Just-Right's Splitter and Canard Development - Update 28-8-2018

[MrPT]

I remember reading that the Z4MC generates quite a lot of rear lift. The cockpit is set very far back, so the airflow doesn’t stick to the rear window very well, and there isn’t really any underbody area to use to generate aerodynamic grip unless you heavily modify the exhaust and/or extend the floor illegally. Not an issue for most of us, thankfully!

You could fit a rear gurney flap, ducktail spoiler, or GT wing.

That's what would be interesting to model - the back of the coupe drops off like a hatchback and it's hard to imagine anything other than a GT wing making much of a difference. A WRC-style wing at the top of the window might work well, but that's going to look proper fugly.

There are also rear diffusers/undergraysto smooth the flow from the rear. I think there was an OE one, a FancyWide aluminium version, and Goke/Slek/Varis carbon ones were all available at one time or another.

Ah, nice - some of them look quite serious. At least they have proper vanes instead of the "humps" you get on some aftermarket diffusers.

 

[just-right]

Sounds like a nice project beanie. Sometimes small changes can definitely have a large effect.

You are right MrPT. From the simulations I have found that the rear actually produces some lift. There is quite a bit of flow accelarating over the a and to a less extent c-pillar. The flow - although tired - is staying attached over the rear window and this increases the acceleration over the roof. The consequent pressure drop is causing a decent amount of lift over a large area. The fact that the cockpit sits a bit further rearward worsens this by being more directly above the rear axle.

The current splitter and canard design cleans up and manages some of the flow to the rear of the car and as such helps to reduce the rear lift. I will first focus on these projects but some rear items could well be on the horizon to rebalance the downforce distribution.

Keep the comments and discussions coming

 

[exdos]

Just-Right,

It's great to see your work on the aerodynamics of the Z4MC with CFD. A few years back, I did some back of a fag packet DIY undercar aero stuff on my Z4MC which, from the seat of my pants, feels as though it improves handling at higher speeds and started a thread about it here:
https://z4-forum.com/forum/viewtopi...odynamic&sid=f9271ccda9b9c1a13726f75c760c8c63

If you ever get around to doing a CFD of the underside of the car I'd be interested to learn if any of my ideas actually "work".

 

[Z4C_er]

Just-Right,

It's great to see your work on the aerodynamics of the Z4MC with CFD. A few years back, I did some back of a fag packet DIY undercar aero stuff on my Z4MC which, from the seat of my pants, feels as though it improves handling at higher speeds and started a thread about it here:
https://z4-forum.com/forum/viewtopi...odynamic&sid=f9271ccda9b9c1a13726f75c760c8c63

If you ever get around to doing a CFD of the underside of the car I'd be interested to learn if any of my ideas actually "work".

Hi Exdos, I'd love to see the pics, but they've died! Can you repost?
Oh, and nice colour Zed BTW...

 

[exdos]

Hi Exdos, I'd love to see the pics, but they've died! Can you repost?
Oh, and nice colour Zed BTW...

The photos are still on Photobucket and I find that if you use Google Chrome as your browser when using this forum, and open the link in that, you should see the thread with all illustrations.

Congratulations on the best choice of colour of your car!

 

[just-right]

Just-Right,

It's great to see your work on the aerodynamics of the Z4MC with CFD. A few years back, I did some back of a fag packet DIY undercar aero stuff on my Z4MC which, from the seat of my pants, feels as though it improves handling at higher speeds and started a thread about it here:
https://z4-forum.com/forum/viewtopi...odynamic&sid=f9271ccda9b9c1a13726f75c760c8c63

If you ever get around to doing a CFD of the underside of the car I'd be interested to learn if any of my ideas actually "work".

Back of an envelope / fag packet engineering does wonders! Like Z4C_er I can't seen any of the pictures, although I am using Google Chrome.

All of the simulations feature a full car and also incorporates the underside. I need this to model the exit conditions of the front splitter accurately.

 

[exdos]

Back of an envelope / fag packet engineering does wonders! Like Z4C_er I can't seen any of the pictures, although I am using Google Chrome.

I'm a Mac user and Safari is my browser of choice and all Photobucket photos now don't open in Safari, Firefox nor Opera but do open in Chrome on my Mac. I tested this before I posted earlier and just retested now. I can't think how to get around this for you. Photobucket is a real pig for making all photos uploaded useless as links in threads on forums :thumbsdown:

As well as fag packets, I'm a big fan of the pressure washer to demonstrate airflow in a similar manner to smoke in wind tunnels.

All of the simulations feature a full car and also incorporates the underside. I need this to model the exit conditions of the front splitter accurately.

I look forward to seeing more of your work.

 

[markplant]

I think the photobucket issue is you can see your own photos, because they are yours , if that makes any sense

 

[exdos]

I've just done a bit of searching to find a workaround to look at photos uploaded to Photobucket that do not display in threads and I've found one, which seems to work in any browser (on my Mac at least).

If you "Right Click" on the grey notice from Photobucket where an uploaded photo should be displayed in a thread, and then select "Open Link in New Tab", the selected image will then be displayed in that New Tab. It's far from an ideal solution, but at least you can look at the photos if you are interested enough in a particular thread which should be illustrated.

 

[just-right]

Finally, I managed to work a bit more on both the splitter and the canards. The aim was to make the canard more holistic with the splitter so I included a similar endplate detail and leading edge treatment. Aerodynamically, this helps to manage the vortex strength better whilst getting more local load. The canard sits a bit lower to help reduce the leading edge sensitivity due to spillage from the duct.





I have realigned the splitter endplate detail to be more flush with the hard edge of the bumper. The centre portion is longer which gives a direct load benefit. Below shown as coefficient of pressure with the blues being gradations of suction.





The new Canard is a little bit tidier by itself, utilising less energy from the flow and is maintaining a more coherent vortex structure for longer. Below is a plot of flow energy around the front tyre, red being high and anything below showcasing a loss in energy. On the non canard setup (left) the flow management around the tyre is slightly less than ideal and is cleaned up quite a bit with the canard (right)



The underbody splitter length is a very efficient way of adding downforce so a direction I will continue to follow. There are still some opportunities with the canard aerofoil sections to improve robustness. The journey continues, keep the comments coming!

 

[just-right]

If you "Right Click" on the grey notice from Photobucket where an uploaded photo should be displayed in a thread, and then select "Open Link in New Tab", the selected image will then be displayed in that New Tab. It's far from an ideal solution, but at least you can look at the photos if you are interested enough in a particular thread which should be illustrated.

Hi exdos I managed to have a look at the photos. Some quite interesting and sound ideas in my view . The big trouble is that without a flat floor or some regions that are downforce generating the aerodynamic features will have a significantly reduced effect and will break down a lot quicker. In the absence of a flat floor / diffuser managing some of the inevitable losses from existing car components will have only a small reward if any at all.

I also read that some people had questionmarks over the incidence (AoA) of your add ons. A lot of this is based on infinite wing span theory. In your case the local aspect ratio will remain attached for much longer due to the presence of the tip vortex supporting the section. It is worth noting that this vortex can yield a considerable energy loss downstream and the benefits would have to offset this.

 

[just-right]

I did a bit more work on the splitter/front diffuser. One of the things to consider is front ride height sensitivity. Although at the moment the local aerodynamic load gain versus the overall weight of the car is still rather benign it is still a good feature to try and incorporate. A nice way to achieve is to avoid a portion of the splitter bottoming out at the lowest front ride heights.







In this first iteration the central portion is raised to help towards this aim. This also allows for slightly improved flow alignment. The reduction in height of the central portion is an added aesthetic benefit in my view. In addition by incorporating a convex transition it is possible to match some of the lines of the front bumper.





At the moment the solution yields similar aerodynamic performance at the test conditions but should delay and reduce the loss in local suction at low front ride heights. Do you like where the design is heading or not, let me know what you think!

 

[MrPT]

Like it - clever idea and it might actually end up looking better than the splitters that have a flat bottom.

 

[Argenta]

I’m not sure, I always questioned that center ”gap” in height. But I realize the practical issues, and altho I’m no Porc-man I like the late 911 Turbo solution with a ”foldable” rubber spoiler. (Which inspired me to ”the rubber solution” on page 1)

 

[just-right]

Thanks for the replies MrPT and Argenta.

Unfortunately the renders (especially with the jpg compression on the forum) don't really show the details that well. The design needs more refinement both aerodynamically and aesthetically but I am happy with where it is heading.

I am currently spending a bit of time on the canards. Hopefully I will be able to update on some progress later this week.

 

[just-right]

I have done a little bit more work on the canards. I have created a bi-plane version with a smaller secondary item that sits higher. There is quite a bit less space here so I had to reduce the chord.





The design is starting to flow quite nicely with the sharp edges matching the rest of the car and the endplate detail returning on the splitter. The additional element provides extra downforce due to a local suction and pressurisation increase. It also yields a further improvement in downstream flow management by improving the energy near the bottom of the tyre and a little bit more adjacent to the wheel. The illustration below shows the flow energy distribution with no canard on the left, one canard in the middle and the bi-plane two canard setup on the right. High energy in red and low energy in blue.



Ever since I started posting here I have had a lot of interest. So first of all thanks very much for all the replies and private messages it is much appreciated. :cool!: The design of the canards are getting more and more finalised. Based on the amount of positive feedback and interest I am considering selling these to our Z4 community!

If you would be interested and haven’t already let me know could you please reply or send me a private message? If you would like to see tweaks to the design or have any recommendations then please get involved as well! The next step is to increase the size and width.

 

[Mangozac]

The canards aren't my thing aesthetically, but, depending on price of course, I would be interested in the splitter.

 

[Beedub]

im not sure you heard me the first time.... let me repeat.

Shut.... Up. and take my GOD DAMN money. :evil:

 

[just-right]

The canards aren't my thing aesthetically, but, depending on price of course, I would be interested in the splitter.

Thanks Mangozac! There is still quite a bit of aerodynamic work to be done on the splitter/front diffuser. I will keep you and others updated on the progress. The canards are the priority but nothing stopping a bit of parallel work.

im not sure you heard me the first time.... let me repeat.

Shut.... Up. and take my GOD DAMN money. :evil:

Ahahah. Cheers Beedub! Once things get up and running properly I am sure I can help you with that. :evil: Are you already rocking some aftermarket parts?

 

[Christian1000]

Looks like interesting work.

I’d be interested in hearing what Cx, CZF and CZR coefficients your base model was producing before you started the mods?

How have you modelled the cooling system/engine bay air flows and were you able to reverse engineer the cars underfloor with the same method you used for the top hat?