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 EcoModder.com ) .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.
http://i1271.photobucket.com/albums/...itled16_11.jpg
*Kamm/Koenig-Fachsenfeld did direct research in the mid-1930s.
http://i1271.photobucket.com/albums/...titled8_16.jpg
*3-D flow research was conducted for aircraft fuselage ball gun turrets in 1942 World War II.
http://i1271.photobucket.com/albums/...rohead2/-3.jpg
*In 1963,Walter Korff illustrated the 'ring vortex'
http://i1271.photobucket.com/albums/...itled21_14.jpg
*In 1966,Grumman appeared to utilize the fluid tail to save weight on their dorsal radar pod
http://i1271.photobucket.com/albums/...titled46_1.jpg
*In 1976,Morelli was forced to investigate it at Pinifarina due to length restrictions with the CNR research
http://i1271.photobucket.com/albums/...itled13_20.jpg
http://i1271.photobucket.com/albums/...itled14_19.jpg
http://i1271.photobucket.com/albums/...itled15_17.jpg
*In 1981,VW's Buchheim et al. indirectly measured drag in the vicinity of the fluid tail ,with the 'Flow body' long tail/truncated
http://i1271.photobucket.com/albums/...itled18_16.jpg
http://i1271.photobucket.com/albums/...itled19_15.jpg
In Morelli's 2000 paper,he refers to the 1984 FIAT Tipo 3 concept,with sub-Cd0.18,and 'fluid tail.'
http://i1271.photobucket.com/albums/...itled16_17.jpg
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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.
http://i1271.photobucket.com/albums/...itled12_20.jpg
*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.
http://i1271.photobucket.com/albums/...titled7_22.jpg
*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.

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

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.

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.

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

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

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

http://i1271.photobucket.com/albums/...itled12_20.jpg

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

So a knife edge termination to a concave cavity is key in setiing up the swirl of a fluid tail.
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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.
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http://www.mooncraft.jp/yuratakuya/g...prius03-04.jpg
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http://www.mooncraft.jp/yuratakuya/garage/prius/01.html
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https://upload.wikimedia.org/wikiped..._2012_0649.JPG
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http://www.blogcdn.com/www.autoblog....ius-v-live.jpg
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aero mirror
 

Here is a company making side view mirrors that feature an inner "oval spoiler" to create a fluid tail.
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Race Mirrors: Professional Extreme - advanced aerodynamics
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http://www.racemirrors.com/Picture/P...ow-viz-web.JPG
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screen
 

It would be a very good thing to see this research fleshed out with numbers provided.It's 2016,so a decade and a half have passed with no word perhaps.
Cold case.:(

front wheels
 

The front wheels probably aren't candidates for the technology, since they must articulate through their entire range of wheel-flop, as automakers refer to it.
The inner wheel face would just be too far from the inner fender wall ducting when centered, losing all available pressure to the gap.

sidewind
 

Professor Morelli's research has always taken high-speed directional stability into consideration. His 1973 patent (application 1964) included stability as a cornerstone of the design protocol.
His 'banana' car of 1978 used fin/fairings behind the rear wheels to control the center of pressure, providing for 'slip' without 'yaw.' Zero pitching moment as well.Zero lift.:)

edge/concave
 

*The important thing is that the separation line be transverse, and circular or elliptical.The Prius shown would not qualify.
The 2010 KIA Ray,PHEV concept would probably be good recent candidate.
*The concavity isn't important either.
*The ramp angle of the ring-vortex generator may be critical,although Morelli's research, as of 2000, is not mature enough to say.

race mirrors
 

Unless we get camera systems to replace our mirrors,your race mirrors are the solution. They'll be going with me to the wind tunnel in September.

Maybe the cut-out for visibility is mitigated by being within the influence of the main body.

For every optimal ramp angle there will be a corresponding step transition? Does the step have any advantage over a ramp?

Guys, what do you think about this tail that mother nature made from snow? If the timestamp doesn't work, it's at 7:00.
https://www.youtube.com/watch?v=jmAtsPiN3gw#t=7m0s

Has a similar approach to improving the rear ever been done in a wind tunnel? I mean getting a snowlike but more sticky substance and let it shape itself on the rear.

Spray-on foam and a sandblaster instead of a smoke wand? Maybe you could spray the foam wet and left it solidify in the wake.

I suspect the reason the picture that appears on the laptop in the 40 minute video shows so much symmetry is that the car is down in a street grid that channelizes the air so there is no gusting, and the car is parked nose into the wind.

http://ecomodder.com/forum/showthrea...ure-11745.html

cut-out/ step
 

*You'll have to help me with what you mean by 'cut-out.'
*As far as ramp vs step,we'll have to wait for a follow-on report from Morelli.He provides no specific information in the 2000 paper.

snow tail
 

They're all fun to look at,and I suspect that many would generate some interesting drag coefficients.
Ice has been used in a wind tunnel in an attempt to let the moving air sculpt it into a low drag form,but there were erosion problems.
If you tried to use snow in a tunnel,the leading edges of the drive fan would have to be remote,and protected from anything but air touching them.

He's talking about the mirror which has a cut out in the step to allow the pathway for vision.
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This mirror is an example of what I am talking about regarding a concave area to set up the swirl. Even though Morelli doesn't specify a concave form, I think we would agree his research on this concept is incomplete. I would intuitively suggest that a concave form with a knife edged break leading to a quarter round inner wall/ base joint feature would be the most efficient shape in order to set up the rolling toroidal air formation needed for the root of the fluid tail. With a concave depth approaching half the narrow width of the outer oval.
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The inner round over might not make much difference but the concave depression seams obvious to me. I would love to see some comparative coast down data on the Prius with the concave truncated tail that was posted above. Even though it followed the body and was not perfectly oval, it looks like it would be very effective even though the swirl would not approach the ideal toroid motion because of the corners.

mirror
 

Okay,thanks!
Yes,the clear plastic portion is a box-cavity,which is capturing a locked-vortex,which the outer flow skips over like Morelli's fluid tail.
The length,and inset dimension of the cavity respect the ideal pathway.The 'cut-out' is just a practical consideration.
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The Prius extension is a box cavity as well,with a transverse separation line which gets equal pressure basically all around which is better for a higher base pressure and overall lower drag.
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It does lack Morelli's requirement for the transom geometry necessary for the fluid tail.If you look at the Fiat Punto mods,the roof extension appears to be softening the edge radii between the attachment point and trailing edge,rolling it and morphing into a more elliptical cross section.I did this with the CRX best I could.
http://i1271.photobucket.com/albums/...ead2/205-1.jpg

What sendler said. I checked for a third page before I hit Submit for this:

Instead of the traverse cut it has a notch, which I presume is for the driver's sight-line. But the mirror is under the influence of a larger body, which might mitigate the sub-optimal form.

I thought there were wind tunnels that could add snow. Maybe they have heated leading edges.

The lower corners of that elliptical form are the hard part. Morelli resorted to pumped air from hubcaps, since he didn't have a flat-four air pump in the lower rear.

larger body/snow/lower corners
 

*Yes,in virtually all the tunnel photos we can see that the airflow in the mirror region is skewed,including my video from DARKO.There is a distance from the body at which the interference drag minimum of the mirror is optimized.If we don't get approval for camera systems,we may see more basic research into lower drag mirror systems.In the meantime,I'll be watching 24-hours of LeMans, LMP-1,race car technology.These teams do everything for a reason.
*In climatic wind tunnels,the turning vanes can be heated or cooled to maintain a constant air density during testing.(the air mover itself will inadvertently heat the airstream ).Freeze-testing is done in a climatic chamber I believe,separate from the wind tunnel.Eglin Air Force Base,Florida, has a chamber large enough to freeze a 747.
To allow snowflakes to impact the fan blades,at the velocities they run at could be devastating to the leading edges,as well as ruin the dynamic balance of the blades,potentially catastrophic.
*Yeah,if Morelli had the air-cooled boxer engine,he could have ducted the cooling air off the cylinders/heads' sheetmetal to help create the Coanda nozzles.:)He said they were losing 2/3rds of the air from the wheel turbines due to gap leakage.:o

2010 KIA Ray concept
 

here's a peek at Kia's transom,compared to Morelli's first 'fluid-tailed' CNR of 1978
http://i1271.photobucket.com/albums/...titled1_33.jpg
http://i1271.photobucket.com/albums/...ntitled285.jpg

I'm still pondering Morelli's design with pick-up modifications in mind.

This appears to be a trend in some new car designs, check out the yet to come out LR Discovery, sporting some very obvious rear aero tweaks

http://imgd1.aeplcdn.com/600x337/cw/...59233.jpg?wm=0

2010 KIA Ray concept

It looks like someone's been doing their homework. :thumbup:

cptsideways -- It's hard to see anything through the dazzle camo, but you've opened a door:

http://o.aolcdn.com/hss/storage/mida...015AU01219.jpg
http://www.autoblog.com/2016/01/05/vw-budd-e-concept-ces-official/

The electric 'microbus' VW showed at CES. Capsule review: It looks like a BMW i3 got humped by some Ford. The seating layout, headrest/seat belt, the slide-out running board under the side door, the slide out trunk — all good, but the curved window line and solar panels means it will never have slot windows and a sunroof.

Anyone who has soldiered uphill, in the dark and rain, in an old microbus will be dismayed by the blue strip lighting in the grille and the mid-air hand gestures to open the doors. It does have a little shelf under the dashboard, but it won't hold anything, it's just decorative.

Back on-topic: I wonder if the aerodynamics would be better with that base plate extended or retracted. :)

pickup mods
 

Don't do what I did with the T-100 bedcover for sure.I'll have to redo all the sides,rolling in from the rail top,instead of the Jaray 'combination'-type plan-taper above the rails.

base plate
 

The base plate must be an entire fraction of the transom area,and must be at zero yaw to have a chance.
With the partial base plate,at zero yaw,if there were reattachment and vortex capture,there'd be a pressure conflict between the original wake remnant,and the smaller new wake,causing vortex-induce drag.:(

additional cross-sections
 

Here are a few additional rear-view cross-sections for early research vehicles which happen to 'fit' Morelli's criteria for body cross-sections favorable to the fluid tail,if truncated.
This is the Lange Car,which influenced Ferdinand Porsche's first sports cars,starting,1939
http://i1271.photobucket.com/albums/...titled5_26.jpg
Here is the Schl'o'rwagen,pillbug car
http://i1271.photobucket.com/albums/...titled2_32.jpg

An excellent observation.

Examples of EcoModder fluid tails
 

Here are a few tails constructed by EcoModder members which easily qualify for Morelli,fluid tail architecture:
JethroBodine
http://i1271.photobucket.com/albums/...titled5_27.jpg
HydroJim
http://i1271.photobucket.com/albums/...titled3_31.jpg
redneck
http://i1271.photobucket.com/albums/...titled2_34.jpg
and our fearless leader,MetroMPG
http://i1271.photobucket.com/albums/...titled4_29.jpg