Porsche 911 GT3R aerodynamic drag influenced by rear wing settings

Discussion in 'Car Information and physics updates' started by robert habinak, Jan 12, 2022 at 9:55 AM.

  1. robert habinak

    robert habinak New Member

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    Hi!

    I have issue with Porsche 911 GT3R 2019 rear wing aerodynamics drag depending on wing settings.
    With rear wing max. settings top speed on Paul Ricard was 269,9 kph. Than I set up to rear wing to min. drag and top speed was 271,4 kph. So difference was only 1,5 kph. I think It should bee 10x bigger difference.


    Rear wing on Porsche 911 GT3R 2019 is one of biggest in GT3 class because of cars architekture . So rear wing setting must have big impact on car top speed.

    I have a realistic 3d model of that car.So I will make CFD simulation on this car how does rear wing setting influence aerodynamic drag. If anybody is interesting I will share my results.

    Porsche GT3 R 2019.jpg

    I will use OpenFoam for CFD calculation. Results will be aerodynamics forces (downforce, dragforce and aero ballance).I will do it for min. and max. rear wing settings.
    Then I will put those results to Bosch LapSim simulator to calculate top speed on racing track.
     
    Last edited: Jan 12, 2022 at 11:20 AM
  2. azaris

    azaris Active Member

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    Statement does not logically follow.
     
  3. Alex Hodgkinson

    Alex Hodgkinson Sector3 Developer

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    The relationship between angle of attack and total vehicle drag is not as significant as you believe. This this is quite a common misinterpretation of the wing/drag relationship. I'll explain how it really behaves.

    Let's take a look at a typical GT3 and see where the drag comes from:

    We have an overall drag coefficient of 0.74cda. How much of that comes from the wing though? I have sources which I can't disclose, but if we search the internet we can find a lot of data. APR Performance are good enough to post CFD results for each of their products. Their 250 model wing is fairly close to what's used on GT3s, so we'll look at that:

    [​IMG]

    [​IMG]

    What does that actually mean though? Luckily I've already broken it down:

    upload_2022-1-12_10-31-24.png

    The important part to focus on here is the CDA value which I've highlighted in yellow. Now remember I already established a drag coefficient of 0.74cda for a GT3. If that's on a base setting of say 10 degrees, that would mean the wing is only contributing 3% of the overall vehicle drag. At maximum angle of attack the overall drag would be 0.7583, at which the wing is still only generating 5.7% of the overall drag, and overall drag has only increased by 1%.

    Thus you can see that a rear wing on a GT car is a very small factor in total overall drag.
     
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  4. robert habinak

    robert habinak New Member

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    Thank you Alex for response.

    Porsche has much bigger wing. Its chord is 390mm and span 1900mm and it has 15mm gurney flap on it. So forces from such a big aero device must be much bigger than on APR 250 profile.

    Porsche GT3 2019-RW.jpg
    From CFD simulation for this wing alone CDA for wing is 0,140 at agle of attack 5deg in centerline and near endplates 11deg. L/D for this setting is around 10.
     
    Last edited: Jan 12, 2022 at 11:45 AM
  5. Alex Hodgkinson

    Alex Hodgkinson Sector3 Developer

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    Yes that may well be true, but even if the wing was twice the size of the APR-250 total drag increase would not be double as it's not a linear relationship. Even if it was you're only looking at single-figure drag % changes between the lowest and highest angles of attack.

    Aero data I have from GT3 teams supports this, but I'm not at liberty to share.
     
  6. Vale

    Vale Well-Known Member

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    Out of interest, which single part of the car generates most drag? Would it be tyres, front splitter then mirrors maybe?
     
  7. robert habinak

    robert habinak New Member

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    I found "real world data" for Porsche Cayman 987 by Verus engineering for comparison.
    Car features single element rear wing 1900x300mm, spront splitter with diffusers, dive plates and rear diffuser.
    So aero features of this car a more or less like GT3 cars but not as much refined.
    Verus engineering gives us aero data of their car.

    Cayman 987 Verus - drag comparison.jpg

    From that table I calculated for:

    Rear wing AoA 0 deg : CDA=0,851
    Rear wing AoA 10 deg : CDA=0,944

    and inserting in LapSim and go to test at Monza:

    Top speed comparison Monza.jpg
    Results for RW AoA 0deg - top speed is 277,0kph
    Results for RW AoA 10deg - top speed is 271,3 kph

    So you can see 5,7kph speed difference. And that car has only 300mm chord wing and with no gurney flap.
    Back straight in Paul Ricard is longer than in Monza S/F straight difference in top speed will be bigger there too.
     
    Last edited: Jan 12, 2022 at 1:54 PM
  8. Alex Hodgkinson

    Alex Hodgkinson Sector3 Developer

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    I'd question that data, cda increase per setting is much higher than I've ever seen.

    277 is not a realistic top speed for a GT4 at Monza. Just a quick google and/or watch some videos and you'll see that 265 is about the fastest any of the real cars reach.

    Also CDA/HP is higher with a GT4 car than a GT3, so any change in of the drag component will affect the speed of a GT4 more.
     
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  9. robert habinak

    robert habinak New Member

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    It is not GT4 car. It is tuned GT4 car with more aero like GT3 cars.
    Also i pluged 500hp for engine to be more like GT3 car. So actually it represents GT3 car with Cayman 987 Verus tuned car.
    From that perspective simulated top speed 277kph is in GT3 region.

    I also have old Ferrai 458 GT3 car wind tunell test from racecar engineering and will post those numbers later.
     
    Last edited: Jan 12, 2022 at 2:54 PM
  10. Alex Hodgkinson

    Alex Hodgkinson Sector3 Developer

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    Are you taking account of different rake angles at speed due to aero load and how that changes with different wing angles?
     
  11. robert habinak

    robert habinak New Member

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    Here is aero data for Ferrari 430GT3
    Wing at 0 deg, CD=0.463,CDA=0,926
    Wing at 9deg, CD=0.540,CDA=1,080
    Data come from racecar engineering july/2010
    and that include rake change .
    So delta CDA is 0,154 when comparing min. downforce setting to Max. downforce setting.
    Your Can see that delta is even bigger that on Cayman 987.
    Wing used on F430GT3 was used by Ferrari 550GT1 back in the days.
    Dimmension of wing is 2000x400.

    IMG_20220112_182306.jpg

    In my simulation i will do some test with rake change and how it will affect aero forces too.
     
    Last edited: Jan 12, 2022 at 6:19 PM
  12. robert habinak

    robert habinak New Member

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    And another example of AMR Vantage GT3 from racecar engineering magazine.
    Vantage GT3-rear wing change.jpg
    Rear wing of that car has 3 settings. Max is 16deg and min is 11,5deg (which is quite extreme). Dimmension of that wing is 2000x370mm
    They cant show absolute value only percentage of change of forces.
    So you can see that 4,5deg of rear wing change make 6,9% of total drag. If CDA of that car is 0,9 , detla CDA would be 0,062 and that with only 4,5deg of rear wing change!

    Later today my simulation of Porche will be done so I will post results. I´m testing rear wing in 3 positions - 0deg, 5deg and 8deg. So I avoid extreme settings.
     
    Last edited: Jan 14, 2022 at 10:53 AM
  13. Christian G

    Christian G Topological Agitator Beta tester

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    It differs very much depending on what type of car you're looking at.

    F.e. on a F1 car it's the rear wing (~30%), followed by the rear wheels (~20%) and front wheels (~15%) that create the most drag. But of course that's mainly due to the fact the rest of the bodywork is so streamlined it barely produces any.
     
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  14. robert habinak

    robert habinak New Member

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    So my CFD simulations are done and here are the results for Monza track:
    Car spec: 529hp, 1375kg (1295kg+80kg) based on BoP 2021 for VLN series

    Porsche rear wing AoA 7deg - baseline set up, top speed 268,3 kph
    Porsche rear wing AoA 0deg - delta CDA = - 0,116, top speed 274,6 kph, delta rake angle +0,15deg due to less force from rear wing

    911GT3R_wing0deg_vs_wing7deg_Top speed comparison Monza.jpg

    So my next simulation will be with rake change of 0,15deg (more rake angle for rear wing AoA 0deg) to see effect on top speed
     
    Last edited: Jan 14, 2022 at 9:20 AM
  15. Alex Hodgkinson

    Alex Hodgkinson Sector3 Developer

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    Interesting results. Only 2.3% change in top speed, whereas in your first post you reported a 0.6% change of top speed. It's certainly not the 5.5% change you were anticipating.