It is important to have a good mental picture of the main flow patterns around the car before trying to improve the design for aerodynamic performance.

Looking for optimal L/D Ratio

The car behaves like a wing. More incidence increases downforce and drag up to the stalling point:

Each point on the curve has a given gradient (L/D ratio). As we increase incidence / downforce / drag, this gradient is reducing meaning that each incremental step in downforce is coming with more and more drag. By changing the rear wing angle, we change the L/D (aerodynamic efficiency) of the car to optimise lap time. Each track has got a ‘required efficiency’ that can be computed from lap time simulation. By knowing this required efficiency, we know where we need to be on the curve and we set up the rear wing angle to get there.

Lift-to-drag ratio curve

For example at Monza, the required efficiency will be high (4:1). At Monaco it will be low (1:1).

We can put more downforce (rear wing angle) on the car for Monaco (but stop before stall point).

At Monza, we can put more rear wing only if the incremental downforce and drag ratio is better than the track required efficiency of 4:1.

Where does downforce come from?

Downforce is mainly created by 3 highly regulated areas of a racing car: the front wing, the rear wing and the diffuser. Each one needs to be carefully designed and set-up to get the best balance possible.

Front wings can be found on single seaters whereas Le Mans car have a complete front bodywork with aerodynamic flaps. Here are some general principles regarding those features:

Front Wing Flow:

Perrinn F1 car front wing flow

Diffuser Flow:

Static pressure P424 floor

Rear Wing Flow:

Streamlines around 424

From CFD to Real Life

Once the aerodynamics of the car has been optimized through CFD, race teams need to ensure the computer simulations and observations in wind tunnel match with actual aero flows when the car is on track. This correlation work is performed thanks ton the following tools:

Aero rakes

Pitot tubes

Flow-vis paint