FSAE DRS

Leonardo Crivellaro – leonardo.crivellaro@studenti.unipd.it
 

Introduction

The topic of the project is the Drag Reduce System (DRS) for the formula SAE car MG13.18 of the RaceUp Team of University of Padova.

 

1

Fig.1 : MG 13.18

In particular the rear wing is composed of :

① Main Flap

② End Plate

③ Flap 1

④ Flap 2

⑤ Joint _L

⑥ Joint_R

Then it was added:

⑦ Cylinder

⑧ Link 1

⑨ Link 2

 2

Fig.2 : Components of rear wing by  [2] Design MG13.18-RaceUp Team Car285- 2017-2018 – “Rear Wing”

 

Objectives

The targets of this project are mainly to study the kinematics of the system that actives the DRS’s mechanism, determinate the trend of aerodynamic forces according to the inclination of the wings and finally find the reaction forces at the points of attack between the wing and car’s chassis.

The modelling problem

The origin of the model reference frame is fixed to the point where the pneumatic cylinder is linkage with the main flap of rear wing.

So the axes are oriented as:

  • X-axes: coincides with the left side of a car (respect of driver’s view reference frame);
  • Y-axes: coincides with the opposite direction of the down forces;
  • Z-axes coincides with the opposite direction of the drag forces;

The components were designed in the CAD used by the team, then were saved in Parasolid format and finally imported into Adams.

About the properties of mass were manually imported for each bodies and the position of center of mass and inertia were automatically calculated.

The rear wing group is composed of:

  • Main (included the two laterally End Plate)
  • Flap 1 (the middle flap between Main Flap and Flap 2)
  • Flap 2 (the upper flap)
  • Cylinder (represents the pneumatical cylinder that starts the mechanism)
  • Link 1 (represents the piston of pneumatical cylinder)
  • Link 2 (represents the laterally link between Flap 1 and Flap 2)
  • Joint_R (represents the right chassis attack)
  • Joint_L (represents the left chassis attack)

Note that the Joint_R and Joint_L was created only to show the reaction force in the two chassis attack cause of aerodynamics’ force in base of DRS activation

3

Fig.3 : Rear wing group.

 

Than the mainly points of model were insert, such as the centres of pressure of every flap (supposed constant and coincident with the ¼ of length of distance between nose and end of aerodynamics’ Benzin profile) and the attachment points of rear wing:

Point Name x y z Descritpion
FIX 0 129.3 418.3 Middle point between the two real point where the wing is fixed with the car’s chassis
Fix_L -111.7 129.3 418.5 Left-Point where the wing is really fix with the chassis of the car
Fix_R +111.7 129.3 418.5 Right-Point where the wing is really fix with the chassis of the car
CP_Main 0 4.2 157.9 Center of pressure of Main Flap
CP_Flap_1 0 83.6 -156.2        Center of pressure of middle flap
CP_Flap_2 0 190.5 -222.8 Center of pressure of upper flap

Tab.1 : Main point of model.

Than were create the joins:

  • Fixed joint between FIX and Main_Flap
  • Inline joint between Flap_1 and right End_Plate
  • Inline joint between Flap_2 and right End_Plate
  • Revolute joint between Main_Flap and Cylinder
  • Translational joint between Cylinder and Link_1
  • Revolute joint between Link_1 and Flap_1
  • Revolute joint between Flap_1 and Link_2
  • Revolute joint between Link_2 and Flap_2
  • Fixed joint between Fix_R and Ground
  • Fixed joint between Fix_L and Ground

4

Fig.4 : Rear wing group with connectors.

Than were create the force:

The following data were obtained from the CFD simulation of RaceUp aerodynamics’ division at a constant speed of 15 m/s, i.e. 50 km/h ( “[2] Design MG 13.18….”):

  • Main_Flap (costant angle)
Down Force [N] Drag Force [N]
116.1 9.6

Tab.2 : Main Flap CFD data by RaceUp Aerodynamic Division.

  • Flap_1: (20°= Low Load; 40°=High Load)
Inclinazione [°] Down Force [N] Drag Force [N]
20 16.92 11.22
30 28.86 21
40 36.6 33

Tab.3 : Flap 1 CFD data by RaceUp Aerodynamic Team.

By data interpolation the relations between Force and angle were obtained and then import into Adams to generate the aerodynamic forces for the simulation:

formule 1

5

Fig.5 : Excel interpolation of Flap 1 CFD data.

  • Flap_2: (35°= Low Load; 70°=High Load)
Inclinazione [°] Down Force [N] Drag Force [N]
35 22 15.7
52.5 15.9 21.6
70 7.48 26

Tab.4 : Flap 2 CFD data by RaceUp Aerodynamic Team.

 In the same way used for Flap 1:

formule 2

6

Fig.6 : Excel interpolation of Flap 2 CFD data.

 Than the measure of angle of flap_1 and Flap_2 was created in respect of the z-axis;

7

Fig.7 : Angle’s Measures for flaps’ opening.

 

Similarly the measure of aerodynamics’ force, the reaction forces and momentum were created too:

8

Fig.8 : Model’s Force Measures.

 Finally the forces, that during the simulation will be showed, were created:

9

Fig. 9 : Model’s forces.

 

At the end the Grubler count is:

10

Fig. 10 : Grubler’s count.

Simulations and analysis of results

Video: https://youtu.be/-siSn0XVF3s

  • Aerodynamics force vs. Angle Flap 1:

During the flap 1 opening, the downforce’s and the drag force’s trend is in perfect agreement with the interpolation of CFD’s data and also with the functionality of the mechanism because it can be seen that the force decreases when the wing is opened.

The range of rotation of flap 1 is 28.5°.

11

Fig.11 : Aerodynamics force vs. Angle Flap 1.

 

  • Aerodynamics force vs. Angle Flap 2:

Similarly happens with Flap 2 indeed during the flap 2 opening; the downforce’s and the drag force’s trend is in perfect agreement with the interpolation of CFD’s data.

The range of rotation of flap 1 is 59°.

 

 

12

Fig.12 : Aerodynamics force vs. Angle Flap 2.

 

  • Reaction force and Moment:

The fixing points of the rear wing are symmetrical so the reaction forces, which act in the plane of application of aero forces, will be symmetrically distributed in the two points.

So in these points where the rear wing is attached, the reaction force and reaction moment are:

13

Fig.13 : Reaction Force vs. Time.

And the trend of Moment around the x-axis (Pitch Moment) is:

14

Fig.14 : Pitch Moment vs. Time.

 

Obviously the reaction force along x-axis is zero, as can be seen from the following graph:

15

Fig.15: x-Force vs. Time.

Conclusion

Although some approximations have been made in the Drag Reduction System model such as:

  • Moments around y-axis and z-axis were neglected;
  • The centers of pressure of flaps were considered constant;

this mechanism works correctly because when the flaps is opening the dragforce decreases, and also the forces where the rear wing is fixed with the chassis decreases due to the downforce decreasing.

Furthermore this model can will be used to determinate the stresses in attachment points to study the behaviour that the DRS introduces into dynamics of the vehicle of the racing car.

References

[1] www.raceup.it

[2] Design MG13.18-RaceUp Team Car285- 2017-2018 – “Rear Wing”

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