[QUOTE=JulianEdgar;626138]Just to clarify...
I have been lucky enough to have Dr Thomas Wolf, the current head of Porsche aerodynamics, reading my
Modifying the Aerodynamics of Your Road Car book.
He has been good enough to give me detailed feedback, chapter by chapter. There's a lot that he says that I'd like to add to a new edition of the book (should one happen), and a few changes I'd make based on his suggestions.
Regarding how the rear spoiler works on the early Porsche, here are the text and pics from the relevant page of the book:
Dr Wolf's comment on this page was:
"rear spoiler => perfectly explained"
It's frustrating when people take notice of those spreading theories that are quite wrong, because it wastes the time, energy and understanding of those trying to understand a really fascinating subject.[/QUOTE
Well,as soon as I clicked to respond I lost all his text, which I need for comment. I'll have to come back after making notes. Very time wasting.
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Okay, I've seen what I needed to see:
* Just as fluid mechanics predicts, it was the 'immoderate' body taper of the 911's aft-body which subjected the TBL to a pressure increase in which was impossible to support attached flow. ( Hucho page 19 )
* The 911's 'pseudo-Jaray' 'fastback' steep slope induced the vortices which induced the 'downwash' which in turn held the tufts in an orientation of the 'downwash' ( this is not, by definition, 'attached flow' ) ( Hucho page 18 )
* The presence of the spoiler lofted the rear edge of the body, up through the separated flow ( Hucho page 281 ).
* The spoiler changed the effective slope angle from, 26-degrees, to 15-degrees ( in the case of the 'whale-tail' spoiler ( I do not have a technical image of the duckbill spoiler'ed car ).
* At 15-degrees, the vortex was dead.
* The downwash was gone.
* The tufts would behave accordingly, as there was no longer the vorticity necessary to hold them against the body. So yes, in a 'contextual manner', the flow separated earlier, however the caveat is that, the flow was never 'attached' in the first place, it was only a symptom of the original vortices, now killed by the spoiler.
* The spoiler facilitated flow reattachment, not visa-versa.
* Technical writing may not have been Dr. Thomas' strong suit. Hucho's wife and former secretary helped him with his manuscript, and I've found a few errors in his text.
I was promised at Texas Tech that, none of us would ever graduate unless we could master our first language in print. I've tried very hard to properly communicate.