carrera s 2020 streamline showing flow separation

Porsche 911 Carrera S has been one of the most aerodynamic studied car in the 911 series. Due to the Porsche iconic body shape, its the aerodynamic has been a major issue on its performance.

In the old days, the lift problem at high speed made the car difficult to handle. This problem is more prononce with modern high power engine.

Drag is also an inevitable large on Porsche as the steep windscreen and back slope are unfavourable to air flow. We will discuss these two in the following sections.

Length4519 mm
Width2024 mm
Height1302 mm
Wheel base2450 mm
Weight distribution (Front:rear)39:61

Simulation model

A full scale model is provided from Naviertec and put into virtual wind tunnel for testing. Wind speed is 27.7 m/s and with moving floor.

ResultsValueCoef.Official Coef.
Drag108 N0.2740.29
Lift6.41 N0.016
Pitching (-ve down)-329 Nm-0.339
Force results from simulation (Wind speed 27.7 m/s)

Drag and lift

From the simulation results, we can see that drag is quite high for a 2020 sport car. The lift is negotiably small with a high pitching down moment which gives downforce on front axle and lift on rear axle. This disturbtion could possibly make the oversteering behaviour from the rear bias weight even worse.

A retracble rear spoiler is added to deploy during breaking and cornering, as seen from the photo, for lift reduction.

Credit: Carnerd TV

The pressure plots clearly illustrate the sources of downforce and lift. High pressure area at the front splitter (Red) contribute a large proption of downforce to the front axle

The centre plane velocity plot shows that air flow at the back slope window follows the surface to prevent air separation and creates drag.

Velocity at centre plane

It can be seen from the total pressure contour that loss around the centerline of the car is minimal which agree with the conclusion from the velocity plot.

Loss

A large region of loss exist at the rear end behind the wheels. This is loss coming from the wake of rear wheels and also from the flow separation at the rear corners at the rear bonnet. The steamline plots below confirm with this point of view.

Conclusion

Even with a drag reduction from previous generation 0.3 to 0.29, the unique body shape of the Porsche brings relativly high drag and lift comparing to modern sport coupe. The retractable spoiler may help with reducing rear lift. A ducktail on the rear end of the spoiler may reduce drag by the introducing high pressure zone at the rear.