Quote:
Originally Posted by AEOLUS
What is delta Cd at first graph,why delta?
And why negative numbers?
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The graph depicts the range of change of drag to the original body design, for five (5) different aft-body lengths:
Each of the five designs indicate their representative drag 'bucket', at which Porsche's Hermann Burst referred to the 'reversal' point:
* Once the 'bucket' is reached for the specific downslope 'angle' any additional increase in downslope only 'INCREASES' drag again!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Many 'educators' fail to master this critical aspect, relating to boundary layer theory, of which Wolf H. Hucho was a student, studying under Professor Schlicting, as a graduate student. Dr. Hermann Schlicting literally 'wrote' the book on boundary layer theory!
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The delta-Cd is the measured change in drag coefficient for each of the five different rooflines, as a function of increased downslope angle.
You can see that, for a 'longer' roofline, flow can remain attached for a steeper angle, up to some 'reversal' point.
' When vehicles developed for the lowest drag coefficient are evaluated for Cd vs length, the correlation is discerned and expected trend is in fact confirmed.' W.H. Hucho