Windshield separation bubble revealed in tuft testing (on MGA; none on Geo Metro)

[MetroMPG]

Getting back to windshield separation bubbles...

A Ford Tempo (the one Frank refers to here) can't be any worse than the 1st gen Golf/Rabbit - even it has attached flow at the windshield base, says Herr Hucho. (I should start quoting someone else - I'm wearing out the "HUCHO" keys on my computer...)

He says:

Even smoke photographs on standard production vehicles with comparatively steep windshields [see Fig. 1.2 - refers to image of the 1st gen Golf] reveal no separation at this location. The reason is that, as a rule, the junction [between hood & windshield] does not have a sharp corner but is rounded, and the windshield is curved; both of these features reduce the tendency for flow separation. (p. 160, ch 4, 4th ed)

[MetroMPG]

I'm going out to tuft test the ForkenSwift's windshield right now.

[MetroMPG]

No big surprise: according to the wool, there is no separation bubble at the base of the windshield of a 1992 Geo Metro / Swift / Firefly / Sprint / Cultus / Barina. All tufts stream back (or outward and back, closer to the sides of the glass).

Too dark to get pics, but I'll snap and post some tomorrow (maybe some video too).

That was with the wipers removed.

However with the wipers in place there IS separation - surprise, surprise - on the glass above/behind the arms & blades extending upwards for roughly 10 cm / 3-4 inches.

[Frank Lee]

Hmm. Metro has less angle at hood/windshield junction, so...

I'm surprised with the Hucho quote re: Rabbit though. Guess I'll have to get out the yarn to see what's going on once and for all with that Tempo.

[MetroMPG]

That's true.

Quick 'n' dirty Photoshop analysis says the Tempo hood angle is about 7 degrees below horizontal, vs. about 13 for the Metro.

The Tempo's windshield is raked back about 59 degrees from vertical, vs. about 61 for the Metro. (Not sure if those are the conventional references for describing those angles.)

Tuft, man, tuft!

[MetroMPG]

Pics taken at approx 40-50 km/h. (Note I was not driving down the road looking through my camera - I aimed the camera blindly, took a pile of random pics and separated the wheat from the chaff later. )

All tufts stream freely with the wipers off indicating attached flow at the windshield base and no separation bubble.

When the wipers are in place, all but one of the bottom row of tufts that are downstream of the wipers are trapped in separated flow (not surprisingly).

I also caught a few seconds of video that I'll post later.

[Southcross]

Originally Posted by MetroMPG

Getting back to windshield separation bubbles...

A Ford Tempo (the one Frank refers to here) can't be any worse than the 1st gen Golf/Rabbit - even it has attached flow at the windshield base, says Herr Hucho. (I should start quoting someone else - I'm wearing out the "HUCHO" keys on my computer...)

He says:

I'm slowly trying to learn automotive aerodynamics... are they saying that the aerodynamics of the hood-to-windshield on the Mk1 Golf/Rabbit is "good" or "bad"? by context, I'm guessing they are saying its bad?

[MetroMPG]

It's good. You want attached flow (no separation bubble / entrained vortices).

[Southcross]

Originally Posted by MetroMPG

It's good. You want attached flow (no separation bubble / entrained vortices).

very interesting... funny that my car has a "good" aerodynamic feature... and funny that my car has a lower cD than the 2010 Camaro LOL!

anwaysies.... so is that with, or without the stock windshield wipers installed?