A unique aero-related observation...

[SL8Brick]

In past posts, I've mentioned the addition of a 1"x1.5" rear lip spoiler to the rear hatch of my Volvo 240 wagon. Over the past several months, I've been noticing something different happening behind the car @ speeds over 45mph. While driving on rain soaked roads, there appears to be a "wall" of upward flowing water mist that seems to extend from under the rear bumper(@ ~45deg.) and disapates somewhere above the roofline. Now that Fall is upon us, I've also noticed a similar pattern with fallen leaves on the road. Prior to the installation of the spoiler, there were no noticeable flow patterns behind the car. I realize that this observation is non-scientific, but there clearly is something different happening back there.

Any thoughts??

[s1120]

Sounds like the spoiler is creating a low presure aera at the rear and "sucking" the stuff up from the bottom.

[SL8Brick]

Originally Posted by s1120

Sounds like the spoiler is creating a low presure aera at the rear and "sucking" the stuff up from the bottom.

Kinda what I was thinking as well. But is it feasible that a small spoiler could have such a dramatic effect?

[trebuchet03]

Originally Posted by SL8Brick

Kinda what I was thinking as well. But is it feasible that a small spoiler could have such a dramatic effect?

Tilt it 90 degrees (straight up) and watch what it does to your aero

Honestly, I don't know - but these interactions are rather complex (especially turbulant interactions, so much so that we "know" very little about turbulant interactions).

You could try taking it off and seeing if the same updraft is there There is a possibility that the spoiler is making you look at something you didn't pay attention to before

[SL8Brick]

Originally Posted by trebuchet03

Tilt it 90 degrees (straight up) and watch what it does to your aero

Actually, its non-adjustable. It has a gradual incline angle to 45deg.

Originally Posted by trebuchet03

Honestly, I don't know - but these interactions are rather complex (especially turbulant interactions, so much so that we "know" very little about turbulant interactions).

But aren't there general rules regarding high/low pressure zones? Eg: High pressure being drawn/attracted to low pressure areas, attemping to 'fill the void'...so to speak?

Originally Posted by trebuchet03

You could try taking it off and seeing if the same updraft is there There is a possibility that the spoiler is making you look at something you didn't pay attention to before

Like I mentioned before(...and brucepick might concur ), there were no visible flow patterns without the spoiler. I've been driving Volvo wagons for over 20yrs and I've never seen anything like this. I suppose I'm most curious to know if the altered flow induced by the spoiler is beneficial or not.

[MetroMPG]

Can you, or have you posted a pic of your spoiler?

[SL8Brick]

Originally Posted by MetroMPG

Can you, or have you posted a pic of your spoiler?

Pics are here....http://gallery.newbug.org/volvo

[MetroMPG]

Why did you choose an upwards angled spoiler? I would say it likely increases the size of the wake behind the vehicle.

[SL8Brick]

Originally Posted by MetroMPG

Why did you choose an upwards angled spoiler? I would say it likely increases the size of the wake behind the vehicle.

Believe it or not, the OE lip spoiler on some of the new Chrysler PT Cruisers was my inspiration. The Chevy Malibu Maxx SS is another "two box" with a positive downforce spoiler.
I don't doubt that my spoiler has increased the size of the wake. But it does seem to be providing 'order'(...for lack of a better word) to the airflow where outright chaos most likely existed before.
I LOVE the new C30 and I appreciate the potential benefits of the kammback design. But as brucepick had mentioned in a previous topic, it would be difficult to install a functional kammback on 240 wagon and still maintain the practicallity of the rear hatch.

[MetroMPG]

OK - so you were intentionally going for downforce, rather than reduced drag. Sorry - I misunderstood!