Boosting overtake with Drag Reduction System

“In the previous two posts around multiple car aerodynamics, we have discussed the wake generated by the lead car and how this affects the pressure and drag on the following car. We also introduced the idea of slipstreaming and how a reduction in energy and surface pressure can help the following car. In this article, we help quantify the differences and introduce DRS or ‘Drag Reduction System’, a tool introduced into Formula One back in 2011.

Let’s first consider a following car scenario with a 10m offset between the two vehicles in a straight-line. The wake generated by the lead car, reduces energy within the flow. This reduces both the drag and downforce of the following car. This can be seen in the movie above, where the flow behind the lead vehicle is orange and has had energy in the flow removed.

“The following car sees a 20% drag reduction compared to the lead vehicle.”

For the car in this example a 20% reduction in drag was observed at 50m/s (~112mph). A 30% reduction in downforce was also seen. This drag reduction means the vehicle has less resistance and can thus accelerate faster and reach a higher top speed, whilst in the wake of the lead vehicle. In a straight line the downforce reduction is not necessarily an issue, providing the overtake is completed before the corner entry. If it isn’t, this poses an issue as cornering performance is reduced whilst in this following car scenario.

DRS and its effect

DRS was introduced to help overtaking within Formula 1. The system allows for the opening of the rear wing flap, which creates an instant reduction in drag. In doing so we reduce downforce from the wing, which also influences the entire floor. For this vehicle, a 30% reduction in drag and 42% reduction in downforce was observed. The plots below show a comparison of CpX, the component of pressure acting in the direction of the vehicle, effectively showing drag. We can see that opening the DRS of the following car has reduced drag from the wing, but also the diffuser and wheels.

When compared to the following car without DRS a further 10% reduction in drag was seen. For this relatively underdeveloped car, the effect of following another vehicle was therefore relatively more significant than the effect of DRS. Formula 1 teams work to optimise the effect of DRS to maximise the reduction in drag, when DRS is applied. The aim is to reduce drag by more than just the drag from the flap itself.

We effectively work to try and make a chain reaction from DRS. If the flap opening can stall the main element, which can also help partially stall the floor or beam wing the effect is magnified. This can take some tuning as we need the aerodynamics of the car to be close to the edge of stall, to allow the impact of the DRS to trigger the chain. This pushes both computational modelling and scale wind tunnels to the limit and occasionally mistakes are made when things do not separate quite as desired. In future posts we will discuss the impact of following car distances and lateral offsets.