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aerohead 12-30-2015 03:47 PM

Morelli's 'Fluid Tail'
For almost a decade now I've been using the expression 'phantom tail' to describe a degree of boat tail truncation which would not affect the drag coefficient.
In 2000,Professor Alberto Morelli,of the Torino Technical University,published 'A New Aerodynamic Approach to Advanced Automobile Basic Shapes,' in which he uses the term 'Fluid Tail.' (this SAE Paper # 2000-01-0491 was shared years ago here at ) .It's available online as a printable PDF.
*These 'fluid' tails have been investigated at least as early as 1920,with Dornier's wing research.
*Jaray/Klemperer did indirect research in the early 1920s.
*Walter Lay did indirect research in 1933.
*Kamm/Koenig-Fachsenfeld did direct research in the mid-1930s.
*3-D flow research was conducted for aircraft fuselage ball gun turrets in 1942 World War II.
*In 1963,Walter Korff illustrated the 'ring vortex'
*In 1966,Grumman appeared to utilize the fluid tail to save weight on their dorsal radar pod
*In 1976,Morelli was forced to investigate it at Pinifarina due to length restrictions with the CNR research
*In 1981,VW's Buchheim et al. indirectly measured drag in the vicinity of the fluid tail ,with the 'Flow body' long tail/truncated
In Morelli's 2000 paper,he refers to the 1984 FIAT Tipo 3 concept,with sub-Cd0.18,and 'fluid tail.'
The focus of the 2000 research is to use the fluid tail to create as low a drag as possible car,with super-truncation.
*Morelli borrows from the 'jet-pumping mechanism' penalty cited in Hoerner's section on bullet research.
*An all-forebody car body is given a ring-vortex-inducing ramp to create a controlled separation and attached transverse vortex which can insulate the bodies base from the low pressure of the inviscid flow outside the boundary layer adjacent to the separation line.
*The sloughing turbulent boundary layer and vortex stuffs the wake,so to speak,and the outer flow decelerates around this fluid tail,gaining static pressure as it moves aft.
*Since the base is insulated from the separation line,the base pressure is higher,leading to less pressure drag,and profile drag.
*Morelli's test vehicle is a FIAT Punto.You can see an oval Kamm/box-cavity with low Coanda jets which help compensate for the added wheel drag.
*The circular,or elliptical shape of the transverse separation line is crucial to the performance of the fluid tail.
PS At the time of publication in 2000,the project was still a work-in-progress,and no numbers were provided.
As of 1987,FIAT had tested a 1/2-scale 'short' car,with full cooling system,undercarriage,and features,with Cd 0.178.Considering the Cd 0.38 SMART 2 FOUR and Cd 0.31 FIAT Cinquento EV, Cd 0.178 is quite a coup!
I hope we see a follow-on paper from Professor Morelli.

MobilOne 12-30-2015 04:15 PM

This is impressive. I will have to ponder this awhile.

freebeard 12-30-2015 05:36 PM

The all-forebody car is an interesting concept. For the interior packaging.

The Punto's Kammback addition has an interesting semipermeable and perforated screen attached.

rumdog 12-30-2015 09:10 PM

Morelli paper
This is a super interesting paper aerohead. Lots of good stuff...

*centrifugal fan rims! Well of course! Then pumping the air into the wheel wake to fill in the ring. Genius.

*the shape of the vehicle shocked me a bit, but it is designed with neutralising cross winds in mind among other factors.

*underbody flow is also key to completing the ring vortex

*3 pairs of voticies coming off each wheel, wow! Go wheel skirts!

so if you did use these fan wheels on the front, where close by would you pump the flow? Behind front wheels?

I think this ends the debate of air dam vs smooth underbody.

freebeard 12-30-2015 10:06 PM

Good luck. One is a field expedient fix and the other involves reshaping the entire underbody and creating that oval truncation. ROI!

Grant-53 12-30-2015 11:44 PM

I may have to try this on the family Dodge Caravan.

MeteorGray 12-31-2015 11:46 AM

With the spermatozoon tail, I'll bet it's a handful in a strong sidewind.

freebeard 01-02-2016 02:47 AM

Weren't we looking for something that would have this effect on a rear-view mirror?

sendler 01-02-2016 05:56 AM

So a knife edge termination to a concave cavity is key in setiing up the swirl of a fluid tail.
we are already starting to see this concave treatment of the truncation on hatch backs with their "visor" following the roof line to hang over the rear glass. And the sharp termination of the side lines at the rear bumper falling away at a sharp right angle to the "step" lift over area at the rear access.

sendler 01-02-2016 08:07 AM

aero mirror
Here is a company making side view mirrors that feature an inner "oval spoiler" to create a fluid tail.
Race Mirrors: Professional Extreme - advanced aerodynamics

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