As the very first post of this website, the BMW X1 xDrive28i is chosen to study its aerodynamics performance. The 3D model was created by Chaos Studio based on a real X1.
| Length | 4455 mm |
| Weight | 1798 mm |
| Height | 1544 mm |
| Wheel base | 2759 mm |
Aerodynamics simulation
A full scale model is put into virtual wind tunnel for testing. Wind speed is 27 m/s and without moving floor.
| Results | Value | Coef. | Official Coef. |
|---|---|---|---|
| Drag | 314 N | 0.334 | 0.33 |
| Lift | 1006 N | 1.071 |
Drag from simulation agrees very well with the official figure. As expected, the drag is significantly higher than typical sedan (Model S 0.24) because of its hatchback design.
Large amount of lift is generated from the low pressure region on the roof and the A pillar (see Coefficient of pressure (Cp) plot). Without a downward slope surface like on a fastback car, air pressure cannot recover to free-stream pressure and thus no down force is generated.
Cp plot on surfaces (Red: Cp = 1, Blue: Cp = -1) 
Cp plot on surfaces (Red: Cp = 1, Blue: Cp = -1) 
Cp plot on surfaces (Red: Cp = 1, Blue: Cp = -1)
Streamline plots clearly show that a large dead zone exists at the back where air flow cannot follow the surface and separate. The low pressure in the dead zone, couples with the large area of the back of the car, creates large drag.
Streamline colored with velocity (Red: 27 m/s, Blue: 0 m/s) 
Streamline colored with velocity (Red: 27 m/s, Blue: 0 m/s)
Total pressure isosurface plots illustrate regions contributing to drag. Total pressure in these regions are less than freestream and thus dissipate flow energy.
Wheel rim and side mirror also contribute quite large amount of loses.
Isosurface (Total pressure= 0 Pa) 
Isosurface (Total pressure= 0 Pa)
