Ferrari have admitted that they need to re-design the sidepods on their 2012 Formula 1 car to take full advantage of the exhaust-blown effects still available within the current regulations. In fact, the re-design will be sufficiently radical to require a new side-impact crash-test.
So why exactly can't Ferrari just modify their existing sidepods? Mark Hughes explains in this week's Autosport that Ferrari need to move their exhaust exits further forward, thereby requiring a re-arrangement of the sidepod internals.
However, there's perhaps something else here which hasn't received much attention. Ferrari's original sidepods combined the radiator cooling exits with the exhaust outlets, whereas the trend on other cars such as the Red Bull and McLaren, is to separate the two, with a single cooling exit placed at base of the engine cover in the centre of the car.
The idea of having the cooling exit duct co-axial with the exhaust outlet was very popular in the early 2000s, and the reason is that the flow of exhaust gases can be used the increase the mass-flow rate through the cooling system, a phenomenon sometimes referred to as 'aspiration'. If you pull the flow out of the cooling system more quickly, you can get the same mass-flow rate for a smaller inlet area, and a smaller inlet provides aerodynamic benefits. This concept was studied by Parra and Kontis in their 2006 paper, Aerodynamic effectiveness of the flow of exhaust gases in a generic formula one car configuration, published in the The Aeronautical Journal:
"Due to the characteristic configuration of a Formula One car, the exhaust pipes pass through the chamber located directly behind the radiators. This chamber is normally shaped so that it enhances the outflow of gases. However, an extra outflow could be generated by inserting the exhaust pipe into a bigger diameter duct to create a mixing stream. Such mixing is believed to generate an aspiration along the outer duct, based on the same principles of operation as an ejector pump. Because this enveloping duct connects the chamber behind the radiator with the atmosphere, an outflow of gases through this passage would increase the efficiency of the radiator," (p574).
The exhaust outlet on Ferrari's original 2012 sidepod was inside the cooling exit duct, which in turn, was inside a downwardly-inclined funnel at the rear of the sidepods. Thus, Ferrari's original 2012 solution was perhaps a very neat idea: they might have been trying to use the exhaust gas to aspirate the cooling flow, and simultaneously use both the internal cooling flow and the external sidepod flow to pull the exhaust jet downwards.
However, once this failed to achieve the desired exhaust-blown effect, it became necessary to separate the exhaust outlet from the cooling outlet, as seen in testing at Barcelona (pictured). Once the exhaust outlet is separated from the cooling outlet, the mass-flow through the cooling system is no longer aspirated by the exhaust, and it may now be necessary for Ferrari to design a sidepod with a larger cooling inlet, as well as one which brings the exhaust outlet further forwards.
Moreover, with a reduced mass-flow through the radiators, it may be necessary in the interim for Ferrari to turn their engines down slightly, and Stefano Domenicali confirmed in Melbourne that "the car at the moment is slow in a straight line."