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Thanks, Aerohead & Freebeard ! Just trying to get my head around the topic what matters the most... and learning. And thanks for being patient to respond (probably basic and silly questions) but gotta start from somewhere....
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* Flow reattaches on top of the spoiler, and captures a locked-vortex against the body, as high as the spoiler.
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From drag perspective, the air flow before the spoiler what happens for the overall drag if
a) flow on front of the spoiler is attached? If flow is attached, is the spoiler directed air flow direction reducing the drag (i.e. surface pressure direction (at the end) -> without spoiler the surface pressure is against the direction of vehicle movement vs. with spoiler the surface pressure is in same direction of vehicle movement)?
b) flow on front of the spoiler is not attached -> and creates a "air bubble" (turbulent)... is this what causes overall drag increase if wake increase is not necessary the dominant factor?
According one of Hucho's document (see picture attached), if I understood correctly, regardless of attached or separated airflow, when the critical angle of rear portion of the shape is exceeded, overall drag will increase. Unfortunately, I found this information a bit too late but glad I found it.
The other attached picture is an illustration of what I am trying to understand... If Hucho's document info is correct and valid... is there a way to recover "penalty of overall drag" caused by exceeded rear slanted angle as it sounds like increased drag is evident regardless what type of flow over the rear shape one has and/or and if wake area is reduced?
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