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      04-08-2018, 04:35 PM   #1
just-right
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Just-Right's Splitter and Canard Development - UPDATE 28-08-2018

I thought it would be good to share a project I have been working on. Although the Z4M is one of the best looking cars on the planet it always struck me as looking a little bit mild for an m-car. In my eyes the front especially could do with a little bit more CSL/GTS, a bit more aggression. There are several parts already on the market but the design, quality, functionality or price was something I felt was lacking. I therefore decided to design and create my own.

Last year a Stateside friend of mine who is involved with reverse engineering used photogrammetry to reconstruct his car. This involves using several hundred overlapping pictures to generate a point cloud. It took me several months to reconstruct the various external surfaces on the car.

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Having these external surfaces available in CAD allows me to perform computational fluid dynamics analysis (CFD) and assess the performance of new designs. The CFD model includes all reasonable detail such as rotating wheels/discs, moving ground, underfloor and a portion of the engine bay. The latter allows me to check the influence on radiator mass flow. The fluid volume is divided up into millions of hexahedral elements. To get the most from the simulation with the available resources it requires simplification in tight and overdetailed areas. The pictures below show the various parts/sub-assemblies and a close up of the individual mesh elements.

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The simulation matches quite well on drag in spite of some of the simplifications. It already highlights some nice avenues for front splitter and canard development. Below a picture of the pressure distribution on the surface.

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It would be great if you could share your feedback, experiences or thoughts.

---
  • Update 1 : First front diffuser iteration, page 1 post #8
  • Update 2 : Centre extension and endplate detail, page 1 post #12
  • Update 3 : First canard iteration, page 1 post #17
  • Update 4 : Canard endplate and underbody splitter length, page 1 post #18
  • Update 5 : Raised central splitter, page 1 post #20
  • Update 6 : Biplane canard, page 2 post #24
  • Update 7 : 3D scanning, page 2 post #32
  • Update 8 : Final canard design, page 2 post #35

Last edited by just-right; 08-28-2018 at 07:58 AM.
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      04-10-2018, 07:59 AM   #2
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wow, awesome work. very impressive.

Are you planning on rebuilding the whole front bumper or modifying the existing one?
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      04-10-2018, 01:14 PM   #3
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Great research so far! Many of us are already taking advantage of a front splitter setup like the one offered by APR. However, vehicle-specific and functional canards is something that is not yet available and I would personally find very interesting.
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      04-10-2018, 04:14 PM   #4
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Quote:
Originally Posted by Hammam View Post
wow, awesome work. very impressive.

Are you planning on rebuilding the whole front bumper or modifying the existing one?
Thanks Hammam! My current intent is to create designs that are additional components and leave as much of the front bumper and undertray intact. The aim is to have parts that complement the existing lines and performance. I envisage this to be more straightforward for the canards. For the splitter/front diffuser I will have to see if this is actually feasible as things progress. I see you own a Z4M Coupe, do you have any aero/bodywork modifications on your car?

Quote:
Originally Posted by Azeka1 View Post
Great research so far! Many of us are already taking advantage of a front splitter setup like the one offered by APR. However, vehicle-specific and functional canards is something that is not yet available and I would personally find very interesting.
Thanks Azeka1! Glad to hear that there are other people looking for bespoke items. I could only find universal canards available on the market. Do you run an APR splitter on your car?
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      04-10-2018, 09:08 PM   #5
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I am using universal canards with the apr splitter right now. i feel like they made a slight difference but would like to have something that's actually made for this car, ie. functions better. I also have the varis under body diffuser and a rear wing.
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      04-11-2018, 02:47 AM   #6
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Quote:
Originally Posted by just-right View Post
I see you own a Z4M Coupe, do you have any aero/bodywork modifications on your car?
had some splitters from German Tuner "Rieger Tuning" which are originally made for E90 and the Schmiedmann Carbon Lip (same as M-Stache).

Rear End: I had a FL rear bumper with OEM Aero Package Carbon Diffusor on my previous car (3.0i Roadster)

Side: I have have some OEM Aero Sideskirts with some no-name extensions. I will change them towards Carbon Extensions in summer

front: would love to have a functional and good looking lip for the Z4M Frontbumper or side splitters.
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      04-11-2018, 11:16 AM   #7
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Quote:
Originally Posted by just-right View Post
Thanks Azeka1! Glad to hear that there are other people looking for bespoke items. I could only find universal canards available on the market. Do you run an APR splitter on your car?
Yes, currently running an APR splitter on the OEM M bumper. Looking forward to seeing what you come up with.
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      04-12-2018, 04:54 PM   #8
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I knocked up a simple first draft splitter. Rather than being flat it consists of inverted aerofoil sections to increase the overall downforce versus a flat counterpart. I have added a small endplate detail on the extremity to house the vortex better at lower front ride heights.

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The front end of the car is relatively bluff and therefore air is forced up, down and sideways from the stagnation point. In the picture below it can be observed from the centreline streamlines that there is a strong downwards trajectory of the flow directly in front and above the splitter. Note that everything else in the image is coloured by pressure (red high, blue low)

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By having the aerofoil sections this flow is turned over 90 degrees and gives rise to a local acceleration and therefore pressure drop whilst maintaining fully attached. On conventional splitters with a very small radius it is not uncommon to have a separation bubble near the leading edge. It can be seen below that the whole splitter or front diffuser is yielding a pressure drop and contributing to generating downforce.

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This simple front diffuser is already yielding in the order of 9 kg of added downforce at 180 km/h. I have got several ideas to push this further and improve the aesthetics, making it more integrated and flowing with the lines of the car!
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      04-12-2018, 05:11 PM   #9
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Nice work! Thanks for this. Fantastic to see some analysis here, instead of just "winging" it. Question: your initial model looks pretty short compared to the typical spitters seen at the track. ie. This is more mstache than apr. Any thoughts on the effect of splitter length? (that is, how far it protrudes)
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      04-13-2018, 11:04 AM   #10
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Excellent work, but looking to see a much much more aggressive splitter than that.
would love to see the "Z4 Einstein (tm)" splitter through this process.
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      04-16-2018, 03:18 PM   #11
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Quote:
Originally Posted by dschultz View Post
Nice work! Thanks for this. Fantastic to see some analysis here, instead of just "winging" it. Question: your initial model looks pretty short compared to the typical spitters seen at the track. ie. This is more mstache than apr. Any thoughts on the effect of splitter length? (that is, how far it protrudes)
Thanks dschultz, thanks for your comments and indeed a very good question!

In short it is a conservative starting point. Mostly driven by ground clearance for daily driving and the aerodynamic considerations below. Now that I have a baseline to work from the overhang will undoubtedly start to creep forward though!

From a flow physics point of view it is possible to yield several times more suction than it is possible to yield pressurisation. I am trying to utilise this as much as possible by creating more of a front diffuser than a splitter. Almost the whole splitter on the first iteration is generating its downforce through this principle of accelerating the flow rather than heavily utilising the stagnation on the bumper. A benefit is that it typically doesn’t increase the drag as much.

Another aerodynamic consideration is that I don’t want the splitter centre of pressure too far forward just yet. This is to minimise the offloading of the rear axle through leverage. This will long term give us the ability to generate more downforce for the same aero balance.

Quote:
Originally Posted by Vanne View Post
Excellent work, but looking to see a much much more aggressive splitter than that.
would love to see the "Z4 Einstein (tm)" splitter through this process.
Thanks Vanne and I agree! I am sure that bit by bit – as I work through the iterations - the aggressiveness of the splitter will come towards your liking. I can see a nice list of mods on your Z4M as well
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      04-18-2018, 04:50 PM   #12
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I spend some time working on a slightly different endplate detail. Something that I though flows a bit better with the other sharper lines on the car. The endplate has a local aerofoil section to try and increase the compound expansion and get a bit more local aerodynamic load.

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I moved the centre a bit further forward which increases the splitter top surface pressurisation. Interestingly I can start to see some local propagation which is increasing the radiator mass flow. This in combination with a slight reprofiling of the sections added another 3 kg of downforce for a splitter delta of 12 kg at 180 km/h.

I am drawing everything to be higher order continuity, beyond tangency, like automotive A-class surfacing. The outboard area took a while and was a bit of a pain but what do you guys think does the endplate detail look better?
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      04-18-2018, 11:44 PM   #13
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My friend is helping me to get some canards for my car. I'm super excited with what you come up with!
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      04-18-2018, 11:55 PM   #14
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I now am working on getting fender spats with the same splitter material, but been busy.
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      04-22-2018, 03:23 PM   #15
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Quote:
Originally Posted by AriuSen View Post
My friend is helping me to get some canards for my car. I'm super excited with what you come up with!
Quote:
Originally Posted by AriuSen View Post
I now am working on getting fender spats with the same splitter material, but been busy.
Thanks for your replies AriuSen! It is nice to see that you are making some custom parts for your car. I see you are running quite a bit of aero on your car. If you don't mind me asking are you struggling with forward aero balance? In my experience fender spats can generate front downforce but come with quite a large drag increase. I have definitely seen canards outperform them. Running both is generally non-trivial due to the influence of the stagnation on the canard vortices.

I am in the process of setting up the CFD simulation for my first canard. Hopefully I can show some results over the next few days.
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      04-23-2018, 11:02 PM   #16
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Quote:
Originally Posted by just-right View Post
Quote:
Originally Posted by AriuSen View Post
My friend is helping me to get some canards for my car. I'm super excited with what you come up with!
Quote:
Originally Posted by AriuSen View Post
I now am working on getting fender spats with the same splitter material, but been busy.
Thanks for your replies AriuSen! It is nice to see that you are making some custom parts for your car. I see you are running quite a bit of aero on your car. If you don't mind me asking are you struggling with forward aero balance? In my experience fender spats can generate front downforce but come with quite a large drag increase. I have definitely seen canards outperform them. Running both is generally non-trivial due to the influence of the stagnation on the canard vortices.

I am in the process of setting up the CFD simulation for my first canard. Hopefully I can show some results over the next few days.
Awesome!! Actually I don't struggle at all with front downforce. Actually my car is really balanced right now.
Honestly the spats were intended to reduce drag and not to increase drag lol. If that's the case I need to do some more studying.

Excited to see your work too!
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      04-25-2018, 04:32 PM   #17
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I managed to run the simulation of the first draft canard. I positioned and shaped it to complement the lower line of the side ducts.

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Aerodynamically it is doing what it is supposed to. It raises the static pressure on the top surface and increases the suction underneath. This pressure difference yields the formation of a vortex which when working correctly will help manage the wheel wake. Unfortunately although aerofoil shaped, the suction on this first canard iteration is very peaky and too much on the nose of the element. The by-product is that the vortex health is suboptimal and dissipates too quickly.

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There are some good opportunities to improve the aerodynamic properties drastically by redistributing the pressure and managing the vortex strength. This will benefit the local performance and downstream influence.

What do you guys think is it getting a bit more aggressive? More to come!
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      05-09-2018, 02:52 PM   #18
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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.

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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.

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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)

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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!
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      05-10-2018, 04:58 PM   #19
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I love this stuff so much. Great work!
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      05-21-2018, 04:57 PM   #20
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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.

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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.

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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 guys like where the design is heading or not
let me know what you think!
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      05-21-2018, 05:02 PM   #21
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I love this stuff so much. Great work!
Many thanks AmmarYasirA! I enjoy sharing the process.
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      05-22-2018, 10:59 AM   #22
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Any way you could incorporate a splitter like that in the M4 GTS that you could adjust for clearance?
All whilst keeping the structural integrity of it?
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