Ski-WingBruno Ferreira, Melker Nordqvist

Transport ground vehicles are one of the most used transportsystem existing today and. For that reason, many people tendto take their car on their winter vacation to the mountainswhere the roads are icy and slippery. To improve safety forthe travelers in the car and on the roads it is of greatimportance to improve the traction of the car.

It is known that, for high speeds, bodies tend to create a liftforce due to the pressure gradient created between theirlower and upper surfaces. If this lift force gets too high, itcould impact in the loss of traction of the vehicle andtherefore in a loss of the control and possible accident.

One device that could be used in order to compensate this liftforce without adding extra weight to the vehicle is the spoiler.This device acts like an upside-down wing, creating a forcedownwards and keeping the traction under control. It isimportant to notice that those devices could have a negativeimpact in the drag, which leads to a higher fuel consumptionsince the engine has to produce more power to compensatethis extra drag.

INTRODUCTION

OBJECTIVE

The objective of this study is to design a spoiler in a mannerthat the vehicle stays controllable for high speeds withoutincreasing too much the resultant drag.

METHODOLOGY

• ANSYS CFX.

• Compute values for lift and drag coefficients for allsurfaces on car and spoiler for comparison.

• Three different spoiler positions – Top of slope, at the rearof the slope and the last one in between.

• Factor to decide spoiler was the one with lowest L/D ratio

• Study of flow field by use of streamlines.

• Car dimensions 1044x389x288mm.

SPOILER DESIGN

• Three simplified Carving skis.

• Different angles between the skis to create a ”camber”.

• Aero technology ”Flap configuration”

• Total size of the box containing the skis: 60x380x35mmFigure 1: Chosen spoiler configuration

RESULT AND DISCUSSION

Spoiler Without Rear Middle Top

𝐶𝑑 0.3347 0.4213 0.5298 0.5113

𝐶𝑙 0.1003 0.1094 -0.1734 -0.0415

𝐿/𝐷 0.2995 0.2598 -0.3273 -0.0812

Figure 2: Illustrates the flow field around the car without spoiler (left) andthe one with spoiler (right). Notice the increased bubble size behind thecar created by the spoiler, resulting in more drag.

Table 1: Illustrates the values of 𝐶𝑑 𝑎𝑛𝑑 𝐶𝑙 for the differentlocations of the spoiler.

L/D ratio is an aerodynamic efficiency that defines how muchlift can be generated with a certain amount of drag. A highervalue results for better efficiency. However, downforce ispreferable in this case, so, the L/D should be negative and high.Therefore, by examining table 1, it is possible to observe thatthe best spoiler is the middle one. It should be noted that thisconfiguration creates 58% more drag due to the larger wakecreated by the spoiler (figure 2) than the car without spoiler.This is deemed acceptable since it creates 273% moredownforce than the one without.

CONCLUSION

• Improved driving performance and safety due the bettertraction on the car.

• Increased fuel consumption due to more drag.

• With the selected spoiler it was possible to achieve theproposed objective.

ABSTRACTThis study intends to design a spoiler making use of skis, in order to reduce the risk of accidents on the roads by improving the driving performance of a car. To achieve that, simulations were ran with the help of ANSYS CFX, where different configurations were analysed until a design was conceived. The improvements made in the performance were measured by the lift and drag coefficients, which were compared then to a body in the absence of the spoiler. The outcome of

the study was very satisfactory, resulting in an improvement of more than 250% in downforce, in spite of a negative outcome for the drag.