Mysteries of the vapour trail revealed

The United States and Brazilian Grands Prix bring down the curtain on this technical era of Formula 1 and represent the last hurrah for the raucous, high-revving 2.4-litre V8 engines and the current aerodynamic rules.

With such far-reaching changes looming, development of the current cars has tailed off for all but a few teams and most of the past two weekends has been dedicated to the 2014 season.

The grey line shows the vortex path.

VAPOUR TRAILS

Much of the aerodynamic analysis in AUTOSPORT's technical features talks not about parts creating downforce in their own right, but about generating vortices to influence the flow downstream.

Such talk tends to be somewhat esoteric because we can't see the airflow and can't be sure where it goes. But footage from the past two race weekends has clearly shown at least one of these phenomenon, the Y250 vortex.

Trailing from the Red Bulls and the Ferraris, a tightly-formed spiralling vapour trail could be seen to emerge from the front wing, pass along the car, turn around the sidepods and disappear before the rear tyres. Unlike the vapour trails seen spiralling from the rear wing tips, this vortex is created for a very specific purpose.

The rear wing vortices are unwanted as they reveal how the wing is creating drag. Teams spend a lot of time trying to reduce this effect from the rear wing to boost straightline speed.

The Y250 vortex is created on purpose and although it does have unwanted effect by creating regions of low pressure and drag, its net effect is positive.

Red Bull's complex front wing

This is far from the only vortex flow structure on the car. There are dozens created all over each and every F1 machine. This isn't something unique to Red Bull or Ferrari.

At the point where the front wing meets the mandatory neutral centre section, the intersection is shaped with a subtle arch. This point is 250mm from the car's centreline, and gives the flow its name from the position where it is formed on the car.

This sets off the corkscrew-shaped airflow in which air is concentrated into this tightly twisting formation. Like a tornado, it is very powerful. The moisture in the air condenses inside the vortex, creating the vapour trail, which is visible on damp days. Teams will direct these vortices for a beneficial effect elsewhere along the car.

In the case of the Y250 vortex, the flow is used as a virtual turning vane. The power of the vortex is used to direct the advantageous airflow towards the floor's leading edge, which boosts downforce from the underbody.

Meanwhile, the vortex also keeps the front tyre wake away from the car's bodywork, again aiding the efficiency of the car's aero surfaces in the face of the turbulent air generated by the wheels.

The path of the vortex can be seen to turn quite abruptly in front of the sidepods. The physical turning vanes and sidepod vanes help to bend the trail around the car. By the time the turn has been completed and the vortex is passing along the sidepods, its effect is over and it breaks up and passes around the rear tyres.

This far back there isn't any direct benefit being created, but turbulence is still created by the flow. This helps to disrupt the aero of the following car. This isn't an effect designed into the Y250 flow structure, simply a coincidental side benefit.

OTHER AUSTIN AND INTERLAGOS UPGRADES

FERRARI FRONT WING

Ferrari's revised front wing © autosport.com

Amid the battle for second in the constructors' championship, Ferrari took a revised front wing element to Austin. The smaller inner cascade fitted above the main front wing was split into three elements.

As explained in the Y250 section above, this element does not function as a wing, but as a vortex generator.

In the case of this little inner winglet, the trails lead upwards and over the front tyre. The aim is to negate the unwanted vortices produced by the spinning tyre and the area of turbulence behind the tyre.

Splitting the winglet into more sections creates a finer control of the vortex and hence more accurately offsets the negative effects of the front tyre wake.

LOTUS FLOOR SLOTS

Lotus introduced a new detail around the floor in front of the rear tyres. The metal floor section now has three slots machined into it.

These work along similar lines to the front wing cascades, in that they offset the negative effect of the turbulence created by the large rear wheels.

Lotus added more detail to the floor © autosport.com

Known as tyre squirt slots, these offset the airflow that spills off the inner shoulder of the rear tyre, squirts inwards and interferes with the flow through the diffuser.

The higher pressure air passing from above the floor passes through the slots and blows the tyre squirt away from the diffuser.

As much as we call these slots, according to the rules they must not be enclosed holes. So the team creates a tiny gap between them and the edge of the floor.

Exploiting this loophole means they can act as enclosed hole in the floor, despite the thin joint to the floor's periphery.