Following up on my first Monza F1 CFD Article, this article goes more in depth about Angle of Attack and Drag reduction for Race Cars.
Every year, those of us that follow the Technology in Formula One are particularly interested in a few certain races. Monaco is one end of the spectrum, where teams abandon attempts at Drag reduction and focus on maximum Downforce. On the other end of the spectrum, we have Monza. Here, teams don't necessarily want to reduce Downforce, but they absolutely must reduce Drag in order to be competitive.
Most likely, if you are reading this, you have already seen the updates by Scarbs, Somers, F1Technical, and others. What I want to talk about is the Engineering behind those decisions, which tend to involve reducing the Angle of Attack of the wing, reduced Chord, and possibly reduced Airfoil Camber (not sure if this was implemented by teams, but it will be covered here regardless).
Though we are mainly concerned with Drag my Aerodynamic Coefficients - Lift Article may be helpful.
Here are some Airfoil Resources.
To understand what's going on, one thing you need to know is the Drag Polar. Since an F1 car operates in the Incompressible regime, the equation for the Drag Polar is simplified.
The Coefficient of Drag is the Zero Lift Drag, plus the Drag due to Lift (Induced Drag). You can see that the Coefficient of Lift has a big effect on the Drag. High Angles of Attack increase the Coefficient of Lift, which increases the Induced Drag and slows the F1 Race Car down at high speed which means a low lap time around Monza.
What are the other terms? AR is the Aspect Ratio, which is the Wingspan divided by the Chord. That is why you see teams reduce the Chord of their wings, it increases the Aspect Ratio, which Decreases the Induced Drag portion of the Drag Polar. In fact reducing the Chord will also reduce the Zero Lift Drag since the F1 Car has less bodywork in the air.
Last is e. That is the Span Efficiency (AKA Oswald Efficiency). To get a perfect Span Efficiency you need an Elliptical Wing, such as on a Spitfire. Another example was the P-47. This is beyond the scope of this writing, since to my immediate knowledge I don't know of this terms use in F1.
So now we see how the Drag Polar is described in an equation. Lets see if the Theory holds up to our quick CFD Analysis on these F1 Rear Wings.
For the Analysis I took a simple NACA 2412 at 10 Degrees Angle of Attack to symbolize a Formula One Race Car Rear Wing. What I did is ran CFD on that, a NACA 2412 at 0 Angle of Attack, a highly cambered NACA 9412 at 0 Angle of Attack, and a NACA 2412 at 0 Angle of Attack with a longer Chord. This should show the simple trends involved without me having to do a few days worth of CFD crunching to write this CFD Article.
NACA 2412 10 Degree Angle of Attack
NACA 2412 0 Degree Angle of Attack
Note the strength of the Vortex for the F1 Wing at its "standard" Angle of Attack. When reducing the Angle of Attack, the Vortex Strength is significantly Diminished. What is happening is the Coefficient of Lift is being reduced. This reduced the Induced Drag portion of the Drag Polar on the Race Car.
NACA 2412 10 Degrees Angle of Attack [A]
NACA 2412 0 Degrees Angle of Attack [B]
NACA 2412 0 Degrees Angle of Attack Large Chord [C]
NACA 9412 10 Degrees Angle of Attack [D]
As you can see above, the "standard" F1 Rear Wing produces significant Drag due to the high Coefficient of Lift. The goal is to reduce Drag. So one method is to reduce the Angle of Attack, thereby reducing the Coefficient of Lift. This is shown in the Image B. Next, a large Chord F1 Wing is shown. Though the Coefficient of Lift isn't changed by the larger Chord, the Aspect Ratio is worse, and additionally extra bodywork is exposed to the Free Stream. This is shown in Image C. Lastly in Image D, I show the effect of Camber on the wing. You can see that higher Camber, such as that in the NACA 9412, creates a higher Lift Coefficient and therefore increases Induced Drag. You can see the stronger Vortices than its Image B counterpart with lower Camber.
|Large 2412 0AOA||16.65||40.79||2.44985|
In conclusion the CFD showed the correct Trends to match the Theory. In order to reduce Drag, one can do things such as reduce the Angle of Attack, or Camber in order to reduce the Coefficient of Lift and therefore reduce the Induced Drag. Another option is reducing the Chord of the wing, which reduced both Wetted Area and increases Aspect Ratio, which helps reduce the Induced Drag.
If you guys are interested in a more detailed Article on this topic, please let me know. Otherwise I will assume this was sufficient.