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The image above highlights the main vortical structures (swirling flow) generated by the front wing. Aerodynamicts will meticulously optimise the vortex strength, placement, and interaction with one another to manipuate the flow around the rest of the car. Vortex flow management is now one of the key aspects in designing a successful Formula 1 car. For this visual, streamlines (the path that a particular fluid parcel travels along) are released within the vortex core and traced upstream and downstream. These streamlines are coloured by velocity where red indicates fast moving flow and blue indicates slow moving flow.
This is the second of a series of blog posts about F1 aerodynamics and follows on from the article titled Secrets of a Formula 1 Front Wing.
Why Downforce Matters
In the late sixties, the first aerodynamic revolution in race car design had arguably occurred. Prior to this period, early aerodynamicists focused primarily on streamlining the bodywork to increase top speeds. This was partly driven by the nature of historical race tracks which were generally characterised by very long straights. Racing cars in this era are geometrically recognisable by their long and narrow ‘bullet’ shaped bodywork (as well as their tall and slender wheels). However, it soon became apparent that aerodynamic influences were affecting the stability of the car at high speed (the cars were in fact generating lift).
As racing tracks began to shorten and the complexity of circuits increased, it was soon discovered that the limiting factor in determining the performance of a racing car was its acceleration rather than its top speed. In other words, it was the rate of change of velocity that mattered. If a car could accelerate quicker, change direction faster and/or brake harder, then the average speed of the car over a single lap will increase and hence the overall lap time will be reduced. Thus, towards the end of the sixties, the primary focus had shifted from drag reduction to downforce generation. An aerodynamic proliferation of innovative inverted wings began to spread and the era of downforce generation had begun.
Over the next 50 years, a downforce driven design process has sculptured the shape of the modern Formula 1 car. The role of downforce is to augment the acceleration of the car, a catalyst to elevate the performance to a higher level. The greater the downforce, the greater the frictional forces between the tyres and the ground. This leads to an increase in traction which permits the car to accelerate, decelerate and corner quicker. Downforce increases the weight of the car but without increasing the mass of the car.
Downforce Generating Components
There are four main components each contributing to the generation of downforce. These are the front wing, underfloor, diffuser and rear wing (the bodywork actually generates lift). The front wing is typically responsible for 25% of overall downforce levels whilst the rear wing also accounts for 25%. The remaining 50% is generated by the underfloor and diffuser combination. Each component has been specifically designed to work in conjunction with one another. Hence a front wing that works effectively on one car, may not necessarily work on another. Therefore one of the biggest challenges in race car design is to develop a synergistic set of components that maximises the performance of the car.
The image above shows the static pressure distribution on the surface of the car. Orange to red indicates positive static pressure exerted on the surface (i.e pushes into the surface of the car). Green to blue indicates negative static pressure exerted on the surface (i.e pulls at the surface of the car). The majoirty of downforce generation occurs on the lower ground facing surfaces.
The Importance of Aerodynamic Balance
A visual representation highlighting the magnitude and distribution of vertical forces generated by a Formula 1 car. Blue to pink represents increasing downforce generation whilst green to red represents increasing lift generation. Critical downforce generating components can be clearly be seen, these are the front wing, underfloor, diffuser and rear wing. Notice how the downforce is distributed at the front, middle and rear of the car. This results in a relatively even distribution of load between the front and rear tyres. For this visualisation, the forces are integrated in the direction of the view (i.e forces are summed between upper and lower surfaces – this is essentially ‘adding’ the two images in figure 6 together but also includes internal surface).
Shortly after the introduction of aerodynamic wings in Formula 1, it quickly became apparent that the distribution in downforce was critical in determining the handling characteristics of the car. If too much rear downforce is generated, then the front end will lack grip and the car will tend to understeer (front tyres will slip). Conversely, if too much front downforce is generated, then the rear end will lack grip and the car will tend to oversteer (rear tyres will slip). A front and rear wing combination was quickly established such that the aerodynamic forces were evenly distributed between all four tyres. Typically, a race car is setup in such a way that the centre of pressure (i.e the location of the resultant aerodynamic forces) acts behind the centre of gravity. For a mid-engine race car, this typically means a greater proportion of the downforce is desirable at the rear. For a Formula 1 car, a typical aero balance number (% of total downforce acting at the front wheel axle line) is approximately 45%.
The image above shows the typical downforce distribution level between front and rear axle lines for a Formula 1 car.
The next article in the series will be focused upon the front wing. Follow us on twitter, facebook or LinkedIn to be the first to read.