Quote:
Originally Posted by BlackGold6.4
What is Fashenfeld tearing edge?, I assuming a tear drop edge to conform with the edge from another object. Like the edge of a truck box shape next to the body. |
Since you asked, I get to punish you with some foundational context
* Germany lost WW-I in part because they ran out of oil and rubber ( as they would also in WW-II ).
* In the runup to WW-II, Germany found out that a guy named Freiherr ( Baron ) Reinhard von Koenig-Fachsenfeld held patents on aerodynamics which might help Germany stretch strategic materials like oil.
* In exchange for the use of his patents, Germany created the FKFS, next door to Daimler-Benz ( Mercedes-Benz ) in Stuttgart,, giving Fachsenfeld free run of the place, and all its resources.
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* Koenig-Fachsenfeld is actually 'Kamm', in the context of the 'Kammback', as he held the patent for the 'K-form' roofline, something Dr. Kamm lectured about, but was not given official credit for it's birth.
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The 'tearing edge' was developed during 'Koenig's' R&D of the 'Kammback.'
* A roofline with a downslope contour/silhouette too steep to protect the boundary-layer was 'lofted' by the tearing edge, which:
1) pinched the air's pathway to the rear of the car.
2) this pinching re-constricted the streamlines.
3) since narrowly-spaced streamlines create 'faster-moving' air, the tearing edge is simply re-accelerating the flow,
4) which lowers the pressure,
5) from an adverse ( higher )pressure gradient ( responsible for flow separation ),
6) to a 'favorable ( lower ) pressure gradient' necessary for attached flow ( Dr. Thomas Wolf of Porsche refers to it as 'increasing the negative pressure gradient' ).
7) When the tearing edge reaches out to the 'reversal point,'
8) the nearest streamline re-attaches to the body, ' mending the flow' ( Goro Tamai ),
9) increasing pressure recovery [ which is the sole reason for 'aerodynamics' ( Hucho )].
10) When the air finally reaches the new 'trailing edge' of the tearing edge, and breaks away,
11) it's flowing at the slowest velocity ( Bernoulli Theorem ),
12) at the highest pressure ( Bernoulli Theorem ),
13) creating the highest base pressure in the wake ( direct measurement ),
14) which is the entire goal of 'aerodynamics.' ( Hucho ).
15) If the 'whole' tail of the car is present, there'll be 'zero' separation,
16) zero 'pressure drag',
17) only surface ( skin ) friction,
18) for lowest 'Total' drag.
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You could consider this a micro-course in boundary-layer theory, and all you would really need to know as an ecomodder. Or spend $75,000 to get you through your junior year in mechanical engineering, to learn the same thing.