F1 aerodynamics- adverse effects on overtaking?!

Formula One racing has recently come under scrutiny due to a lack of overtaking, and rules are constantly being changed in an effort to reduce speeds and increase overtaking. The lack of overtaking was conspicuous by its absence at Silverstone this week as this track is known to be one of the best tracks for overtaking as it provides wide roads and the fast sweeping corners.
Aerodynamics plays a big part in the problems of overtaking, and since the introduction of aerodynamic principles into Formula One, they have become of ever increasing importance to the car's performance. The aerodynamic requirements of the F1 car are high downforce at minimum drag - but the more downforce you have, the more drag you incur. This drag is due to air being disturbed as it flows over the vehicle, and as the air does not have the energy to sort itself out, it ends up following the car as its wake.
In an F1 car all the aerodynamic devices are so close together that there are large interactions, and the rear wing, rear wheels and floor-level diffuser contribute significantly to the shape of the wake. As the air travels over the car, it will lose energy, and cannot return to its initial values of speed and pressure, and this is what the wake is.
Any vehicle which produces lift (be it positive in most road cars, or negative in racing cars) will produce vortices - the phenomenon you see when water swirls down a plug hole. The F1 rear wing, for instance, will produce a significantly large pair of strong vortices called trailing vortices which last a large distance behind the wing which created them. There are often seen as swirls of white on the edges of the rear wing when the air is moist. In an F1 car, they rotate in such a way as to produce an upwash (air travelling rearwards and up relative to the ground. In addition to this, the flow underneath the car plays a large part in the shape of the wake. The F.I.A. Regulations state the major percentage of the car floor must be flat, but diffusers are allowed. The air channels out of the diffuser and is immediately sucked upwards due to the influence of the rear wing, adding to the already large upwash in the centre of the wake, which creates a low pressure in that area. As the wake moves with the car, this causes a drag upon it, and will also cause problems for the vehicle behind.
The effect on the following car is beneficial in a straight line as it will get a 'tow' from the car in front, and its drag will be reduced by following in this turbulent air. Drivers say the 'tow' from the low pressure wakes (often referred to as a slipstream) can be felt up to six car lengths behind, but it is only significantly large when trailing by approximately one to two car lengths. However, it has been suggested that tows from older F1 cars were larger (which makes sense, as they had more downforce), and this is one problem suggested for the lack of overtaking in present day Formula One. Down a straight, a bigger tow makes it easier to close on the car ahead, and if you have less tow, it is harder to get close to the car at the end of the straight when you are coming into the corner, so harder to get into a good position to overtake.

In cornering, however, the effect of the wake is very detrimental, and drivers complain of understeer (brought about by a loss of downforce due to wake effects) up to three or four car lengths behind. The car's downforce decreases because the air the car (especially the front wing) is working in has less energy than normal, and the air separated from the wing surfaces earlier than normal. The car cannot sustain wheel side forces similar to the car ahead, so cannot travel as fast through the corner. It will therefore drop back and not be in a position to overtake once on the straight - another aerodynamic problem once again giving the upper hand to the car in front (not the best plan if overtaking is required!).
In simple terms, if one car follows another closely at high speed, the front car punches a hole in the air, allowing the second car to travel at the same speed while using less engine power and it is thus able to pull out of the slipstream, apply more power and overtake. However, the complex aerodynamics on an F1 car means that the following car’s balance is upset by this and either cannot get close enough to pass, or loses downforce which can lead to loss of grip and a crash.Air on the car creates dynamic pressure and if there is a car in front of you, it has two effects. The air on the car is reduced and so the car generates less downforce and the air coming towards you is not "clean" it is turbulent (sometimes referred to as ‘dirty air’). Cars do not like that. As a car closes to the one in front, the following car loses more downforce because of the turbulence of the air and there is an upwash from the car in front so air hits the car from an angle it is not designed to deal with