INSIGHT: How does IndyCar deal with an airscreen pool problem

The NTT IndyCar Series is making progress in solving the problem of rain gathering at the front of its air fender.

It was highlighted as a problem in the final stages of the Indianapolis Grand Prix in May, and a number of drivers described a strange aerodynamic phenomenon where torrential rain while sprinting into the first turn produced a large bubble of water that was sitting directly in a line. Their view was rejected. They scattered until they moved away from Turn 1 and into areas with light rain. Returning to Turn 1 on the next lap could cause this phenomenon to happen over and over again.

With the airflow attaching the mass of water to the face of the windshield when approaching Turn 1, some drivers – in particular, those who run close to each other – said they were all bubbling blind and resorted to looking from the sides of the cockpit as a temporary solution.

According to Tino Belli, IndyCar’s director of aerodynamic development, the process of identifying the source of the problem and finding a solution to prevent the problem from recurring has been in the works for months with the support of Dallara, IndyCar’s official chassis partner.

“After the GP, we spoke with Dallara about whether the windshield wipers could work, which they said was impossible for a number of reasons,” Bailey told RACER. “One of them is the shape, but it’s not just the shape; we’re short on electricity and short on space. We also invited Honda and Chevy to solve this problem with us and Dallara ended up doing most of the work.

“So what they wanted to do was look at this water bubble on the windshield in a CFD (Computational Fluid Dynamics), and no one had done that before. Honda and Dallara both use ANSYS (software) for their CFD contract and have presented this possible way to check if We could see what was happening with the technique of placing a five-millimeter-thick hydro film over the air barrier and then blowing air almost over it.”

Before looking for repairs, Bailey and Dallara needed to understand how a 5mm layer of water would be affected by the airflow flowing over and around the air barrier. Using the Dallara DW12 hypothetical model in CFD, baseline tests were performed to determine water film surface velocities across the face of the visor.

These initial drills revealed slower air speeds were found in the middle of the air fender – exactly in the area where drivers complained about the water bubble – while higher speeds were found outside the bubble, helping to clean the water away from the surroundings. . In the blue areas, the film of water was projected onto the lower end of the motion by the air current, somewhere at or below five meters per second.

Lighter and darker shades of green were more promising, with water surface velocities recorded in the range of six to seven meters per second, and in yellow and red, velocities increased to eight to 10 meters per second. The basic runs created a clear path to correct the assembly problem: making aerodynamic changes somewhere on the chassis – before the air fender – and possibly on the aerodynamic fender itself that would raise the air velocity in the middle of the machine.

In simpler terms, Belli, Dallara and Honda are tasked with turning the blue and green slow zones into yellow and red.

“The blue was at 4.95 meters per second. And then, as you walk around the site as it gets greener, then yellow, you see the speed of the water film accelerate,” Bailey says. “That told us we could see something and we could quantify it. And we were also looking at ventilation.”

As the new season approaches, IndyCar teams will continue to use the same Airoscreen model introduced in 2020 before introducing a new, lighter version in 2024. A thinner, lighter PPG polycarbonate screen and a lighter titanium frame have been developed. – The Aura – Also powered by Pankl which uses a new manufacturing process which, when combined with the new screen, is expected to cut 10 pounds off the unit.

The development of the aeroscreen 2.0 also allowed Belli to experiment with both virtual and real-world tests aimed at improving cockpit cooling and ventilation which in turn gave some guidance on ways to improve air velocity in the problem area found in the water-film CFD experiments.

“The idea is that when we do the lightweight windshield, we wanted to collect data on places on the air fender where we could increase the cockpit ventilation,” Bailey says. “We tried a few things during the March 29th 2.4L (2024 engine test on the IMS road track) with Scott Dixon where we cut some holes in the screen in areas that didn’t diminish its safety in any way and Scott had given us feedback on what he felt worked. Better.

“The rectangle we cut was near the base of the air barrier where it happened to be 4.95 meters per second, and he said he could feel that much more than most of the other holes.”

In modeling the various holes, rectangles and slits cut in the fender for CFD tests, a favorite Dixon near the base of the fender also helped improve air velocity. Virtual vortex generators have been tried along with several iterations that are currently being evaluated.

In all, 22 significant solutions ran to solve the water bubble problem in CFD. These findings went to a 39-page report for all parties to review, and as expected, many of these 22 ideas were tried and found to be unsuccessful. The most influential concepts were moved forward for further testing that helped the series find answers that are likely to be implemented in 2023.

Regardless of which air vent might be performed in the future, Dallara and the CFD team designed a small pair of hypothetical curved vanes that sit atop the shock cover that did miracles to speed up the air and direct it where it’s needed when it hits. Air barrier at a speed close to 10 meters per second. Among all the concepts tried in CFD, shock cover rotors are the leading solution to the water pool problem.

“We also looked, in CFD only, at what the aerodynamic effects are of how much downforce you lose, and how much drag you gain,” Bailey says. “And remember, this is only for road cycles where we are in higher downforce configurations. The changes are very small. If we do what we are looking for, it will be the same for everyone.”

“From CFD numbers, you’d lose nine pounds of forward downforce, and you’d lose six pounds of rear downforce. And your overall equilibrium (center of pressure) changes by 0.1. So it’s negligible at 14 pounds of downforce with no change in drag and very little change In balance. That’s where we are now. And Dallara makes a pair of quills for us to see in person.”

More testing needs to be done before IndyCar is ready to commission Dallara to manufacture 60 pairs of blades for field-wide use in 2023, and if all goes according to plan, proof of concept will be forthcoming outside of the CFD.

“At the end of this process, you’ll see we’re trying to see if we can actually move this into a wind tunnel with water in it,” Bailey says. “This is a completely new phenomenon. So lots and lots of configurations we’ve had to get close to what could be the solution, and now we’re starting to narrow it down.

“The next step is trying to find a wind tunnel where we put a camera inside the cockpit and take a driver with us for testing and spray water at high speed on the car. It’s not as easy as it sounds, because no one has really done this with an IndyCar with a screen. So we’re currently working with Honda and its new Halo tunnel in Ohio about potentially testing this with water.”

A final call is expected by IndyCar in December on how the air bubble water solution will move forward. Input will be requested from team owners and team managers on whether the rotors and any other repairs should be made mandatory on each ride, or installed and removed later after trying the wet road and street courses.

“We have to give Dallara a huge credit for taking the lead on this and dedicating a significant amount of time and resources to getting us where we are now,” says Bailey. And Honda, which has been increasingly supporting the project. It’s been several months since the 22 configurations were created, and Dallara and Honda both deserve the lion’s share of the credit for pushing this matter toward a resolution.”