Restrictions on aerodynamic testing
Aerodynamic resource restrictions in Formula One were introduced in 2009 as a means to limit a team’s expenditure on aerodynamics. Large investments were being made in full-scale wind tunnels, computational clusters and on-track testing – investment that was getting out of control. To prevent an ‘arms race’, running full-size cars in a wind tunnel (WT), and track testing, were severely restricted. In addition, limits were placed on a team’s wind tunnel and CFD usage.
The restrictions were introduced by FOTA, with the teams having to submit a declaration at the end of each testing period summarising the resources used. There are two principle measures:
- WT wind-on hours per week. This is the length of time the WT is switched on, with the speed above a nominal value. The longer the WT is running for, the more parts that can be tested, or the more data points that can be sampled for each part.
- Average CFD teraflops. This is a measure of the computational usage of a CFD cluster. For a given cluster and CFD model, the more teraflops that are available, the more CFD runs/geometry changes that can be made.
These measurements are averaged over eight-week periods, so teams typically own CFD clusters that have a peak capacity rated as significantly faster than the restrictions. This allows them to cope with periods of high demand, as long as they operate at reduced capacity later on in the eight-week cycle.
New restrictions for 2014
For 2014, the testing restrictions are now an appendix to the sporting regulations, and are enforceable by the FIA; they are no longer optional or as open to abuse. Beyond this, the two main changes for 2014 are:
- A reduction in the WT and CFD limits to 30 hours and 30 teraflops (see Fig. 1).
- The number of WT runs is limited to 80, and occupancy time is restricted to 60 hours (the length of time a model can be installed in the WT, having parts changed or ready to be tested)
It is the limit on the number of WT runs that is incredibly restrictive, rather than the reduction to ‘30/30’. A Formula One wind tunnel will typically run for close to 24 hours a day, six or seven days a week, during which it can perform upwards of 200 runs, so the new restriction cuts this down to roughly a third of the current run rate. Assuming that each WT run is testing a new part, this is a dramatic reduction in the number of components that can be tested in the tunnel.
Implications of the new restrictions
With fewer parts being tested in the WT, the development rate is likely to drop. One way to counteract the reduction in the number of parts tested would be to test each part for longer, sampling more detailed data. However, occupancy limits will limit this, as it works out to be only 45 minutes per run, which must include the time taken to change parts on the model.
The reduction in WT testing could also lead to a greater emphasis on the use of CFD in the development process. Designing parts in CFD prior to tunnel testing allows all but the most promising directions to be filtered out without wasting tunnel runs and time.
General implications of aero restrictions
While restrictions on aerodynamic testing make sense from a financial point of view, particularly in the field of CFD, they have also removed a lot of the industrial relevance. In the past, the needs of Formula One have pushed CFD developments forwards, and this has led to faster clusters along with faster and more efficient CFD software for the wider community. The recent restrictions have led Formula One teams to put major resources into tailoring their individual CFD process to provide the highest throughput for their limited computational capacity, but most of these optimisations have no relevance in the wider industry, which can now call on greater computing power than in Formula One. Also, other promising CFD simulation techniques that are gaining traction in industry, such as design of experiments or design optimisation, are no longer viable in Formula One owing to their large computing requirements.
Fig. 1 - Aerodynamic resource restrictions (Source: FIA 2014 Formula One sporting regulations)
Written by Matt Layton