The Diffuser Debate

2011 has seen many changes made by the FIA, both adding and banning certain aspects of the cars.  The biggest ban would be double deck diffusers.  When I first started this article, I will not lie. I had just a passing knowledge of exactly what a diffuser did for the teams and the cars.  All I cared to comprehend was that it was a large part of giving the cars more downforce and allowing the driver's a better handle on the cars whether it be on the long straights or in cornering.  

With the recent car launches, all eyes have been on what the teams have done to compensate for the ban of the double diffusers.

First launch and there were ideas of a new radical take on a blown diffuser from Lotus Renault GP. Renault R31 had a forward exhausts.  This season the exits are low down, just in front of the sidepods, in order to accelerate the airflow to the rear diffuser. They are angled backwards slightly, with a very long pipe length designed to minimise the torque and power handicap that comes with the unusual positioning. The Forward Facing Exhausts (FFE) which are placed to put a burst of hot exhaust gas at the sides of the underfloor area to act like an air curtain; increase low pressure seal effect (hence undercar downforce at speed), and increase air flow velocity to the diffuser out the rear and increase downforce a little there too.

What Lotus-Renault has done is basic.  They have taken the escaping exhaust flow and blowing it out through the sidepods between the chassis and radiators, then pointed it to the front edge of the floor. This accelerates the flow under the floor for more mass flow and hence more downforce.

Scuderia Toro Rosso launched their car on the first day of the Valencia test and were out to prove that they were no longer Red Bull's little brother but a force of their own.  Being a mid-pack team, most of their ingenuity has been over looked but their double floor arrangement is pure craftsmanship.Toro Rosso's 2011 car has raised sidepods to create a second venture channel in order to achieve extra downforce.  This separates the sidepod from the flat floor of the car to improve airflow towards the rear. 

Red Bull Racing and RB7's Diffuser. RBR appear to be working on a loophole in the new FIA regulations which allows a hole through the floor in the outer edges of the allowed Single Diffuser. They seem to be working on an Exhaust pipe outlet that exits just before this outer edge hole which must be above the floor level, but this floor hole itself has a forward facing upturned lip to grab the exhaust gas and direct it under the floor to feed the Diffuser below and generate some extra blown downforce. Blows into the out diffuser edge to create venturi low pressure. This arrangement is no-where near as effective as last 2 years Double Diffuser setups, but it is squeezing some more blown increase in back downforce.

RB7 with flattened exhausts reaching rearwards under carbon covers these reach towards the outer 5cm of floor and blow under the raised lip in the floor.  The fast moving exhaust gas then curves inside and blows out via the sidewall of the diffuser.  Blowing inside the  diffuser this way helps accelerate the airflow out of the diffuser and increases downforce.  As with last years EBDs they will be sensitive to throttle openings and Renault have assisted as much as possible in accommodating the aerodynamics with a special overrun strategy, to keep the exhausts gas velocity as high as possible without overheating the engine.

McLaren's MP4-26 and it's L-shaped sidepods. There is no doubting the new MP4-26 is very different from all the other 2011 cars. Technical director Paddy Lowe has exploited to the extreme the idea of higher outer sidepods. The aim is to clean up and better direct the airflow to the beam wing at the rear of the car, an area now even more important thanks to the ban on double diffusers. This solution also gives McLaren the possibility of running Renault-style forward exhaust exits.  What the team have done is to shift the inlet for the radiators at the front of the sidepod as far outboard as possible, to allow a freer flow of air to the rear beam wing.  With the double diffuser banned, a larger proportion of rear downforce will have to come the from the rear wing.


Glossary

Diffusers 
Are essentially a raised area at the back of a car. In order to maximize the effectiveness of a diffuser, a car has to be run as low to the ground as possible. This causes the air trapped between the car and the ground to move rapidly to the rear. The diffuser section in the rear causes negative pressure at the back of the car because it has a bigger volume than the area that the air flowing into it is coming from. This negative pressure accelerates the air under the car which puts the whole underside of the car under negative air pressure. This creates a vacuum effect under the car which sucks it into the ground and creates downforce.


Downforce
Is a downwards thrust created by the aerodynamic characteristics of a car. The purpose of downforce is to allow a car to travel faster through a corner by increasing the vertical force on the tires, thus creating more grip.


Double Diffuser
(See Diffuser)Allowing for more volume in the diffuser, holes in the underbody, perpendicular to the reference plane (not visible as a hole when viewed from directly above), that fed a diffuser channel that was above the main diffuser. This greatly increased the available downforce, and was worth about half a second per lap.

Sidepods

Bodywork on the side of the car covering the radiators and engine exhaust. Aids in engine cooling, car aerodynamics and driver protection in the event of a side impact.