More drag reduction studies
 

Searching for the author of the paper Vekke posted on drag reduction for the A2, hoping to find more on the rear box fairings, I found a separate paper that expanded the reporting of the "box cavity" findings seen in the paper Vekke posted: "Base Pressure Recovery using Rear Cavity and Base Plates".

And for future reference, in case the longer list of papers paulu found are taken down, here is the "table of contents" for the site:

Session 0-1 - Mike Dickison, Programme Manager Coventry University LCVTP
An Introduction to the Low Carbon Vehicle Technology Programme.

Session 0-2 - Peter White, Professor of ThermofluidDynamics Coventry University, Chairman Automobile Division IMechE
Reducing carbon emissions does aerodynamics matter?

Session 0-3 - Chris Johnson, director, design project work coventry university
Aesthetics and aerodynamics

Session 0-4 - Trevor Haynes, Coventry University
LCVTP Workstream 12: Aerodynamics Technical Introduction

Session 0-5 - Trevor Haynes, Coventry University
Aerodynamics and Electric Vehicles

Session 1-1 - Scott Porteous, Development & Simulation Ricardo UK Ltd
LCVTP Workstream 12 - Aerodynamics Efficiency - Sensitivity Analysis of aerodynamic drag over various drive cycles

Session 1-2 - Gianluca Orso Fiet, MIRA
LCVTP Aerodynamics Process Development

Session 1-3 - Rishi Gupta, Mechanical and Automotive Engineering Dept. Coventry University
LCVTP WS 12 Aerodynamics Support Activities at Coventry University

Session 2-1 - Remus Cîrstea, Coventry University
Effect of rear body taper on a simple body

Session 2-2 - Jeff Howell, Tata Motors European Technical Centre
WS12 Aerodynamic Performance University Research Projects Base Pressure Recovery

Session 2-3 - Nick Sabrazat, MIRA
LCVTP Aerodynamics Reference car finding:Lessons learned

Session 2-4 - Adrian Gaylard, Technical Specialist Aerodynamics Jaguar Land Rover
Base Pressure Recovery using Rear Cavity and Base Plates

Session 3-1 - Jeff Howell, Tata Motors European Technical Centre
WS12 Aerodynamic Performance University Research Projects Wheel/Wheelarch Drag

Session 3-2 - Adrian Gaylard, Technical Specialist, Aerodynamics, Jaguar Land Rover Drag Reduction Through Wheel Design

Session 3-3 - Nick Sabrazat, MIRA
Wheel Arch Flow Investigation

Session 4-1 - Hussain Ali, Tata Motors European Technical Centre
Drag reduction on a production vehicle

Session 4-2 - David Plummer, Design Institute Coventry University
Aesthetic Design

Session 4-3 - Adrian Gaylard, Technical Specialist, Aerodynamics, Jaguar Land Rover

Further Opportunities
Posters
Posters 1
Posters 2

http://wwwm.coventry.ac.uk/researchn...ple%20body.pdf

This article is IMPORTANT. I recommend you save it, read it, and learn it.

This article is saying you can reduce drag 40 percent by making a tail. And the tail does not have to be very long.

And according to them, 20 degrees is about the absolute max, and even at that you are going to have problems with the bottom, but it is still worth it.

This article is worth SAVING.

Very interesting. Some of it looks like a section on tail end shapes in Hucho, but this has more images and discussion than what I recall. There are a few articles in that table of contents that should be of interest here.

Did I read correctly in thinking that 80 degree taper = 80 degree angle from the vertical tail section, or 10 degree diversion from horizontal?

I guess so, 90 degree would be level, so 80 degree would be 10 degree off from level position, that is how it seems to be when comparing pictures on that document as 70 degrees is much more steeper angle, meaning it is 20 degrees off from horizontal.

edit:
For 1.33m height, one after body would be 0.1064m long so two would be 0.2128m long, which would then need to be angled to 10 degrees angle downwards from trailing edge. That sounds horribly lot what I had in my car last summer and would explain my fuel economy gains a bit, even I did not have full height sides or bottom in there, also it means that there is lot more to be gained.

I read it as 80 degrees is 10, and 70 degrees is 20.

I also read it as 20 is probably fine for the top of the roof, and 20 works for the sides, but does not work for the bottom of the car unless ground clearance is "right".

The base cavity and base plates kinda blew my mind. I don't think Hucho addressed either so that was a great surprise. It is also interesting that they claim large gains from such short cavity lengths.

I was also totally brown away by the base plates. I would have thought that there would have so much turbulance between the body and base plate that it would have been counterproductive. Definitely some new ideas here.

What you thinking Phil?

Hucho
 

Hucho addresses this technology back in the commercial vehicle chapters.These plates are exactly what Continuum Dynamics developed at NASA Ames Research Center,Palo Alto,California decades ago.
I did one of these 'egg crate' boat tails behind my semi model and it flowed just fine.
By limiting where the air can be,and providing locked-vortices all around,the outer flow can skip over the egg crate as with Texas Tech's cab wing/half tonneau on the pickup.
They're not as good in a crosswind,but they're way out ahead of nothing,extremely light,easy to manufacture,and should cost very little.

The pick-up rear gate / partial bed cover seems a good analogue when trying to understand how these base plates work.

And when disguised as a cargorack or bikerack, or actually doing double duty as a rack, it won't draw that much attention.

( Actually, to be fair it should be mentioned that Paulu made note of the studies posted here on page 2 of the original thread - but its good to have a dedicated thread on this. )

Hey Euro, I like your thinking !
Clever idea using a bike rack disguise !

Me too.

I did note it, and linked to his post, in the OP of this thread. I was unaware of his post at first. When I saw it, I edited this post and also asked the moderators to consider merging the threads, but Metro thought there was enough difference to keep them separate. My OP was mostly interested in expanded detail on the specific drag reductions attained through the box cavity designs. That was not part of what paulu noted.

I've been thinking about this some more. Do you think a sedan owner could create a plexiglass baseplate sticking up vertically from the trunk edge, essentially creating a phantom Kammback? This would be less intrusive than making the trunk unusable but would it give meaningful drag reduction?

Link is broken. Anyone have a copy?

Looks like Coventry broke all the links, and I'm not sure how to find any papers anywhere on their site - which is sad, I haven't read them.

It looks like I had some luck searching the web for a few titles though:
http://www2.warwick.ac.uk/fac/sci/wm...baseplates.pdf
http://www2.warwick.ac.uk/fac/sci/wm...simplebody.pdf

Here is one specific to drag on electric vehicles, also covers wheel openings (and more):

http://www2.warwick.ac.uk/fac/sci/wm...tationws12.pdf

On page 10 their scale model testing shows a tiny benefit for "blanking" the wiper cavity. And their biggest benefit was with the rear diffuser.

Another point I notice in this doc is they used OpenFOAM for CFD - never heard of it, but found it here: The OpenFOAM&#174 Foundation. (I also could have found it just googling 'open source CFD,' though it's nice to know what Universities have chosen for CFD.) OpenFOAM is open source / free, looks easy (for me) to install or build for Linux *not for Windows*... but the learning curve appears very steep. Momentarily I couldn't find an answer to how you import solid objects into the OpenFOAM mesh generator, i.e. from a NURBS or Polygon file format, which is key. But I think I remember some separate open-source projects that stand alone as mesh generators, so I think there is a solution outside the scope of OpenFOAM. (Finally in order to delve into CFD one would have to consider how to setup some correlation between CFD and wind-tunnel data (preferably someone else's published wind-tunnel data), to ensure the computation is configured sensibly. Overall I'm not sure if it's worth the investment of (my) time, but it's always a temptation in the back of my mind... and now I know the name of a viable CFD suite...)

You'll find them here, amongst other stuff:

https://www.dropbox.com/sh/52o49bkru...modder_studies

Outstanding! Too bad I can only give you one Thanks for that post.
http://ecomodder.com/forum/images/bu...ost_thanks.gif
http://ecomodder.com/forum/images/bu...ost_thanks.gif
http://ecomodder.com/forum/images/bu...ost_thanks.gif

What he said.
http://ecomodder.com/forum/images/bu...ost_thanks.gif
http://ecomodder.com/forum/images/bu...ost_thanks.gif

baseplate
 

Could you do a 'back of the napkin' sketch,I'm having difficulty visualizing this.Sorry!:confused:

I honestly don't think so:

http://www-mdp.eng.cam.ac.uk/web/lib...t%20bodies.gif

Though perhaps a little depends on how high your vertical plexiglass plate rises from the trailing edge of the trunk lid?

james

Cds
 

I don't know the source of the pictorial drag table and associated Cds,but the numbers aren't in agreement with anything I've ever seen.:confused:

Oh, darn. Nevermind. That's what I get for avoiding looking things up and just trying to get relevant info quickly. Sorry. But it is true that a vertical plate will have high drag, no?

flat plate
 

Yes,next to a parachute they have about the highest drag.
Hoerner,Fachsenfeld,and Hucho(who uses Hoerner) show around Cd 1.11 for a flat plate.
'Conventional' parachutes are Cd 1.35
A 1906 Buick Model C Touring Car was measured at Cd 1.03 according to Tremulis.The highest drag ever measured for an automobile.
CAR and DRIVER's Don Sherman who did the Crisis Fighter Pinto and Z-Car found that when rear spoilers went above a 30-degree angle(from the horizon)that drag began to grow higher.
The Guerney Flap is vertical,but does not project vertically very far.Maybe an inch for the Ford Torino Talledega of 1969.

I think he is talking about these. I've seen them used in autocross to impart downforce on the rear tires, but if they are properly sized, it may create the "Phantom Kammback" effect we are seeking.

these
 

Thanks for the images.
Since the context of the photos is 'auto-crossing',then I'm presuming that the racers are trading speed for downforce (since highest attained speed in autocross is relatively low in comparison to other track racing).
Every example shown would incur a MPG penalty.Careful 'tuning' of size and angle could achieve a drag minimum at zero-yaw,but in a crosswind the benefits would be dubious.
For $2,000/hour,at Lockheed-Marietta you could find out.Eventually.

I got a tip of this saab study today:
http://publications.lib.chalmers.se/...ext/143210.pdf

Could you share this again?

Does someone have this files?
Thanks!

euromodder's latest post was in March, about the time of your first post, Mr Join Date 2009.

What are you looking for specifically? I wouldn't feel comfortable re-upping anything I have. A lot of it has been paywalled. Your best bet might be searching Ecomodder threads to see what others found of interest.

The interesting work was done at Coventry University and presented as Powerpoint slides, and by Robert Englar at Georgia State. So a search on Ecomodder on 'coventry' or 'englar' — or on the deep, dark web — might be of interest.

I'm interested in the LCVTP slides and pdfs from the first post, can you help?
Thanks

Well, I'm on a totally different system nowadays, but there's this in my albums:

http://ecomodder.com/forum/member-fr...31-1-26-08.png

The thread's about how the trail went cold, so what I did was to go to the first post and find the name Adrian Gaylard. I remember him from then, so I took that to Google. Last link on the first page of results is to some of his newer work. In the right sidebar is this:

The Effect of Base Bleed and Rear Cavities on the Drag of an SUV

Voila! Try page three. The docs I currently have saved out are available at:

http://www.vortaflow.com/consulting/...0reduction.pdf


https://www.google.com/url?sa=t&rct=...29759880,d.cGc

HTH

thanks for sharing that.

Unfornatly for me, I'm specially interested in the wheel and wheel archs flow studys... :(

What I have so far:
https://www2.warwick.ac.uk/fac/sci/w...tion120221.pdf

https://www.ara.bme.hu/oktatas/tanta...larch-drag.pdf

In that first link, task 12.3 has a later version of the screenshot I posted and is a better paper overall.

I found another folder of stuff. Try: https://www.ara.bme.hu/oktatas/tanta...larch-drag.pdf

Your link is the same as the second I posted.
I've tried to contact nick sabrazat via LinkedIn, no luck so far.

Perhaps this doesn't have my full attention. :o

PDF file names , session numbers and actual titles. ?????? Sorry I'm not more help. It's August.

Perhaps session 2-3? I can't find it via Google

No worries mate :)

As soon I have the files from Nick, I'll put them here.:thumbup:

Found a new interesting study, Wheels+covers, spats, fender skirts and stuff. Take a look:
http://publications.lib.chalmers.se/...512/250512.pdf

Thanks.

I've only gotten to 4.2. It's interesting how front wheel spats can affect the wake.