4. Aerodynamics
4.5 The complete aerodynamic package
In this report the areas where the biggest gains in terms of on track performance can be made have been looked at in the most detail. However the aerodynamic package should always be considered as a whole and when it comes to simulating the race car the overall coefficients need to be known. The nose cone, body, side pods and wheels all contribute their own coefficients. This section aims to find suitable estimates for these coefficients.
The nose cone controls the airflow over and under the rest of the car. The nose cone and the body of the car have been designed to have as close to a teardrop shape as possible. Teardrop shaped bodies are extremely streamlined and it is the desire by most formula student teams to get as close to this overall shape as possible. From a simulation run using a simplified model; CL and CD of the body and nose were found to be -1.53 and 0.122 respectively. To account for the simplicity of the model these values were adjusted to make them more realistic.
CL
=−1.2 C
D=0.2
The wheels of a formula student race car have to be uncovered resulting in the wheels being one of the primary contributors to the aerodynamic coefficients. Uncovered wheels come into direct contact with airflow. The wheels have a radius of 261 mm; their drag coefficient can be equated to two to three times that of a cylinder with the same radius.
CL
=1C
D=0.45
The sidepods contribute significantly to the overall drag of the car and produce a little lift. Ducted sidepods have been selected in this report because they have a significantly improved flow rate of air through the radiator over sidepods without cooling ducts. These ducted sidepods have
coefficient equal to:
CL
=0.13 C
D=0.4
Aerodynamics
4.6 Conclusion
The overall coefficients of the car, including the wing package, are simply combined with addition:
CL
=−2.16 C
D=1.23
Here A, in the equations for lift and drag, if referring to the frontal area of the car. The value of L/D for a formula student car with high wheel drag, wings and underbody, operating nearer the CL max than L/D max will be in the range of -1 to -2. For this car L/D is -1.76 and therefore seems
reasonable. It is clear to see that downforce has been prioritised in this report; the car has quite a large drag coefficient. However as proved in this chapter the increased downforce will lead to quicker cornering velocities, resulting in faster lap times. The overall aerodynamic performance of the car can still be improved with the use of features such as gurney flaps, undertray tunnelling and skirting. Improvements can still be made after manufacture; wing angles and the ride height can be adjusted to find the optimum positions on the track.
4.7 References
[4] Howatson, A., Land, P., Todd, J., “Engineering Tables and Data”, 2009, p. 46 – 48 [5] [Online] http://www.airforme.co.uk/
[6] [Online] http://en.wikipedia.org/wiki/Carbon-fibre-reinforced_polymer [7] [Online] http://www.acpsales.com/home.html
[8] Douglas, J., Gasiorek, J., Swaffield, J., “Fluid Mechanics”, vol. 4, 2001, p. 142 [9] [Online] http://en.wikipedia.org/wiki/Diffuser_(automotive)
[10] [Online] http://www.racecar-engineering.com/technology-explained/diffusers-engineering-basics-aerodynamics/
[11] [Online] http://en.wikipedia.org/wiki/Computational_fluid_dynamics [12] 2015 Formula SAE Rules, T6.1.1, 2015, p. 57
[13] Pehan, S., Kegl, B., “Aerodynamic Aspects of Formula S Racing Car”, 2002, p. 1112 [14] [Online] http://www.airfoiltools.com/
[15] [Online] http://en.wikipedia.org/wiki/Angle_of_attack
[16] Dahlberg, H., “Aerodynamic development of Formula Student race car”, p. 5 [17] Howey, D., McGilvray, M., Lohr, R., “Formula Student 3YP – Simulation of vehicle performance”, 2014
and Packaging
5 Chassis and Packaging
5.1 Introduction
The chassis is the main physical framework of a vehicle, being compared to an animal’s skeleton in the way it is responsible for both protecting everything contained within, for example the engine, transmission and driver, and for it to support all the vehicular components and the payload placed upon it, whether it be providing a cell for the driver or a connection point to the suspension and wheels. The aim for the chassis is to be rigid enough not to deform too greatly when the car is in use, such as cornering and accelerating, as this would make the effects of fine-tuning suspension redundant. On top of rigidity, safety is a crucial aspect to be considered, especially in the case of dealing with a racing car, which is put under more extreme conditions than a normal car.
The chassis can be constructed as a separate frame and body. The frame is designed to support the weight of the body and absorb all of the loads imposed by the mechanical components and the terrain. The body contains and protects the cargo (everything contained by the body). Alternatively, the chassis can be constructed as an integrated frame and body, known as a monocoque. This is where the frame and body are combined into a singular, one-piece structure to perform both the aims of protecting the cargo and supporting and absorbing all loads imposed on the vehicle. The design of the chassis needs to strictly observe the Rules and Regulations of the FSAE, which will be referenced and checked off in this report when compared to the actual design of the chassis.
The main aims of the chassis, decided by the group, are to be to minimise the mass due to the majority of points in the FSAE Rules and Regulations being given to performance in the endurance race. This has been coupled with a financial viability. Even though these two aims appear to clash, with the generous budget of £40 000, the mass minimisation has been made the priority as long as the budget isn’t exceeded. Aerodynamics do play a role in racing car chassis design, however since the speeds being reached are not expected to exceed 80 mph and average speed around 55 mph it has been assumed that in depth optimisation of the chassis’ aerodynamics will result in minimal improvements to the performance other than trying to minimise the frontal area.
and Packaging