FSAE car

• Given Problem:-

Phase 1: Geometry cleanup

• Cleanup the 48 errors
• Flag the front wings, rear wings, tyres, suspension links as separate boundaries
• Create a virtual wind tunnel
• Ground plane reference is provided in the lower end of the tyres. There will be a \"flat section\" in all the 4 tyres. This refers to the location of the ground plane. You will have to create the ground plane and perfectly merge it with the tyres.
• Run a virtual wind tunnel no-hydro test and a coarse simulation test to prove that you have finished face 1 correctly.
• For phase-1, the virtual wind tunnel boundary conditions and physical models can be assumed. If your simulations run, you will be given full graded for this phase.

Phase 2 - Detailed Setup

ABCD Racing company is looking to perform Aero Simulations for their FSAE vehicle and they have hired you to do the job. The suspension team wants a detailed report on the total downforce on individual components. They have two races in this upcoming season.

Race details are as follows

Race-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

Race-2

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

For both theses races, summarize the CFD operating conditions. Create two separate case setup and send them to us. We will review and run these simulations in our cluster for you to post-process.

• Software used-

1. Converge CFD Software

2. Cygwin

3. Paraview

• Geometry -

Fig.1, FSAE Car

Fig.2, Wind Tunnel

• Steps Involved while solving this challenge-

1. FSAE car geometry was downloaded from the given link. But the car geometry has many errors. The first challenge was to remove errors and make the geometry error-free. After encountering the different errors, I made sure that all errors are cleaned and removed. Now the geometry becomes clean again.

2. The second challenge was to create boundary flaggings. Boundary flagging was time-consuming due to the type of geometry.

3. After cleaning error and done boundary flagging correctly, we need to create a wind tunnel around the FSAE car. Wind tunnel creation was also time-consuming due to geometry complexity.

This setup requires 2 cases. In the first case, we have the following condition-

Race-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

and In 2nd case, we have the following condition-

Race-2

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

4. We first run the case for straight track condition where we need to use 75kmph speed. We setup case according to it an run.

5. In the second case, we need to find a weighted average of all turns conditions. So after calculation, the answer was 49.5 Degree. ((0.70*45)+(0.20*80)+(0.10*20)=49.5)

6. After creating the wid tunnel, we will make sure that it is not showing any error and then we will export the file into Cygwin to run the simulation.

7. Finally, we will post-process the result in converge and view the whole case in ParaView.

• Case setup Important Parameters:-

1. Application- General Flow

2. Solver- Transient solver with full Hydrodynamic Flow

3. Start Time- 0 sec.

4. End time- 3.12 seconds for Straight path and 5.2 seconds for lots of turn path.

5. Initial time step and minimum time step- 1e-05 sec

6. Velocity in X direction- 20.83 m/s for straight path and 12.5 m/s for lots of turn.

7. Region temperature- 300k

8. Region Pressure- 101325 Pa

8. Turbulence Model- Standard K-w 2006

Turbulence modelling tries to represent Reynolds stresses in terms of time-averaged velocity components. The common turbulence models are classified on the basis of the number of additional transport equations that need to be solved along with the RANS equations. For the purpose of this project, Standard k - w.; the model is chosen which solves two extra transport equations to resolve the Reynolds stress tensor. This model is an improvement over the existing k - e turbulence model and it addresses some of the key disadvantages associated with k - e: Poor predictions for swirling & rotating flows and flows with strong separation, two of the key flow characteristics associated with FSAE car. Moreover, k - w models have an enhanced wall treatment or an Automatic Wall Function. What this does is give a good range of Y+ values.

9. Base Grid- 0.5m

It is based on the wall spacing value calculated by taking the desired value of Y+. The computation is based on the flat plate layer boundary layer theory. The variables input used are free stream velocity, density, characteristics length, desired y+ and dynamic viscosity.

1. Reynolds Number-

2. Skin friction-

3. Wall shear stress

-

4. Friction Velocity-

5. Wall Spacing-

Based on these formulas and calculation we were able to get wall spacing y. The wall spacing was coming near 0.25 but as we know that it will be a very fine mesh and we don\'t possess such computing power. So we have taken mesh as 0.5m in x,y,z directions.

10. Fixed Embedding- 13 Embeddidings

1. From Embedding 1 to 12-

• Entity type= Boundary
• Mode=Permanent
• Scale=1
• Embedded layer=1

2. Embedding 2-

• Entity type=Box
• Mode=Permanent
• Scale=2

10. Boundary conditions- 1. Inlet- Inflow Type, Pressure(Zero Normal gradient), Velocity(Specific value of 20.83 m/s), Temperature(Specified value of 300k)- For straight path.

For a lot of turns, Velocity will be 12.5m/s

2. Outlet- Outflow type, Pressure(Specified value of 101325 Pa), Velocity boundary condition(Zero normal gradient: Backflow),Temperature(Specified value of 300k).

3. Bottom- Type- Stationary Wall,

4. Symmetry- Symmetry

5. Body-Stationary Wall

6. Spoiler-Stationary Wall

7. Front wheels-Stationary Wall

8. Rear wheels-Stationary Wall

9. Front right suspension-Stationary Wall

10. Front Left suspension-Stationary Wall

11. Rear right suspension-Stationary Wall

12. Rear left suspension-Stationary Wall

13. Front wing right-Stationary Wall

14. Front wing left-Stationary Wall

15. Underbody-Stationary Wall

16. Human-Stationary Wall

• FSAE car Explanation-

The Formula-SAE car shown above falls under the category of Open-Wheel Race Cars.

Formula SAE, commonly known as FSAE, is a student design competition organized by Society of Automotive Engineers (SAE). In the growing technology and engineering process, Computational Fluid Dynamics (CFD) has played a huge role in the design of such aerodynamic cars. CFD analysis on an FSAE car can give vital information as to where the maximum drag occurs, or vorticity of the space behind the car. This information can help design the best FSAE car and beat the competition.

The role of aerodynamics in race-cars is to generate downforce and drag wherever necessary and thus help improve vehicle performance.

The study aims to perform CFD simulation for a Suspension Team of a racing company which needs data on the downforce generated by individual components using a software tool known as Converge and later post-processing it in Paraview. Using this data, the team would decide on the suspension spring stiffness, the types of tyres to be used. improvement of the design of suspension control arms and focus on placing the centre of gravity behind the centre of pressure to make the car more stable.

Fig.3, FSAE Car

• FSAE Base Grid-

Fig.4, Mesh Grid

• Straight Path Case-

Fig.5, Straight track Wind Tunnel

Steps to calculate lift and Drag-

1. Open the (test.vtm file case) and then go to filters and select Extract block. then choose the FSAE body and wheels as the block to calculate the lift and drag.
2. Next, generate the surface on block. go to filter select Extract Surface.
3. After that generate the surface normals. Again go to filter, select the generate surface normals and check the box \' compute cell normals \'.
4. To calculate lift. Select the calculator and choose Pressure from the scalar drop-down menu then multiply it with Normals Z In the Result Array name box writes down as lift.
5. To calculate Drag. Select the calculator and choose Pressure from the scalar drop-down menu then multiply it with Normals X. In the Result, Array name box writes down as Drag.
6. Finally, we choose to integrate variables to get the lift and drag force value in the paraview.
7. Select components from extract blocks and calculate the drag and downforce by using integrate variables window.

Fig.6, Downforce acting on FSAE car on straight Track 1

The downforce is acting on the body as anticipated. This downforce is helping the car to stay on the ground. It\'s just like an inverse Airfoil. The top section has high pressure on it whereas the bottom section has low pressure compared to the top section.

As FSAE car travel at very high speed, it needs to stick to the ground or in easy terms, its wheel traction with the ground should be as high as possible. So the downforce makes sure that it works in such a manner that it pushes body downwards and help the car to make traction with the ground.

Fig.7, Downforce acting on FSAE car on straight Track 1

Fig.8, Drag acting on FSAE car on straight Track 1

Fig.9, Drag acting on FSAE car on straight Track 2

Fig.10, Y+ Value

Fig.11, Downforce and Drag component on each component(Straight Path)

Fig.12, Plot of Downforce on each component

The car body generated the maximum amount of downforce as expected but we can see that spoilers(rear wing) and front wings generate very less amount of downforce.

It can be improved by increasing the angle of attack of wings.

Fig.13, Plot of Drag on each component

Here, the body is generating the least amount of drag whereas the underbody is generating the maximum amount of frag.

• Lot\'s of Turn Path Case-

Fig.14, Lot\'s of turn track Wind Tunnel(49.5)

Fig.15, Downforce acting on FSAE car on lot\'s of turn Track 1

Fig.16, Downforce acting on FSAE car on lot\'s of turn Track 2

Fig.17, Drag acting on FSAE car on lot\'s of turn Track 1

Fig.18, Drag acting on FSAE car on lot\'s of turn Track 2

Fig.19, Drag acting on FSAE car on lot\'s of turn Track 3

Fig.20, Velocity acting on FSAE car on lot\'s of turn Track 1

Fig.21, Velocity acting on FSAE car on lot\'s of turn Track 2

Fig.22, Downforce and Drag component on each component(Lot\'s of Turn)

Fig.24, Plot of Downforce on each component

Fig.24, Plot of Drag on each component

• Conclusion-

After analyzing the data and the result, it was observed that tires generated a portion of overall drag. To reduce drag on tire, wheels can be covered to make it more aerodynamic. Due to regulation, full covering might not be allowed, but if partial bodywork is permitted, placing converging fairing behind the wheels provides maximum benefit.

Front wing did not generate much downforce than needed, thus, the front wing should be redesign to increase the overall downforce on the car.

The car body was rotated at an angle of 49.5 degree which is a side slip angle and the tire experiences more load because of turning and high-velocity region in the nose and the air ducts then the low-pressure region in the flow separation region streamline visualization will create drag into rn both combine to produce lift. ( Lot of turns)

The flow over wheels where the top surface of the wheel experiences the higher velocity because the flow over there creates the more the flow front wings where high pressure on top and low pressure on the bottom. The two endplates are fixed to prevent the formation vortices here the vortices are seen at the end so additional drag increases. To reduce the drag is to reduce the airfoil thickness and adding flaps like in an aeroplane.

The flow over the rear wing as seen that it creates lift force over the corners by seeing the velocity profiles. This because of the generation vortices and the airfoil in the car wing usually have low aspect ratio and in turn, it creates the drag behind the body and also reduces the angle of attack of free stream air. To improve the lift is to increase airfoil thickness and also increase the height of endplate. The Y plus is uniform throughout the body. The forces on the suspension links are very low there is a need in change of suspension.

Links to Both cases-

1. Straight path case-

https://drive.google.com/drive/folders/1tNIe1DbJ3z3qg_SsUdcGtUzIR0-0bR97?usp=sharing

2. Lot\'s Of Turn Path-

https://drive.google.com/drive/folders/1PvjCdIoWf9pfKenekI32R1o2Msv4Q6lv?usp=sharing