We will start our new series on Aerodynamic Performance Modelling discussing performance metrics. The most basic questions in any aerodynamic development project are around the meaning of success.
The performance metrics could be discrete and objective, for example achieving a given target for lift/downforce, or an efficiency target, or a thrust target for a propeller. Or they could have multiple interconnected variables, often making the definition of success more subjective.
When we look at component level, defining performance metrics tend to be a relatively straightforward task, they are often well defined and objective. However, when the application moves into sub-systems and complete system levels, many more variables and outputs are at play, many of them being tightly coupled.
In the motorsport environment, the goal of the aerodynamicists is not to just add downforce and reduce drag. Their goal is to make the real car go faster on the track, considering multiple tracks in the racing season, multiple environmental conditions and operating conditions for the car.
While the “more downforce and less drag” approach remains a valid performance improvement if applicable uniformly to the entire aero map, more often aerodynamicists are faced with trade-offs of characteristics at different operating conditions. These translate into subtle but significant changes in the shape of the aero map, which will determine the aero loading at different ride heights, different stages of the corner, sensitivity to crosswind, ability to warm-up and look after the tyres, and how it might affect a given driver considering his/her style and preference.
For the racing team, therefore, it is crucial to develop performance metrics which accurately relate the aero map to on-track performance, which in turn will inform the aero development group what they need to achieve to make that car go faster on track. A poor correlation between the metrics and the on-track performance will lead to the progressive improvements seen in the wind tunnel and CFD not translating to race car performance.
In the next article, we will continue to discuss the same theme but applied to motorsports from the perspective of the governing bodies. We will also discuss aerodynamic performance metrics in the context of aerospace propellers.