Why Mercedes want to change KEY W14 concept

After a ‘bouncy’ 2022 F1 season, 2023 was expected to be the year the Mercedes AMG F1 team would make a car capable of challenging the dominant 2022 champions Max Verstappen and Red Bull.

However, this season has been a series of reflections on the decisions made to evolve their ‘Zero Pod' sidepod philosophy, which in the words of Toto Wolff had 'untapped potential' in 2022 because they could not run their car at low ride heights.

Let’s just say that Toto has run out of liking ‘untapped’ potential, and wants Brackley to deliver something that actually delivers victories. For this, he’s brought his old gunner James Allison back.

Meanwhile, Fernando Alonso made a good career jump for a change, moving to Aston Martin, who shifted their development philosophy to follow Red Bull last year. With Dan Fallows, former head of aerodynamics at Red Bull as their new technical director this year, they have come out with their own flavour of design. A design, in which Fernando can slide to podiums and potentially victories using the ‘waterslide’ sidepods.

So what is holding the W14 back? Or better, why is the wide sidepod philosophy better than the narrow one for the 2022 regulations? Let's dive into these using test cases from CFD (Computational Fluid Dynamics).

Disclaimer: The models used in the CFD test cases are not an accurate representation of the real cars. The intention here is to try and isolate the effect of the sidepods and potentially discover aero mechanisms at play. Readers be advised that the aerodynamics around an F1 car are an ecosystem and anything affects everything.

Aston Martin's Red Bull Inspired wide sidepods

Smooth undercut philosophy and its ability to divide the flow into two specific regions.

The image below shows the surface pressure distribution and surface airflow lines for W14 and AMR23-type models simulated in CFD. The wide sidepods clearly divide the incoming air into two regions, one going around the lower half of the sidepods (red arrows) and one going above the sidepods (black arrows).

The airflow following the red arrows continuously feeds the diffuser (which is an extremely powerful aero device, especially on the 2022 cars) and prevents losses from the rear tyre contact patch from seeping into the diffuser. These losses usually tend to be the diffuser's main performance limiter.

The airflow following the black arrows goes over the sidepods and into the waterslides coming out over the top surface of the diffuser ramp, feeding flow to the beam wing, which further helps in extracting more performance from the diffuser.

The W14 philosophy, however, has no such distinction in flow, where geometry is used to guide airflow to a specific region. It instead depends on vortex structures and pressure differentials off-body to guide airflow to specific regions, which is always less tolerant to changing attitudes of the car in terms of steer, yaw, roll and pitch.

Effect of 'undercut' sidepods vs W14 style 'mid-wing' sidepods

With the complex bargeboards banned for the 2022 season, it was important for teams to find an alternative method to deal with the turbulent and loss-y front wheel wake which – if not treated properly – makes its way into the floor and the rear end of the car, limiting the downforce generation capability of the car.

The wide sidepod with undercuts creates a region of high static pressure behind the front tyre. This results in a lot of outwash behind the tyre and floor edges, which pushes the tyre wake away from the bodywork and the floor, preventing the losses from being ingested by the floor and the diffuser.

The biggest advantage of this brute-force mechanism is that it's consistent across all the car attitudes as it goes around the track and – even bigger – works even better in yaw conditions, which is normally where teams start to struggle with front-wheel wake control.

The W14 sidepods, however, rely on the pressurisation and tip vortex from the mid wing. How strong this pressurisation is relative to the one from the undercut philosophy? In reality, we don't know, but our simulations show us that they are evenly matched. In addition to that, the tyre wake is outwashed via the tip vortex from the mid-wing.

But the moment you jump into yaw simulations, the undercut philosophy clears wins because the mid wing pressurisation and tip vortex strength are more sensitive to car attitude changes than the undercut aero philosophy. As such, the wide sidepod with undercut is a more robust aero mechanism than using a mid-wing for the same purposes across the range of conditions an F1 car goes through.

Different Aero Philosophy

F1 car aerodynamics is vortex dominated, which is to say that you have multiple sources of vortices, and they interact with each other to define the final flowfield. These aerodynamic structures are not just details, but define the way airflow navigates around the car, i.e. the aero philosophy of the car itself.

The difference in vortex distributions is probably the most visual aero mechanism that can be seen through our simulations. For the Aston Martin (left), you can see that there are two main counter-rotating structures whose effective flow vector lands up feeding high-velocity air from outside to the rear part of the car following the sidepod walls. This mechanism might be what has given Aston Martin such a stable rear end this year.

If you look at the Mercedes on the right, you see three vortices, two of which are the same as with Aston Martin (but weaker) and a stronger third vortex close to the chassis which comes from the tips of the mid-wing.

Together they potentially form an effective flow vector (as shown) in the upward direction, which fails to feed high-energy air to the rear of the car consistently. This also might tie up with Hamilton’s comments about a poor rear end from testing.

As Toto Wolff says, the stopwatch does not lie, and Mercedes are no exception. Looking at their body language early in the season, they seemed quite confident that they had hit internal targets. Aston Martin, however, showed the potential jump in performance that was there to be had, a whopping 1.5 seconds faster.

This is what has convinced Mercedes and Toto that continuing the zero pod concept would not help. They don't need 2-3 tenths to be up there to fight for victories, they need at least 0.6-1 sec in race pace even if Red Bull don't develop their car at all, which is a lot of performance in F1.

Will Mercedes be able to develop and be competitive with their W14B? Imola will tell!