Diffuser Design help - Andylaurence

[andylaurence]

The side gurney is something I'd not considered. I think it'll increase frontal area though, which will increase drag. With only 185bhp, I need all the help I can get down the straights! I think venting the wheel arch to inside the sidepod will result in less drag as the inside of the sidepod should be low pressure as it shares space with the area behind the radiator. The splitter looks shorter than it is in that photo. It's about 100mm long at its shortest.

Ideally, I'd like to rebody the whole car but time and skills are in short supply! There's a lot of scope to make more of a Coke-bottle shape of the rear, move the radiator somewhere less prominent, reduce frontal area and make a decent stab at a front diffuser. One step at a time...

[miqi23]

@DRCorsa - care to show some near surface velocities on the lower side of your diffuser section?

[wesley123]

Honestly an 5mm gurney tab wouldnt add drag that much, I would even say it reduces drag since it allows extraction of air in the wheel arches.

[andylaurence]

Fair point. I do still believe that venting into the sidepod will be more efficient. Of course, that's just guessing...

[Smokes]

Before fitting a diffuser. The first question i would ask is are your lap time consistant lap after lap at race or qualifying pace. Ie each lap is within .5 of second.
Is your setup and corner weight corner weights spot on?
What condition are the tyre you are using? New or used. Are you happy with the tyre pressure cold and hot?
Is you setup and driving style getting the most out of the tyres in terms of reach ideal tyre temp and keeping the tyre heated evenly?


If none of the above are sorted out how are you going know how much a improvement a diffuser will make. As this will change the center of pressure and balance of the car completly.

[andylaurence]

@Smokes
Fair questions. I compete in Sprints, so laps are done one at a time and hours apart. Conditions generally change over that period and times do too. I've not had the car corner-weighted with me sat in it yet. Tyres are the same set from event to event as they tend to last quite well when you only do 4 laps in an event! Tyre temperature varies from stone cold on the line to anywhere between luke warm and hot enough at the finish line depending on the circuit, track temperature and length of the event. To illustrate, Castle Combe has just a few corners joined by long straights and the tyres were warm, not hot, when I returned to the pits after a lap earlier this year. Silverstone's Stowe circuit is tight and twisty with no real straights and after 1.75 laps, the tyres were nicely hot and consistently across the carcass after an event a fortnight after Castle Combe.

On a test day, I'm able to do more laps and do them a few minutes apart, so I will be able to see the difference the diffuser makes with a back-to-back test by looking at the data from the data logger. My apex speeds are usually pretty close from lap to lap and my inconsistency is from braking points not being quite right. I think I should be able to determine an improvement from that.

[wesley123]

Fair point. I do still believe that venting into the sidepod will be more efficient. Of course, that's just guessing...

By saying this, lets just think about how many teams have done that compared to other solutions.

What I called(the gurney), was utilized in many ways to allow extraction. Both in front of the wheel arch as well as aft it using its low pressure to allow extraction out of the slit(that in turn has flow out of the wheel well). I am in the opinion that an gurney provides as both an more easy fix than than letting the air flow in the sidepod as well as more efficient. Air in that area is high pressure and turbulent, which you in turn let flow into the sidepod ruining most flow there. I think that, mostly because you seem to want to redesign the whole car bit by bit an gurney is better since you are likely to change the front end in the future, rendering any work you do now as useless.

Also fences on the front splitter(take a look at the oreca for example)can be pretty useful

[andylaurence]

I should explain that inside my sidepods is nothing at all. It's just an empty box that vents at the rear to the engine compartment and has no inlet whatsoever. Most other teams vent the top of the wheel arch and various tests have shown that to be effective. I agree entirely that your idea is a good one and thank you for suggesting it. I am, as yet, unconvinced as to whether my initial idea of venting to the sidepod or your suggestion of venting externally (using a gurney or the detail you referenced on the Oreca) is better. I think there's only one way to find out and that's through testing. I can easily attach a gurney and remove the trailing edge of the wheel arch for coast-down testing. One thing that fits with the sidepod venting is the ADR factory car that was in the wind tunnel at the start of the year and the results (published in Racecar Engineering over the Summer) that showed good results from this method. It's this reason (and its utter simplicity) I like the solution more than you would expect.

I hope you don't take this post as me dismissing your ideas as it is certainly not the case. I really appreciate the time and effort you put into replying and I have learned a lot from this thread.

[wesley123]

It is good to see the research you put in it to improve your car.

As DRCosta showed in this topic I think(but cannot confirm, I am not him) He is willing to run some CFD showing what is useful and what not.

[andylaurence]

I have been working with some free software to see if I can run my own CFD simulations. Hopefully I will have something to work with shortly, but I am running out of time before the season starts. 3 months and counting!

[garygph]

Just watched your videos with great interest and have some questions that are not related to the diffuser though. So not sure they would be welcome in this thread and maybe I could PM you? They relate to driving style and also as to wether you could sit lower so as to lower your CofG etc. Have driven a similar car hence my interest.

[andylaurence]

I'm happy to answer any questions. As far as sitting lower goes, I sit on a piece of foam placed on the floor of the car, the pedals are attached to the bulkhead and my knees brush the bottom of the shock absorbers. Without major surgery (to me or the car), I can't get any lower. I'm over 6'3" tall, so I stick out the top quite some distance. I had to choose my car carefully as I don't fit in the majority of single seaters and sportscars. My driving style could be described as "scope for improvement"!

[garygph]

Without major surgery (to me or the car), I can't get any lower.

I know we all want to win but chopping ones legs off to get some time is asking a bit much!
And as for having room for improvement in the driving department just means you do not have a ridiculous ego like a lot of drivers have! Even F1 drivers always look to improving their driving style.

I was curious as to wether you need to be off the brakes and touching the throttle before entering the corner so that the car does not understeer? The sportscar I drove required this and it took some practise as I was used to trail braking into the corner. It just seemed to me that you did this into some corners and not others, although I must be honest and say it was hard to judge and I could be completely wrong.

[andylaurence]

That's one area of improvement for my driving. The car turns in nicely on the brakes as can be seen at Crystal Palace. The reason I sometimes hit the throttle on the way in is I've slowed down too much and I instinctively jump n the throttle. It's completely wrong, but it's something I'm aware of and working towards resolving. I don't get much seat time, so learning the tracks is often tricky. I did 62 minutes in total behind the wheel this year on 4 different circuits, so finding the right braking point is tricky. The nature of sprinting is that you're against the clock on your third lap. Two timed practice runs (usually 1 lap, sometimes 1.75 laps) in the morning are usually followed by two timed (again, usualy a lap) runs that count for the result in the afternoon. I'm inexperienced with both the car and the circuits as it was my first time at most of the tracks this year and I only competed in this car in one event prior to 2011. I hope to improve dramatically in 2012...

[garygph]

I was also curious as to what one can do about the airflow in the cockpit area. Seems to me to be an an area of huge drag and maybe some "gurney" type lips strategically placed could help a lot. Seeing the amount of detail you are going into elsewhere. How well seated are you laterally? Have you made a foam seat to wedge you in as it appears that you are rather loose and that does make a differance. You "feel" the car so much better when wedged in I think..could be shot down in flames by the other posters here now Lots of far more clever and experienced people here than I am!