In the Model S review, we have discussed about the effect of spoiler (duck tail) on Model S drag and lift. In this WHAT IF series, the rear spoiler effect will be further investigate on the Model S.

Two different rear spoilers 3D models were provided by Chaos Studio for virtual wind tunnel testing.

1st rear spoiler
2nd rear spoiler

Spoiler

Spoiler has been a popular road car modification for a long time both for aesthetic and aerodynamic reasons. In recent years, car owner install a piece of carbon fibre rear spoiler (duck tail) on the edge of the rear bonnet.

Many researches have been conducted to examine the effect of the spoiler on the aerodynamic and they concluded that its main objective was to reduce drag instead of increasing down force.

Result

Two spoilers were tested separately inside a virtual wind tunnel with the same Model S model as in the previous post under 27 m/s (100 km/h) wind speed.

ResultsOriginalSpoiler 1Spoiler 2
Drag0.260.2460.242
Lift-0.012-0.048-0.167
Pitching (-ve down)-0.128-0.0710.003
Force results from simulation (Wind speed 27.7 m/s)

The force results show that both spoilers reduces the drag by 5.4%. However spoiler 2 generates 3.5 times more downforce than spoiler 1 and 14 times more while comparing to the original.

The pressure plots show that the both spoilers create a high pressure zone (yellow) on the rear bonnet. This high pressure area not only generates down force at the horizontal surface but it also reduces the drag by acting on the vertical surface on the rear window.

Velocity (1st rear spoiler)
Velocity (2nd rear spoiler)

From the velocity plot at the center, it can been seen that spoiler 2 effectively stops air on the bonnet and thus creates a high pressure area (blue) where this area is much smaller for spoiler 1

Conclusion

The results clearly illustrate the improvement on drag and especially on the down force that the spoilers give and with spoiler 2 being the best one in terms of down force generation.