AlphaTauri had a strong pre-season overall, with the AT02 showing a good turn of pace, although there were a few reliability issues. During the test itself, the team did not introduce a large number of aerodynamic parts like many other teams, although it did compare two diffuser designs. In this article, a few areas of interest across the car are discussed.
Starting at the front of the car, for 2021 AlphaTauri has introduced a new front wing, with a single element connection to the mainplane, down from three elements in 2020. This design closely resembles that which Red Bull introduced for the Turkish GP in 2020 and has retained, on the whole, for this season.
The main changes are inboard, with the mainplane featuring a curl just outboard of the Y250 region. This will locally offload the mainplane by reducing the impact of the ground plane, but in doing so the losses dragged into the Y250 are also lowered. This is a positive compromise, so long as the load lost can be recovered elsewhere on the wing without creating additional issues.
Further back, at the front of the floor, AlphaTauri has gone in a different direction to other teams with its front-of-floor edge curl. With the 2021 rules, the slots along the floor edge (including inboard of this curl) have been removed, which will make the flow health on the underside of the curl worse.
This curl is important in contributing to the downforce of the entire bargeboard and floor leading edge system, as it acts as an exit condition. Therefore, while it is desirable to load it up, it is also crucial for it to have consistently good flow health across the aerodynamic map.
As a result, many teams have backed off the curl for 2021 to keep it attached, but then added a double element flap above it (teams only had a single element flap in 2020) to further reduce separation and extract more load by increasing the upwash. On the contrary, AlphaTauri has actually increased the height of the curl to the maximum permitted by the regulations (50 mm), and still does not have a flap above. It would be surprising if the team has managed to keep it attached, though perhaps developments upstream have improved the underside onset flow. Alternatively it may have accepted some flow separation if the overall load still increased, though this is risky because if the flow health at track is worse than in CFD/wind tunnel, the entire front-of-floor aerodynamic system could suffer considerably. Time will tell as to whether the team remains an outlier in this regard.
At the rear of the floor, AlphaTauri has also introduced a curl, which a few other teams have, albeit to a much lesser extent. This curl does feature a flap above it, most likely to improve flow health as discussed above. It will produce some local load as there will be an outwash component to the flow velocity here. This suction will also help to move the vortex formed off the edge of the floor further outboard, closer to the tyre, moving the downwash it induces into a position that minimises the tyre squirt. This should improve the energy of the flow in the diffuser and hence rear downforce.
For 2021, the rear brake duct wing regulations have been changed, with the lower part of the legality box trimmed by 40 mm. This left teams with a choice – either run with the lower portion of these wings trimmed (as per the intention of the regulations), or sweep the winglets up as they move inboard, thereby remaining within the legality boxes and maintaining the previous winglet width. Judging by the evidence of testing, those who generally run higher rake (Red Bull, AlphaTauri, Williams) have opted for the latter approach, while those running with lower rake have favoured the former.
The vortices shed off these winglets are very important in bringing high energy flow from above the diffuser down through the gap between the diffuser Y450 edge and the rear tyre, to control tyre wake losses. In previous years, the teams running lower rake had the tips of these winglets lower down than those with higher rake, in order to maintain a similar interaction with the top surface of the diffuser. Given the legality change for this year, it is likely that those with low rake no longer benefit from the wide span winglets as the extra span is too high relative to the diffuser. On the contrary, those with higher rake are still in a position to extract performance from the extra span.
In the case of AlphaTauri, which was helpful enough to show its actual winglets in its launch renders, the transition between the two legality boxes is very sharp (see above) compared to, say Williams. In doing this there will be a loading discontinuity on the winglets at the transition, and some vorticity will be shed here that out-washes the tyre wake and improves the effective expansion of the diffuser. Although this region of the car is hidden away most of the time, its importance in creating rear downforce cannot be underestimated and it will be fascinating to see how teams develop this area for the rest of the season.
Lastly, the team had two diffuser designs available during testing. The first appeared to be a legalised version of the 2020-spec, while the second included an additional fence. This would suggest that the team now has five fences on each side (including the one that defines the outer wall of the diffuser), the highest seen for some time. The benefit of having more fences is that each fence is less loaded for a given overall diffuser load, allowing improved flow quality on the elements and vortices less prone to breakdown. However, the difficulty with more fences is that greater development is required to optimise their aerodynamic interaction. It is also possible that the team wanted to recover the lost outwash from the reduced height fences for 2021, but could not load up the existing fences sufficiently, therefore requiring the addition of a new one.
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