Pre-2009, it was fairly uncommon to see the cars covered in Flow Visualisation Paint (or Flo-Viz). However McLaren were in a spot of bother with their MP4-24 and were taking every measure to raise their competitiveness and I distinctly remember the brightly coloured stuff plastered over the car numerous times in winter testing. Since then flo-viz has been a common feature during testing and even during free practice on a Grand Prix weekend. This boils down to the fact that testing is limited and – with the car’s aerodynamics becoming evermore complex – analysis of exactly how airflow is behaving as the car goes round on track is essential to development.
We hear a lot about wind-tunnel correlation and teams complaining that their car is not performing as it should compared to the figures they produce in the factory, and these statements are all very relevant in today’s formula. Although some wind-tunnels allow some degree of artificial pitch and yaw movements, most teams will be testing their scale models in a straight line to oncoming airflow. They can turn the wheels to the airflow in a bid to understand airflow behaviour during a corner, but you then have to take into account the load on the tyre, the sidewall compression, bumps, tiny driver inputs, air temperature… The list goes on! So what’s the best tool for on-track aerodynamic measurements? Pitot tubes quite possibly, but a flo-viz is another brilliant method.
So what exactly is flo-viz? Its main component is paraffin (kerosene) and fluorescent powder is suspended within it. Paraffin is a very light, clear oil and whilst its flammable properties are similar to that of diesel, you may notice that the teams tend to keep it well away from the exhaust! The teams will apply the mixture with a paint brush or spray gun in the areas they want to examine. Flo-viz can be applied in very small amounts to assess regions of the car that they may not want the opposition to see or across large areas of bodywork. Red Bull often put a smattering on the tyres too, just for good measure.
The car is then sent out around the circuit for a lap before immediately pitting. During this time the paraffin base will have spread across the bodywork under the influence of airflow and the fluorescent powder shows its path. Flo-viz doesn’t dry as such, but it will stay in its position after the car has stopped and is wheeled back into the garage. The mechanics/engineers will then take pictures of the bodywork which will then be sent back to the aerodynamicists at the factory for further analysis.
The teams can also choose to carry out work on-site if they see an area that may need changing. For example if a new rear wing arrives and they aren’t sure if it will work better than the old wing, they can run flo-viz over both and check for any signs of airflow detachment of flow imperfections. Detachments are identified by areas where only small amounts of flo-viz have passed over the surface, or even failed to reach it at all. Detachments show that the air has separated and turbulence builds up, causing drag and decreasing downforce, so the teams will be hoping that the car doesn’t come back with any of those signs.
Thanks for reading once again, I really appreciate it. If there is anything that you would like me to attempt to explain, please suggest it in the comments below any of my posts or contact me by email or social media outlets! Apologies for the poor coverage lately. My first exam is this week and they run until June 23, so I’ve been pretty busy. Hopefully I’ll be able to post the Canada Tech Highlights will up next week!