The Aerodynamics of Overtaking – Part 2

We compared the aerodynamic performance of two generations of F1 car under overtaking conditions in Part 1 of this blog.

When following a lead car, we witnessed how modern F1 vehicles lost a significant amount of downforce, particularly from the front wing. In Part 2, we’ll look in greater depth at why this happens and also explain why older generation cars did not experience similar losses.

We’ll begin by considering the lead car moving along the race track.  This car will impact and interact with the air as it travels along, imparting momentum as it does so.  The previously stationary air is pushed forward with the car as well as being thrown upwards (and outwards and around in circles!).

Newton’s Third Law tells us that “every action has an equal and opposite reaction”.  So, as the air is pushed forward, the car is pushed back (a.k.a. drag) and as the air is thrown up, the car is pushed down (a.k.a. downforce).

The body of disturbed air that trails along behind the lead car is known as its ‘wake’.  When a following car enters the wake it will experience a loss in both drag and downforce.

This occurs because the air in the wake of the car is already moving forward, reducing the speed differential between the air and the car. As a result, the car will transmit less momentum to the air, resulting in less push back (drag) and less push down (downforce).

The amount of downforce generated by the following car’s front wing will be reduced by the lead car’s wake, as we know. Why does the modern-era SF16’s wake impact its following car more than the F312? To answer that, we need to look at the size and shape of their wakes.

The image below left shows our SF16 model in the ’10m offset’ configuration. The arrangement is the same in the adjacent shot, except the lead car’s wake is displayed in blue (in fact this is an iso-surface of constant total pressure). The following car is completely engulfed in the wake, as you can see.

The comparable images for the F312 are shown below. If you look closely, you can see that the front wing of the following car is still visible in this scenario. This means the front wing will be working in ‘clean air,’ or air that hasn’t been disturbed (or, more likely, has been less affected) by the lead car. As a result, it loses less performance than the wing of the SF16.

The two images below show a cross section of the lead cars’ wakes. This more clearly shows how the SF16 has a much wider wake that encompasses the front wing of the following vehicle. By contrast, the F312 is only impacted down the car’s centreline.

To be continued...

We now understand why the performance of the SF16 is impacted more than the F312. However, the question remains, why do the cars have such different wake structures. We’ll take a look at this in the final part of this series.

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