In the last article we discussed how the changes in downforce across the ride height range affect the overall car performance across the lap. In this article we will discuss how the flow in cornering conditions affect its performance.
The grip-limited sectors within lap are dominated by corners, therefore the aerodynamic package should be designed to withstand variations in steer/roll angles, flow curvature and crosswind, ultimately delivering downforce when it matters.
During cornering the car will be subjected to attitude changes throughout the different stages and speeds. In addition to the ride height changes discussed in the previous article, the engineers need also to consider the effect of the tyre attitude changes due to steer, as well as the effect of roll. Steer and roll are variables which tend to be very tightly coupled, not being easy to separate the effects of one or the other on track.
When subject to crosswind, the vector of the flow reaching the car will have an angle relative to its longitudinal axis. The effect of the side wind on the resultant flow vector will be proportionally larger in lower car speeds, in Formula 1 it is not unusual to measure wind angles above 10 degrees in low-speed corners.
And finally, during cornering the car performs a curved trajectory, hence the car is subjected to a curved flow field. If crosswind effects were to be ignored, the flow curvature would mean a plan view incidence angle at the front which then curves towards a more neutral or opposite sign angle at the rear.
Within the aerodynamic development process, engineers use historical and simulation data to estimate the amount of time the car will spend at given operating conditions. With this data in hand, they then decide the conditions which will be given the highest priority in the map, often through a weighted averaging approach.
As a result, a team which chooses to develop their car focusing on high-speed corners will likely end up with a package which generates substantial downforce in low yaw/low steer conditions but potentially results in sharp losses as soon as moderate to high yaw/steer angles are reached. Another team might focus on low-speed corners, in which case a more robust aerodynamic package would likely be designed with a more linear aerodynamic response across the map.
While the second car would be considered less sensitive to crosswind and more driveable across the lap, it would potentially be too slow in the medium and high-speed sectors compared to the first. Like discussed in the previous article, the teams have to strike a balance between various performance trade-offs, the car performance needs to be judged not only by the absolute levels of downforce and drag at a few operating conditions, but also by the variability of its performance across the entire operating range.
In the next article we will discuss the effect of aerodynamics performance on the driver’s confidence levels and how this affects lap time.