this is your ultimate tool,’ highlights Andreas Kremheller, Aerodynamicist at NTCE. ‘The sooner you can utilise that tool to shape your vehicle, then surely that minimises the risk as you are already using that tool to develop your vehicle, rather than a coast down test.’
Another point to note is that as hybridisation in our cars continues to grow, phenomenon’s such as Wind Noise will have a larger impact on the cabin comfort of these quieter vehicles.
Therefore, companies will have to invest more into methods to help reduce Wind Noise, which includes Wind Tunnel testing.
In summary, Wind Tunnels have a bright future, as both motorsport and automotive companies will continue to utilise them, even if it is not a 100% accurate method, it remains the closest thing to reality. Especially when both the regulations and companies keep pushing to reduce costs and consequently the amount of physical testing will continue to diminish to a minimum.
Improving the Correlation
With the delta between CFD and Wind Tunnel remaining an issue, technologies have been developed to help improve this correlation. One of which is Particle Image Velocimetry (PIV) systems which helps visualise the flow using tracer particles that are illuminated in the flow and thus the instantaneous velocity and other fluid properties can be measured.
‘We have real time autonomous PIV systems, so when the engineer wants to deploy them they take data live slices during a physical run. This means that even before the run has finished you have the correlation delta between the CFD plane and the plane in the Wind Tunnel run which completely transforms the way you can operate,’ explains Prof Mark Gillan, Director of Motorsports Technology Group at MTS.
‘Recently the importance of visualisation in the Wind Tunnel has come on leaps and bounds. In the mid 2000’s using PIV systems was difficult and time consuming, but now you can achieve robust real time analysis fully autonomously. PIV really is game changing particularly for doing correlation work. That is why you see F1 cars during testing running with these half metre square rigs as this is the plane that they can measure on the PIV systems.’
The Regulations Role
In Formula One, the regulations have changed dramatically over the last 5 years in terms of Wind Tunnel testing to try and reduce costs. Now, the Wind Tunnel model is a 60% scale model, the air speed is limited to 50m/s at atmospheric pressure, only 65 runs can be completed within a week utilising 60 hours of tunnel occupancy per week.
‘In Formula One before the rule changes, aerodynamics and CFD were two completely different worlds. At that time it was Wind Tunnel dominated because teams had larger budgets and no restriction on tunnel time so we were throwing money at Wind Tunnel testing, hoping to get a good result without really understanding what we were doing,’ highlights Franck Sanchez, Principal Aerodynamicist, Scuderia Toro Rosso.
‘Now with the regulation changes, we had to completely re-think our whole process. CFD became more important and mainly used to establish the next steps in our development process and of course, Wind Tunnel correlation became critical and we spent a large amount of our Wind Tunnel runs on correlation studies.’
If you take all the testing runs and resources an F1 team is now allowed for aerodynamic and split it between CFD and the Wind Tunnel that gives you around 12.5 Teraflops of CFD and 12.5 ‘wind on’ hours in the Wind Tunnel per week.
Compare this with what was allowed in 2013, and as you can see on the graph Wind Tunnel time has reduced by a huge 70%, which now means that each Wind Tunnel run can only last 11.5 minutes. ‘We just had to adapt,’ continues Sanchez, ‘at the time it was not good, but looking back, it actually pushed us to become better aerodynamicists.’
Mark Gillan agrees from his past experiences in F1; ‘In 2008 when I was at Toyota we were blessed with having two Wind Tunnels operating 24 hours a day, 7 days a week. However, when the restriction came in, it was not a good thing because people lost jobs, but it did make us stop and think about what we were actually doing. Within three months we had effectively reduced to two shifts in the two tunnels and in actual fact we were obtaining more data and information than before because we had invested in technologies such as continuous motion systems and high speed acquisition.’
Although the main aim of the restrictions was to reduce costs, which arguably it didn’t as teams just invested their money into other areas such as CFD, the new rules actually advanced the development of aerodynamic testing. Furthermore, because of the sudden reduction in resources CFD and Wind Tunnel engineers had to work together, which increased development rates further. ‘The increased restriction in Wind Tunnel time now means that there is less distinction between experimental aerodynamicists and CFD aerodynamicists,’ highlights Franck. ‘They are now both doing a very similar job. Both Wind Tunnel and CFD are complimentary tools and I don’t see how we could only use one of them.’
From 2013, the Wind Tunnel time has been reduced by 70% by the new rules (assuming a 50% split in resources between CFD and Wind Tunnel); forcing aerodynamicists to optimise their processes.