conditions for drag development is [redacted]. They do this through their CFD models. The heavy truck industry tend to do a bit better (because they have to) in this regard and use at least an approximation to the wind-averaged drag (a function of range of static yaw angles).
And he was nice enough to finish off:
Anyway, interesting work and results that make sense.