Wiper aero question (vertically parked)

[Christ]

It's kind of a thing I've been thinking of since both of our cars have wipers which cross over each other when parked... they sit on the windshield like this:

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Where most people's wipers sit like this:

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My question is this:

If the wipers are overlapped, when they are fully extended (wiper motor at 180* from park), they're nearly straight up and down on either side of the windshield.

Would it be aerodynamically "cleaner" to have them park in the upright position like this? (Covering them notwithstanding.) Than to have them in the OEM configuration, proverbially "in the way" of flow.

So, when parked, they would sit like this:

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On either side of the windshield.

[MetroMPG]

It's complicated by the fact that the flow near the A pillars, where the wipers would be, isn't going straight "up" the glass (parallel to the wipers); much will be crossing them at an angle, going around the A pillars onto the side glass. It's possible they could make things worse up there.

The safest place for a vertically parked wiper is in the dead center of the windshield (and even then, only when not driving in crosswind conditions, which is kind of rare).

[Frank Lee]

My educated opinion is that they'd make worse aero up there.

Yah, that's me, the only one that drives in xwinds all the time. Well I've seen the raindrops blow across the windshield, and they move up AND across, xwind or not.

Then, for the umpteenth time, I've also noticed on my car that the bottom 1/4 of the windshield is in a relatively static bubble as evidenced by the drops just sitting there.

[MetroMPG]

Frank: is there a recess ahead of your wipers/windshield? Know what I mean (like the 2009 Fit pic Ben just posted)? If not, I'd be surprised if you actually had a stagnation bubble.

[Frank Lee]

No recess.

Why do the rain drops act as if there is a dead zone on the bottom 1/4-1/3 of the windshield? That behavior DID NOT CHANGE at all when I removed the wipers + arms, and/or when I had my cowl filler on there.

[MetroMPG]

I don't know... Maybe higher pressure = lower airspeed + force of gravity on the water and they cancel each other out? OK, perhaps that's a stretch.

I just recall reading in Hucho that, absent recesses, modern cars have attached flow on their windshields. Also I'd be more inclined to draw conclusions about airflow from tufts rather than much more viscous, massive and surface tension-y water droplets.

(Sorry for hijacking your thread, Christ.)

[Frank Lee]

As you can see, Tempo windshields aren't all that laid back and the hood is pretty horizontal. I think this representation aligns with what I'm seeing with the drops:



Yeah I should yarn test it but I haven't.

[winkosmosis]

Yeah, of course air doesn't move vertically up the windshield.

[MetroMPG]

That image illustrates the flow direction at the A pillars nicely, too - addresses the original question nicely.

(Let's take the discussion of the elusive windshield separation bubble to this thread on that topic: Windshield separation bubble revealed in tuft testing (on MGA; none on Geo Metro))

[aerohead]

I would do a simple yarn and Scotch-tape tuft study to see where the air is going right now.Even though the wipers are interlaced when parked,they may be in a stagnant burble of air in front of the windshield,and not causing any measurable drag.If the air is being channeled at the sides towards the A-pillars,having them in the 180-degree position could actually hurt performance.During GM's development of their 80-mpg PNGV car,they found that the windshield wipers added zero drag.