After some vacation reading of the book "Race car aerodynamics" I have had lots of thoughts of how to improve the car's aerodynamics, especially the lack of down force.
The common approach on this subject is that the seven is a hopeless case and don't even bother. That might be true, or could it be the other way around? Since it does have the aerodynamic properties of a brick (or worse) - even small mods can make a great difference?One problem is that you don't want to change the classic look of the seven. That is also true for a majority of seven owners. But I believed something like a flat underside could make a big difference. You can also add removable elements that you only have on the car when you're really going for it.
The question was, how much can be gained, and is it worth the effort?
Autocar did an article a long time ago (?) about wind tunnel testing of a Caterham. You can find it here:
#1 #2 #3
Some time ago I did some simple simulations of how much some downforce would affect lap time. The result was that 160N more downforce @100km/h would shorten the lap time with over a second! As a reference, F1 cars generate more than ten times of that, at the same speed. (source: the book mentioned.)
Wind tunnels are not accessible for most of us. At first I thought I would do road testing with string potentiometers measuring the suspension compression and connect it to the data logger. Straight roads are not that easy to find where I live, and going 200+ km/h on public roads are not that great either. The number of variables are endless and if something works or don't work I probably won't know why.
The book mentioned above briefly talks a bit about CFD - Computational fluid dynamics - and concludes that it is very expensive, complicated and not something for others than high end race teams. Well, time has passed since the writing of that book, and now the CFD software is not that hard to use and 30-days trials can be downloaded over the internet from many different software companies.
It turned out that the book was quite right. After experiments I now understand why top race teams still use wind tunnels. CFD simulation is very complicated, and it takes lots of effort to get accurate results. But for rough estimates it could still be very useful!
Baseline
So I made a rough simplified CAD model of my car. It may sound easy, but for a complete 3D modelling newbie it took quite a lot of time learning.
I started with high ambitions, but after a while I lowered them just to get some results at all. In these simulations the wheels are not rotating and the ground is not moving.
@160 km/h
257N front downforce
1935N drag
Note, these are rough numbers.
I use to complain about front end lift when I drive, but this is pretty much the opposite.
Anyway I plan to do some changes to the model and see how it affects the output. I also plan to investigate some individual parts in detail with finer meshes and higher accuracy.
