Aerodynamics of cars

Aerodynamics of cars

Introduction

Aerodynamics is the learning of the interaction between bodies that are moving and the fluids that surround them, through them and under. It was first discovered by aeronautical engineers who were studying aircraft wing designs that fly within the atmosphere. The advantage of aerodynamics has made it possible to invent new things, which include the design of the automobile and bridge design. The problem that aerodynamics is trying to solve is to reduce wind noise and Drag, minimize noise emission and prevent lift force, which is undesirable and other factors that can cause instability of aerodynamics when at high speed. In this case, the air is considered fluid. In areas of cars racing, it is crucial to make a downforce, which will help in making traction better and cornering abilities. The types of fluids that are used in aerodynamics are air and water.

Essentially, when one has a car that is constructed with airflow in mind, that will make it have less difficulty while accelerating and thus make the care achieve fuel save since the engine lacks resistance from the air. What the engineers have done is that they have made designs that are rounded, and exterior shapes are crafted to channel the air around the car with minimal resistance (Vdovin, 2013). Others have opted for the spoiler to make sure the air does not lift the wheels of the car and making it become unstable while at high speed. Important forces that are in aerodynamics are Drag and lift forces.

Drag

The force aerodynamics drag is one that opposes the movement direction of vehicles. High speed is the main contributor to drag, which acts on the surface friction, the surface of the vehicle, and the pressure which is left behind the care, which is negatively relative. Drag increases with a velocity, which means the faster the car moves, the more the Drag it experiences.

Mathematical formula for getting aerodynamic drag is

D= CD 1/2PV²A  Where;

D = Drag Force N

CD = Drag Coefficient

½ = Mathematical Constants

ρ = Air Density Kg/m3

V2 = Speed m/s

A = Frontal Area m2

Through the law of Newton’s, we can measure the object motion. The parameters that we use include weight, mass, velocity, acceleration, and external force. Drag has a direct acceleration effect, which means acceleration of a car its weight minus the Drag, which is divided by its mass (Kitagawa, 2002). During acceleration, object drag and velocity also increase up to that point where Drag is the same as the weight; in this case, there would be no further acceleration happening. That means when the Cd is lower; then the vehicle can move easier through the air.

Lift

This is a force that occurs perpendicular to the motion of the vehicle. It is important for automobiles, such as the aircraft, to make a positive lift to make them fly, but this is not necessary for motorsports (Hassan, 2014). What the motorsports do is that negative lift is sought after to make the vehicle to stick to the ground, the advantage of this force is that it helps increase the grip of the vehicle which leads to a faster speed of cornering. The mathematical formula for this lift force is almost the same as that of drag force, but the drag coefficient is replaced with the coefficient of lift as shown

L =Cl ½ pv²A

L = lift N

CL = lift coefficient

A = frontal area (vehicle) plan area m²

Analysis

BMW z4 is the car we will focus on in the analysis; it has a drag coefficient of 0.34, and the area front of the drag coefficient is of ration 0.65.

Concept modeling

It was designed using the dimension basic and BMW Z4 canvas images. The preferred software was Autodesk alias speed from 2016, which is a package for industry surface modeling.

The rendering image of the BMW Z4 with the wheel designed in Autodesk inventor is as shown below.

Initial testing took place using CD-Adapco’s star CCM+ computational fluid dynamic software. The test was carried out at 120kph, and the tunnel wind was measuring 65m in length, 10m high and 10m wide. The density of air was 1.2255kg/m^3.

Analysis result

The initial testing was done using the formula;

Weight force (kg) = force/ gravity

From the analysis result, there is an unwanted lift in the car, which can lead to handling characteristics that are undesirable, for instance, understeer. The contributors are slow air velocity beneath the vehicle, which results in the pressure area is high, causing the car upwards. The other is the high-velocity air that passes over the roof, which results in low pressure passing over the vehicle; the low area pressure pulls the car upwards, creating lift.

The biggest contributor to the Drag of the vehicle is a large, slow turbulent speed air area behind the car that tries to pull the vehicle reverse. Another area that brings Drag is the flow separation area, which is at the bottom of the windscreen and rear window. The flow separation brings turbulence on the vehicle surface, also within this area of separation, the air velocity becomes zero.

Conclusion

The principle of aerodynamics has been researched and used on CFD area simulations of data. A concept vehicle was established using the industry surface standard modeling software, then modified successfully to increase the downforce of the vehicle. After that, it was seen that downfall and Drag would hike the consumption of fuel by increasing the drag coefficient and the resistance of rolling.

Reference

Kitagawa, T., & Nagakura, K. (2000). Aerodynamic noise generated by Shinkansen cars. Journal of Sound and Vibration, 231(3), 913-924.

Hassan, S. R., Islam, T., Ali, M., & Islam, M. Q. (2014). Numerical study on aerodynamic drag reduction of racing cars. Procedia Engineering, 90(January), 308-313.

Vdovin, A. (2013). Investigation of aerodynamic resistance of rotating wheels on passenger cars.