Ferrari, Project 676: CFD divided into two parts to optimize correlation with wind tunnel

Ferrari, Project 676, has the need to bring a world championship title back to Maranello, which has been missing for more than 16 years now. The ground to recover against Red Bull is quite extensive, but at the dawn of a new racing campaign, the Ferrari legacy imposes maximum objectives. Among the multitude of elements useful for winning, the field of simulation holds significant importance in today’s modern Formula One, where on-track tests seem like a distant dream.

The structure of the calendar and the restrictions imposed by the FIA in terms of private tests minimize the hours available to teams to try out new elements to introduce on the car. The three meager days of pre-season tests, some tests with new Pirelli tires, and the introductory free practices during race weekends are nothing compared to the thousands of kilometers teams used to cover on private circuits until 2009.

It is obvious and mandatory to resort to simulations, divided into three macro areas. The “simulation environments” in chronological order: Finite Element Method (FEM) structural analysis and Computational Fluid Dynamics (CFD), wind tunnel, and finally, the driver simulator for weekend preparation. Today, we will try to understand how these technologies are exploited by the Maranello-based team, with the goal of gaining time per lap compared to the reigning world champions and making the car more “predictable.” Additionally, we will analyze the major difficulties encountered in data correlation.

Before continuing the analysis, it is important to note that, in addition to the prohibitions on private on-track tests, the FIA has decided to limit the hours available, computing power, and executable tests in simulators. Under the current regulations, teams perform in two months the same amount of testing that was done in a week years ago. These stringent rules force manufacturers to choose which updates to implement and test, even before hitting the monetary limit imposed by the budget cap.

To achieve excellent results from simulations, it is essential to have a good method: understanding which of the multiple developments can provide the best performance upgrade, obviously before embarking on the design phase. To do this, in most cases, a comparison is made between one’s own car and that of competitors. If a car can take a corner 10 km/h faster than yours, in practice, it means that the regulations allow developing the car to be faster.

For this simple reason, it is necessary to study and achieve the best updates to match or surpass the opponent on that specific reference. Another development method involves internally setting a goal: the total load to be obtained or the power developed by the power unit. With a reference number, the working group will try to get as close as possible to that data.

Once these choices are made, the design phase can begin in collaboration between various departments. After designing various components, the first of the three simulation steps can be initiated through structural and aerodynamic studies. FEM analyses allow finding defects in the construction of the elements composing the “skeleton” of the car. In this case, the main focus is on the new chassis, which must be completed before the end of the current championship.

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Thanks to simulations, technicians can understand where material can be removed and where it needs to be added. Furthermore, it is possible to simulate an impact to verify if the crash structures and the chassis itself can withstand the “G” forces imposed by regulations. Secondly, the design and simulation of the aerodynamic architecture are carried out. In this case, software is used to simulate the behavior of some aerodynamic components or even the entire car when it is hit by air.

In the computing environment, the flow patterns are displayed, identifying areas at different pressures, the vortices that are created, the wake, and the CPT: Total pressure coefficient. A problem that Ferrari technicians faced when simulating the entire car was optimizations on the structure’s nodes to perform a simulation within the computing power limits imposed by the regulations.

These simplifications can lead to various data correlation and car optimization problems through wind tunnel and on-track tests. The CFD environment is also divided into two parts. In the first, a car that reflects the real measurements is simulated, and in the second, a smaller-sized model is used with the airspeed that hits the car typical of wind tunnels.

This latter environment is useful in comparing data between CFD and the wind tunnel, especially when the data do not match or when updates need to be tested first on the computer and then in the wind tunnel. One problem related to wind tunnel simulations is the constraints imposed by the FIA in terms of wind speed and Reynolds numbers (air pressure and temperature). The car can be hit by a flow with a maximum speed of 50 m/s, or 180 km/h.

These values are relatively low and do not allow checking the flow’s behavior on long straights, where the air flow pressure flexes the aerodynamic elements. To overcome this issue, Ferrari technicians, through FEM simulations, understand how aerodynamic appendages change their shape at high speeds and manufacture new deflected elements to mount on the car.

At this point, the new pieces are applied to the car and taken to the wind tunnel to check the behavior of the air hitting the slightly deformed elements (the flow always arrives at the car at 180 km/h). One difference between CFD simulation and wind tunnel simulation is the impossibility, in the latter, of rotating the tires and understanding how the flow behaves in a turn.

When a section is covered with wheels not perpendicular to the air, the flow sent to the bottom has lower energy compared to when on a straight. The causes are the tire turbulences, which lead to lower load generation. To overcome this problem, the cars of the past generation used bargeboards behind the front tires, making the flow more laminar in its path to the bottom.

Modern wing cars do not have these aerodynamic appendages. To understand how air is sent to the bottom with the wheels turned, only CFD simulation is used, comparing the data with those obtained on the track. In the wind tunnel, to perfectly simulate every aerodynamic modification possible on the car, technicians divide the aerodynamic components covering the chassis and engine into smaller parts. The engine cover, for example, which we see as a single piece mounted and disassembled by mechanics during race weekends, is divided into smaller pieces and assembled during the design and simulation phase.

This allows changing angles and shapes of each small part of the bodywork to optimize the aerodynamics of the complete component and determine more suitable lines. Another advantage given by the wind tunnel to technicians is the ability to rotate the car at a certain angle to simulate crosswinds. We know how sensitive the SF-23 was to directional changes in the wind, and this type of analysis has significantly helped Ferrari ensure greater robustness and a variety of future aerodynamic analyses.