Week 11: FSAE Car Project

Objective:

Simulate and Analyse flow over a FSAE Car for below two cases.

Case 1: 

• Racing track conditions - Lot of turns
• Average lap speeds - 45kmph
• 70% turns at 45 degrees
• 20% turns at 80 degrees
• 10% turns at 20 degrees

Case 2:

• Racing track conditions - Straights
• Average lap speed - 75kmph

 Problem Description

  The aim of this study was to analyze the aerodynamics of the FSAE car geometry shown in Figure 1. The focus was on examining the drag and downforce forces on different parts of the car. The simulations were carried out for two different car positions, one on a straight track and one on an angular track. For the angular track, the observations were made at an average angle of 49.5 degrees, which was calculated as a weighted average of the angles of 45, 80, and 20 degrees with weights of 0.7, 0.2, and 0.1, respectively.

Geometry

Fig 1: FSAE Car Geometry

Fig 2: Case setup for case 2

Fig 3: Case setup for case 1

Wind Tunnel Dimensions:

Case 1: 32.5 m x 6 m x 2.5 m

Case 2: 32.5 m x 5 m x 2.5 m

Initial Conditions

Case 1

Air (0.7 N2 0.3 O2) @ 300K at 12.5 m/s

Case 2

Air (0.7 N2 0.3 O2) @ 300K at 20.833 m/s

Boundary Condition

1. Inlet velocity at 300 K

       Case 1: U=12.5m/s

       Case 2: U=20.833 m/

    2. Exit total pressure at 101325 Pa @300 K

    3. Top and side walls - symmetry boundary condition.

    4. Law of wall boundary condition for airfoil at 300K.

Simulation Parameters

Transient Solver

Fully Hydrodynamic Simulation mode 

Compressible Gas Flow Solver

Start time: 0 s.

End Time: 1 s.

Time Interval for the 3D output  file: 0.01 s (Total 100 frames)

Time Interval for the Text output file: 1e-7 s

Initial time-step: 1e-9 s

Minimum time-step: 1e -9 s

3-sec Maximum time step 

Standard k-ω (2006) Turbulence model

Result and Analysis:

Below we can find the snippets of the Result & Analysis of the simulation:

• CASE 2:

Fig 4: Velocity contours - Case 2 - Top

Fig 5: Velocity contours - Case 2 - Bottom

Fig 6: Pressure contours - Case 2 - Top

Fig 7: Pressure contours - Case 2 - Bottom

Fig 8: Drag force - Case 2 - Top

Fig 9: Drag force - Case 2 - Bottom

Fig 10: Downforce - Case 2 - Top

Fig 11: Downforce - Case 2 - Bottom

Fig 12 : Velocity contours - Mid plane

• CASE - 1:

Fig 13: Velocity contours - Case 1 - Side

Fig 14: Velocity contours - Case 1 - Bottom  

Fig 15: Pressure contours - Case 1 - Side

Fig 16: Pressure contours - Case 1 - Bottom 

Fig 17: Drag force - Case 1 - Side

Fig 18: Drag Force - Case 1 - Bottom

Fig 19: Downforce - Case 1 - Side

Fig 20: Downforce - Case 1 - Bottom

Fig 21: Velocity contours - Case 1 - Mid Plane

Conclusion: 

• The observations indicate that in both cases, the body experiences the highest positive drag (significantly higher than other components) and the underbody experiences the highest negative drag.
• In terms of lift force, the underbody generates the highest lift and the body produces the highest downforce. As the surface area increases, the total drag in case 2 is 35.2298 N and in case 1 it is 56.618 N.
• The total downforce in case 2 is -5429.52 N and in case 1 it is 5388.52 N, which is nearly the same since there is no change in geometry along the z-axis.
• In case 2, the force along the y-axis is almost zero due to the symmetry of the body, whereas in case 1, it experiences a force of -29.95 N, which is comparable. The contribution of forces from the tires is significant after the body and underbody, but their effect will change when they start rotating and also contribute to lift.
• The human is experiencing the highest intensity of drag, which can be mitigated by using a windshield. Except for the rear wing, other parts do not contribute significantly to any of the forces.
• Both cases exhibit a wake region of approximately 4-5 m, which must be reduced by modifying the geometry.