Thought I'd overlay the drag graphs from the original car, and the one with the modified rear wheel fairing ("Test 1"):
You can see the slight reduction in drag (and lift, but not shown on this graph) that came about by removing the curvature on the top of the wheel fairing... but also the big increase in drag right at the rear....
Thanks Machin. So, theorethically, with the improved air to the rear wing (more downforce and more drag), one could reduce the angle of attack until the downforce is the same as before... (and this would result in lower than original drag).
The italiced part is just a theory of mine (as is the cleaner air to the rear wing). Would that part hold true?
It is after all the most tilted part of the wing that produces the most drag by virtue of facing backwards (which I suspect to be most important) and increasing the frontal section.
Rivals, not enemies. (Now paraphrased from A. Newey).
Sounds reasonable to me Hollus..... We do know that the biggest change so far came from sorting out the floor, so you'd think that this was still the area to spend more time playing with though.... If Ric can get another big improvement from the diffuser then he'll have an abundance of rear downforce, so a reduction in the AoA of the rear wing flap could be a nice way to get balance back and reduce overall drag further as you suggest....
Ric; So many possible things to try... so few hours in the day!
Last edited by machin on 02 Oct 2015, 08:18, edited 1 time in total.
machin wrote:
Although I must admit I've never seen diffuser strakes on a real car end half way along the diffuser... and I've never tried them in CFD myself as a result....
It does get used quite often, although I do admit it is a detailed change
LMP's use them fairly frequently, and there even was a trend of cutting out a triangle area in the strakes
ARX-02a here
The Peugeot 908 HDI FAP with a triangle cut-out in the strake.
F1 diffusers often use shorter strakes as well, some start later in the diffuser, while some end sooner etc. etc.
What I would like to know is what "feature" (pressure, velocity, Vorticity...?) on the CFD analysis would indicate that you would get a benefit from the triangular cut-out in the diffuser strake like that....?
Machin, my guess is that there's still a transverse pressure gradient at the end of the strake, and the triangular shape is studied to take advantage of that. Basically, that's a secondary vortex generator.
I'm using a similar feature in my car: if you look closely at my diffuser's strake, you'll notice a first and wider stage ending quite early, and a second, smaller one going on up the trailing edge of the diffuser. The first stage takes care of the larger and more powerful vortices that are shed from the leading edge of the diffuser; the problem with those vortices is that they don't follow very well the curvature of the diffuser itself (as well as loosing energy quickly). That's why the second stage exists, shedding much smaller, yet quite effective, vortices.
Now, a further step would be putting all of this together to form a system of vortices. That's why for the third race of the championship I've tried to make all those vortices interact constructively. It looked like a success in my private tests, but it revealed to be failure when the official results came out. Nowadays, until I'll have CFD settings sorted out, I'm using the less elegant version, the one with non interacting vortices.
BTW I could reveal some more details about how vortices used to interact under my old diffuser, if someone is interested.
Definitely, any contribution to the thread would be great.
I know it reveals some secrets but its late in the championship and well, we are learning lots together here.
Doesnt matter when, just would be good to see some info from your side. We have opened things up for others in this thread, hopefully some other teams do the same.
Latest results with diffuser strakes is interesting.
The leading edge of the diffuser blue areas are more compact compared to without strakes. Downforce has been reduced but so has drag.
