The Aerodynamic Influence of Rim Design on a Sports Car and its Interaction with the wing and Diffuser Flow

Sammanfattning: Global climate change and increasing fuel prices demand more efficientvehicles. Today the automotive industry invests significantly into developingmore efficient engines and to reduce the required force to propel thevehicles. For a passenger car the aerodynamic drag is a dominant partof the total resistance at highway speeds. In the area of sportscars, aerodynamicdrag is even more dominant due to higher speeds and the factthat aerodynamics is also used in order to increase downforce. This resultin contradictory demands as downforce often comes with a drag penalty.There has to be a delicate balance between the two. Even though the fuelprice is not an issue when racing, there is a demand for efficient vehiclesin order to obtain as much performance as possible within the rules.The wheels have been shown to have a large influence on the globalaerodynamic properties of a vehicle. It has also been shown that the localflow field around the wheels and wheel housings is highly dependent ofthe rim design.In this project the influence on the global as well as the local aerodynamicproperties from the rim design was studied. In addition theinteraction between rim design and diffuser was investigated as well asthe interaction between the diffuser and the wing.The simulations showed clearly that a substantial decrease in dragcan be achieved with proper rim design. Blocking the crossflow throughthe rims result in increased static pressure in the front wheel house andthereby an increase in lift, whereas blocking the crossflow in the rear resultin increased downforce due to an increased flow rate through thediffuser. It was however shown that the resulting flow around the rearwheel was highly dependent of the rim design in the front. Furthermore itwas shown that removing the lower wing increase the downforce generatedfrom the upper wing whilst the base wake aft of the vehicle was substantiallyreduced and thus also the driving force for the diffuser leaving itless efficient.