Flip-Up

[zac510]

But it is still a science and you should approach it in that way!

[King of Spades]

Examine the strake. It definitely directs the air upwards, on the last third of the chimney. That part would be high pressure, even though the direction was upward. In my belief, they pretty well cancel each other out as far as increasing the efficiency of chimney extraction. More than anything else, it redirects some air, which would usually directly impact on the flip-ups.

I guess you're right about the two effects cancelling as far as chimney extaction efectiveness is concerned.

Perhaps the upwash allows the hot air to be introduced into the airflow in a cleaner manner than if it weren't there, thus decreasing the drag of the chimney flow?

As you say, it's just an educated guess (as opposed to a professional guess, I suppose)... I'm merely knocking some ideas around to see if they bounce.

[manchild]

That lip on the SA would actually place a high pressure zone at the rear of the chimney, and probably hinders air extraction. It's there for downforce or aero management, not chimney extraction efficiency.

I sortof agree with Dave in that it certainly isn't for downforce - there just isn't any significant surface area to coontribute a significant percentage of downforce!
I imagine it could possibly create a vortex which subsequently may assist the extraction of air from the chimney.

[ginsu]

Examine the strake. It definitely directs the air upwards, on the last third of the chimney. That part would be high pressure, even though the direction was upward. In my belief, they pretty well cancel each other out as far as increasing the efficiency of chimney extraction. More than anything else, it redirects some air, which would usually directly impact on the flip-ups.

I guess you're right about the two effects cancelling as far as chimney extaction efectiveness is concerned.

Perhaps the upwash allows the hot air to be introduced into the airflow in a cleaner manner than if it weren't there, thus decreasing the drag of the chimney flow?

It seems to me that the upwash generated by the chimney strake would help pull hot air out of the chimney as the local velocity vectors for the airstream would be in an upward direction and the hot air would have an easier time getting out because it's in nearly the same direction.

The chimney strake could also help prevent any of the hot air from reaching the rear wing by diverting it up and over. Also, there could also be some vortex shedding on the chimney strake, most likely from the inside out, forming a CCW rotating vortex trail. The real question is whether or not the chimney strake is on the inside of the chimney as well as the outside. If it's just on the outside, then I think the vortex is really important. If it's on the inside and the outside, then I think it's there primarily for the upwash generated.

[DaveKillens]

The chimney strake could also help prevent any of the hot air from reaching the rear wing by diverting it up and over.

That sounds plausible. The strake would have less mass than extending the chimney vertically, and the drag penalty probably is about equal.