A number of companies are dropping wind tunnels in favor of virtual simulation. Against what people may think, the computer simulation gives a better idea of reality than wind tunnels.
Propulsion, also known as drag, has a complicated relationship with the speed of the vehicle. As the speed doubles the drag goes up to four times that much.
Using wind tunnels to test cars goes all the way back to 1960. Things that can be tested include the design, speed, fuel efficiency and how the driver handles the car, the latter is especially important in assisting racecar drivers to know how to perform in the toughest conditions.
For a car to turn corners at 200mph requires the aerodynamics to be tested and retested. Racecar designers will actually use wind to artificially increase the cars weight to improve its traction and handling. They do this by adding spoilers and fins in order to increase the downforce.
It’s important that the peak of the roof is far enough forward, which not only adds to the aerodynamics it means there is more headroom for the back seat.
BMWs are tested in the Aerodynamic Test Center, which recreated road speed and air speed, up to a massive 300 km/h. The difficulty here is that you need a prototype vehicle to start with.
The variables investigated include the drag, lift, side forces, pitch, yaw, and roll.
The lift is the opposite to the drag, an upward force countering the weight of the object.
The pitch is a rotation by side parts of the vehicle, it isn’t that noticeable unless you are talking about the wing of a plane or the sail of a yacht.
The yaw is the rotation of the vehicle’s nose whereas the roll is the rotation of the whole vehicle’s body, usually in a crash.
In reducing these variables, the car becomes easier to handle. To prevent a car skidding on the road, you need to know the yaw and the drag especially, to prevent the car flipping over you need to know the roll force, but also the load and pitch forces. Ultimately whatever happens to a car is a result of all these forces interacting with one another. If a car is unstable it will be harder to control.
The areas that are affected by the aerodynamics of a vehicle is known as a “flow field”. It all comes down to optimization, making the car as easy to handle as it can be. This include lengthening the car, which effects the flow field” to make the car more aerodynamic as well as fuel effective–the pressure is distributed around the vehicle. The “flow field” is a picture of the drag, lift and the side forces and is shaped in a similar way to the car itself.
After the indoor stuff the cars are tested on the racetrack. They require 200 hours in all.
Another way of carrying out test is modelling, at around 30-60% of the production size. It’s a way to carry out similar tests but to save on running costs.
It’s best to understand how your car operates in tests so you know where the potential liabilities are. A car only drives well because its aerodynamics have been well thought out.