Discuss About The Aerodynamics Effective Computational Methods
The Importance of Aerodynamics in Racing Cars
Discuss About The Aerodynamics Effective Computational Methods.
Aerodynamics is a very important element in the performance of racing cars. The speed and efficiency of these cars are largely influenced by how air flows around their bodies (Diasinos, et al., 2014). This drives designers of the cars to ensure that air flow round the cars’ wings provide minimal air drag force and reasonable downward pressure. A racing car’s wing comprises of three main parts: top/front wings, bottom/rear wings and wings on both sides of the car. These components have a direct impact on the car’s aerodynamic downforce. Downforce refers to the downward thrust that is created by the car’s aerodynamic characteristics. The front wings are more aerodynamically efficient than the other parts because they affect how air flows at the other components (TotalSim Ltd, 2016). These wings create downforce that is responsible for enhancing grip of the car’s front tires, and also optimizes air flow to the other parts of the car (Formula One World Championship Limited, 2017). The wings on both sides of the car are responsible for guiding flow of air front the front to the rear side. The rear wings are less aerodynamically efficient because air flow at them is affected by other components of the car such as front wheels, front wings, mirrors, exhaust, driver’s helmet, etc. Nevertheless, the rear wings are expected to produce more than double the downforce produced by the front wings for the driver to handle and balance the car efficiently. To achieve this, the aspect ratio of the rear wing is larger. These wings also have additional elements that help in increasing downforce. Both front and rear wings are mainly used in acceleration, cornering and braking forces (Rapid-Racer.com, 2016).
This project will examine the aerodynamics of the entire wing, which has to be designed such that it reduces drag and increases downforce (reduce lift and increase grip) so that the car can move at its design speed, even when negotiating a corner, without being lifted off the track. Findings from the project can be used to optimize the design of racing car’s wings, especially their shape (cross-section, surface area and aspect ratio) and orientation (angle of attack). This will be of great importance in the manufacturing industry of racing cars as it will help to increase speed, safety, performance and fuel efficiency of racing cars. Other sections of this report include: literature review; research question, aims/objectives and sub-goals; theoretical content; experimental set-up; results, outcome and relevance; project planning; and conclusions.
Components of Racing Car Wings and Their Effects on Aerodynamic Downforce
Performance of racing cars depends on a wide range of factors, including the engine, road, suspension, tires, driver and aerodynamics. In the recent years, aerodynamics (i.e. movement of air around racing cars) has become very critical in race car design because it helps designers utilize the principle of downforce (negative lift) (Katz, 2006). Race car wings operate on the same principle as wings of aircrafts, but in the reverse. The race cars have two sides of the wing, and the speed of air on each side is different, creating a pressure difference that is called Bernoulli’s principle. The balancing of this pressure causes the wing to move towards the low pressure zone. Therefore the race car wings are designed to create adequate negative lift (aerodynamic downforce) so as to attain optimum balance.
Several decades ago, race cars were designed with high mountings and movable wings to generate aerodynamic downforce. But regulations were introduced in 1970 to limit the location and size of wings so as to reduce the number of accidents. The concept of designing wings that increase downforce started in mid 1970s and has been improving ever since. Today, the freedom of aerodynamicists is very limited in relation to the width, height and location of wings on race cars (Axerio-Cilies, et al., 2012). Front and rear wings are the most typical aerodynamic devices on racing cars. These devices account for about 60% of the total downforce generated by a race car (Formula One World Championship Limited, 2017). Designers of these cars depend on computational methods to determine the type of wing profiles to use based on the downforce requirements of the specific track that the racing cars will be used. Besides wings, downforce of race cars is also optimized by use of other devices such as front splitters, air dams, rear spoilers/diffusers and aerodynamic under-bodies, among others (Roberts, 2013). Some of the aerodynamic components of racing cars are shown in Figure 1 below (Rapid-Racer.com, 2016).
The relationship between aerodynamic drag and downforce with air speed is as follows:
Fdrag or Fdownforce α S²air (where Fdrag = drag force, Fdownforce = aerodynamic downforce, and S = air speed.
When a racing car is negotiating a corner, it is subjected to three forces, as show in Figure 2 below. F is centrifugal force and it increases with increase in car speed; Ffr is centripetal force and it balances the centrifugal force (Ffr is also proportional to N (normal force) that pushes the car downwards; and μ is frictional coefficient and is determined by the grip between the car and road (Mark, 2017). These forces guide the design of appropriate racing car wings.
Design and Optimization of Racing Car Wings
There are various design tools that can be used to examine the aerodynamics of racing cars. These include CFD, wind tunnel testing and track testing, among others. This project will focus on CFD and wind tunnel testing (Hetawal, et al., 2014). In these methods, models of racing cars are created then their simulations developed so as to establish the behavior of the cars as they interact with air and he road (Doig & Barber, 2011); (Diasinos, et al., 2013).
CFD is an analytical tool and method used to create simulations of various transfer phenomena such as heat transfer and fluid flow. The accuracy of results obtained from CFD was verified by the wind tunnel test. There are numerous studies that have been conducted before on investigating aerodynamics of cars using wind tunnel and CFD methods. One of these studies involved using wind tunnel test to investigate stability of a passenger car under crosswind conditions and traveling at very high speed (Kee & Rho, 2014). Other researchers created a steady-state aerodynamic model to predict the performance of a race car and compared results with simulation results of a conventional steady-state model (Mohrfeld-Halterman & Uddin, 2016). Another study involved establishing important aerodynamic flow characteristics of front wing of a racing car operating at an increasing yaw angle (Altinisik, et al., 2015). In a different study, flow characteristics and aerodynamic loads of a rear wing were analyzed by developing a computational model using CFD (Buljac & Dzijan, 2016). Another similar study involved use of wind tunnel test to establish aerodynamic factors that affect formation of overtaking opportunities in car racing competitions (Soso & Wilson, 2006). A wind tunnel test was also performed in another study to investigate pressure distributions and drag forces at increasing yaw angles of a racing car model. Last but not least, a combination of CFD and wind tunnel test was used by a researcher to investigate aerodynamic drag so as to establish reasons for increasing drag coefficients of passenger cars (Zhang, 2012).
These previous studies show that there is enough content with which the results obtained from this project can be compared. Therefore this project will provide vital information on the comparison between wind tunnel test and CFD simulation
The main research question in this project is: what is the relationship between results obtained from wind tunnel test and CFD simulation of a racing car wing? Based on this question, the main objective of the project is to compare results obtained from CFD simulation and wind tunnel test of a racing car wing. To achieve this objective, a wind tunnel test will be performed on a racing car wing then a CFD simulation model of the same racing car wing will be created using CFD software.
Comparison of Wind Tunnel Testing and CFD Simulation for Racing Car Wing Analysis
The hypothesis to be tested in this project is that the results obtained by analyzing a racing car wing using wind tunnel test are similar to those from CFD simulation and provides useful information that can be used to optimize the design of racing cars so as to improve their speed, efficiency and safety. These analyses are done on the basis of aerodynamics of a racing car, which is largely influenced by aerodynamic moment and aerodynamic force. These two components are influenced by factors such as sideslip angle, body shape and driving speed of the car. The aerodynamic force and moment comprise of six components: three forces and three moments – drag force, side force, lift force, rolling moment, yawing moment and pitching moments. The six components are composed around x, y and z axes. The tests in this project will be done by applying the lessons learnt in similar studies conducted before.
Wind tunnel test is the commonly used method of analyzing aerodynamics of vehicles and vehicle parts. This method is widely used by the National Aeronautics and Space Administration (NASA) in it aircraft and spacecraft projects (Hitt, 2017). The method will be used in this project so as to compare results obtained with those from CFD software. The wind tunnel to be used in this project is that available at the university laboratory or any nearby company with a wind tunnel facility. The test will be conducted in consideration with the limitations of the wind tunnel, such as its size, wind speed range and system of data acquisition. For the testing of the racing car wing’s aerodynamic characteristics to be performed, a strain gauge representing the aforementioned six aerodynamic component forces will be designed. This balance will be used to measure the three aerodynamic forces and three aerodynamic moments of the wing. The racing car wing sample will then be connected to the upper part of the wind tunnel system by mechanical connection. A tray will then be fixed at the bottom of the wind tunnel. Yaw angle of the wing can then be adjusted by rotating the tray. The tray will be connected to the strain gauge balance through the bottom support. The connection between the strain gauge balance and tray will also help in ensuring that the lift height of the wing being tested is not affected by the surface boundary layer. The strain gauge balanced will be comprised of several beams that will be used to measure different aerodynamic components, including: normal force, pitching moment and axial force. There will also be strain sensors installed in the system to measure the force and torque of the wing. Some of the limitations of wind tunnel include: possible mechanical failures; it must be conducted by a trained and qualified technician; it must be designed for testing racing cars; data repeatability; it gathers limited information compared with CFD test; and systematic and random errors; among others.
Previous Studies on Aerodynamic Performance of Racing Cars using CFD and Wind Tunnel Testing
Flow field simulation model of the wing sample will also be established by use of computational fluid analysis software under the same conditions as those of wind tunnel test. This experiment will be performed in the university computer lab. The main task will be to set the right inputs in the CFD software, run it and obtain the required model data, graphs and simulations. One of the limitations of CFD simulation is that it will largely depend on the racing car wing model that will be used. This means that if the model will have any problems, such as design problems, then the results of CFD simulation will also be affected. (Chandra, et al., 2011) Other limitations include: computational power, computational efficiency, and knowledge and skill of the user. However, results obtained from CFD simulation will have to be validated with those from wind tunnel testing. This is because CFD simulation conditions are more ideal but wind tunnel testing is carried out in conditions that are close to real conditions.
Simulation results from CFD software and experiment results from the wind tunnel test will be recorded and compared. For each of these experiments, the values of downforce and drag force (in newton) of the wing sample will be measured against angle of attack (in degrees Celsius) at different wind speeds. Graphs of downforce vs. angle of attack and drag force vs. angle of attack will then be drawn. It is expected that the simulation and wind tunnel test results will be similar with a very small percentage difference of about 5%.
It is also expected that simulation results will be more accurate hence more reliable. This is because the conditions under which simulation of the wing is carried out are near-perfect hence sources of error are minimal. As a result, simulation results are the recommended for use when performing detailed analysis of the aerodynamics of a racing car wing in varied conditions. The CFD software will also calculate the aerodynamic coefficients influence of the racing car’s sideslip angle and speed. This will be done by setting gradient and sideslip angles at different values. Measures of crosswind velocity and windward velocity at different sideslip angles will then be determined. The relationship between aerodynamic force coefficient, sideslip angle and speed, and that between aerodynamic moment coefficient, sideslip angle and speed will then be created using the CFD software. Simulation results will also be used to determine values of the six components (drag force, side force, lift force, rolling moment, yawing moment and pitching moments). In this calculations, it will be assumed that the speed of the racing car will be constant. The route of the vehicle and road adhesion coefficient will also be predetermined.
Research Question, Aims/Objectives and Sub-Goals
The results obtained from this project will provide useful information on how different factors such as speed of car, windward speed, crosswind speed, yaw angle, angle of attack and road surface affect the aerodynamic components of a racing car. This information can be used by engineers and designers to design wings that optimize the performance of racing cars by reducing drag force and increasing downforce.
The main tasks in this project will be to perform the two experiments: CFD simulation and wind tunnel testing. These experiments will demonstrate how air moves around racing car wings. The first task of the project will be to test a racing car wing sample in a wind tunnel at the university lab or nearby facility. The second task will be to perform aerodynamic simulation of the same wing sample using CFD software. In both these tests, all the six component forces (drag force, side force, lift force, rolling moment, yawing moment and pitching moments) and torques will be measured and calculated at different speeds then analyzed. The third task will be to compare results from the two tests and verify CFD simulation results using wind tunnel test results. The fourth task will be to establish the aerodynamic model of the racing car wing sample being tested. Therefore the overall project plan is as follows:
|
No. |
Activity |
Estimated duration (days) |
|
1 |
Project preparation |
10 |
|
2 |
Wind tunnel equipment familiarization |
2 |
|
3 |
CFD software familiarization |
2 |
|
4 |
Wind tunnel test execution |
1 |
|
5 |
CFD simulation execution |
1 |
|
6 |
Data collection |
2 |
|
7 |
Data processing and analysis |
16 |
|
8 |
Final report preparation |
10 |
|
9 |
Project presentation |
1 |
|
Total |
45 |
|
3d |
6d |
9d |
12d |
15d |
18d |
21d |
24d |
27d |
30d |
33d |
36d |
39d |
42d |
45d |
|
|
Project preparation |
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|
Wind funnel equipment familiarization |
|||||||||||||||
|
CFD software familiarization |
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|
Wind tunnel test execution |
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|
CFD simulation execution |
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|
Data collection |
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|
Data processing and analysis |
|||||||||||||||
|
Final report preparation |
|||||||||||||||
|
Project presentation |
Conclusions
This project will present one of the most reliable and effective methods of investigating aerodynamic characteristics of a racing car wing. The investigation will be done using two effective methods that are commonly used for this purpose computational fluid dynamics simulation and wind tunnel testing. This will be done by establishing an appropriate racing car’s aerodynamic model and subjecting it to the two tests so as to measure six components: six aerodynamic forces: drag force, side force, lift force, rolling moment, yawing moment and pitching moments. The computational simulation results obtained will be verified with the wind tunnel test results. The racing car wing’s flow field model will also be established and its respective aerodynamic equations obtained. Last but not least, he racing car wing’s aerodynamic forces and torques will be calculated. The findings from this project will be used to optimize design of racing car wings so as to make racing cars safer and better.
In future projects, similar tests should also be used to investigate new materials for racing car wings. This will help in identifying materials that are easily available, easy to manufacture, environmentally friendly, affordable and sustainable.
Theoretical Content on Aerodynamics of Racing Cars
References
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Axerio-Cilies, J., Issakhanian, E., Jimenez, J. & Iaccarino, G., 2012. An Aerodynamic Investigation of an Isolated Stationary Formula 1 Wheel Assembly. Journal of Fluids Engineering, 134(2).
Buljac, A. & Dzijan, I., 2016. Automobile Aerodynamics Influenced by Airfoil-shaped Rear Wing. International Journal of Automotive Technology, 17(3), pp. 377-385.
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