Aluminum Wide Bodies, Oversized Spoilers, Ducts, Vents and more Vents, Splitters, Canards and Diffusers. How do they fit into the bigger scheme of things and what do these modifications hope to accomplish? We will address these issues here as best we can. First, a little understanding of the Bernoulli Principle is essential to gain insight into matters regarding aerodynamics. We will attempt to address this very critical fundamental of fluid dynamics in a manner that is easy to comprehend.
Bernoulli's Principle works on the premise that faster air travelling along a surface will have a lower static pressure than slower air. With reference to the illustration below, the air flowing along the upper surface is travelling faster than that found at the bottom. The air is forced around the contoured surface, thereby travelling a greater distance within the same amount of time, hence the increased speed. This phenomenon is known as lift and is the basis behind airplane flight.
For vehicles that are grounded however, too much lift creates instability as there is reduced traction between wheels and asphalt that ultimately results in diminished cornering performance. All production cars, except those that hail from racing pedigrees like the Ferrari 430 and the Koenigsegg CCR, are subject to the adverse effects of excess lift.
Car owners that take their vehicle's cornering capabilities to the limits, would be wise to invest in enhancements that will generate downforce. Essentially, downforce is lift reversed. A simple inverted wing shaped spoiler does just that. Wings on an airplane enable them to fly and an inverted wing spoiler on the boot of a vehicle will, if the spoiler is in contact with the clean airflow at the rear of the vehicle, generate downforce imparting improved handling characteristics to the vehicle. If the downforce generated by the spoiler is still insufficient, a simple right-angled piece of metal called a gurney flap, when attached to the trailing edge of the spoiler, can and often will augment the spoiler generated downforce by up to 25%.
Spoiler with trailing white Gurney Flap
Splitters and air dams also seek to provide an element of downforce and added stability to a vehicle. Essentially splitters are spoilers mounted beneath the bumper and they are shaped to reduce the airflow beneath the vehicle by 'splitting' the high-pressure zone from the low-pressure high-speed flow. With lower pressure beneath the chassis of the vehicle comes a suction effect that facilitates the speeding up of air below the vehicle. Less air at greater speeds beneath the chassis translates into less pressure, thereby diminishing the pressure gradient between the upper and lower surfaces of the vehicle, hence the decreased lift. Air dams operate differently from splitters yet utilize the same concept. Air dams are vertical barriers that reduces the size of the opening leading to the bottom of vehicles. Their purpose is generally to block turbulent air and reduce drag underneath the chassis of the vehicle.
Splitter & Air Dam
Canards are airfoils that are mounted on the front of the vehicle. Canards generally produce a limited amount of downforce by virtue of their shape and orientation. By directing the airflow upwards, a slight gain in frontal downforce can be realized. Canards also act to generate strong vortices along the sides which limit the amount of high-pressure air that enters the undercarriage, thereby enhancing the downforce characteristics of the vehicle. Nevertheless, the vortices contribute significantly to drag and thus canards are more suited for tuning aerodynamic characteristics, rather than utilized as an instant downforce fix.
A variety of Canards at the Super GT Series
Diffusers are extremely effective in reducing turbulence and increasing downforce. Rear diffusers work by facilitating the flow of undercarriage air into the wake region. The wake region is essentially a vacuum created when the vehicle displaces air and creates a perpetual low-pressure area directly behind the vehicle, as air does not have sufficient time to rush in to fill the vacuum. This phenomenon is known as flow detachment and contributes to instability. As diffusers slope upwards and for all intents and purposes create a larger aperture for airflow to exit the undercarriage area, the air is slowed down and reintroduced into the wake area more efficiently. Many such enhancements have vertical vanes that further enhance flow.
F430 Rear Diffuser
Lower-pressure air that enters through the front, when aerodynamic enhancements are used, will create a vacuum effect in the undercarriage that will suck in the higher-pressure airflow from the sides. Side skirts are used to reduce airflow entering the undercarriage from the sides thereby increasing downforce, facilitating flow attachment, and reducing turbulence in the undercarriage region.
Celica (ARS-G3) Side Ducts
The primary purpose for having fenders with side ducts is to maximize brake and engine bay cooling. Well designed front undercarriage diffusers will direct the flow to the rear of the front wheel wells. When side ducts are used, flow is enhanced as the ducts direct the exit of hot turbulent air through the sides instead of outwards through the turbulent vortex areas generated by canards. With better flow, engine bay and brake cooling is very much aided resulting in better performance, and a decrease in drag.
There is a trade-off between improved cornering capabilites and additional drag that must be addressed. With downforce comes induced drag, as the resistance the vehicle needs to overcome is increased when downforce is increased. Drag reduces top speed but will allow faster cornering. Racers also witness a tendency for cars to understeer should there be excessive downforce in the rear region of the vehicle. Therefore an optimal balance sought between the two aerodynamic factors is fundamental to faster lap times.
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