Alfa Romeo has already conducted a shakedown of its new C41 car ahead of pre-season testing this weekend, with the car present there quite different to the images shown at the team’s official launch, which had some 2020-spec parts fitted. The team had a disappointing 2020 season, although they did show strong performances on race day despite the lack of power from their Ferrari engine holding them back. This deficit should be significantly reduced this year which, together with some significant aerodynamic changes, could move the team closer to the front of the grid, at least in time if not position.
Starting with the front wing, the overall loading distribution is very similar to previous years, with Alfa Romeo loading the inboard of the wing much more so than the outboard. The most significant change concerns how the mainplane blends into the FIA-mandated neutral section, with a pronounced curl now present in this region. Raising the mainplane local to the Y250 position will help reduce losses here, particularly at low front ride height when the wing becomes more loaded. While offloading the wing locally, this will result in a cleaner Y250 vortex that is less prone to breakdown further downstream when it experiences an adverse pressure gradient, most notably from the pressure rise of the bargeboard. However, this load has to be recovered elsewhere on the wing to retain the same balance range, which might explain the lower mainplane height a little further outboard, increasing the ground effect and recovering some load. This will also ensure that the Y250 retains its strength, with vortex filaments at this span-wise location still feeding this vortex, as opposed to those further outboard on the front wing.
Elsewhere on the front wing, there has been some profile work, with the upper element in particular having a shorter chord. Also at the front of the car, the nose has been narrowed, following the trend of many other teams towards the front of the grid. Alfa Romeo have tended to change nose design quite significantly between seasons over the past few years, and this year is no exception. One of the main benefits of the narrower nose is that it keeps the Y250 vortex higher, by reducing the imaging effect with the outboard surface of the nose. This has a benefit downstream, particularly in conditions where the Y250 sits lowest relative to the floor leading edge, because it can prevent this vortex from passing under the floor.
In order to work as intended, many of the details on the ‘flat’ part of the bargeboard region are reliant on onset flow imposed by the Y250 when it sits above the floor, so if it drops below it a significant loss in downforce will follow. One downside of the narrow nose is that, under yaw, it provides less lateral blockage to the Y250, which on one side of the car is shifted towards the nose. At high yaw, this vortex can sit too far inboard on one side of the car, providing sub-optimal flow to the bargeboard region. This can be mitigated, however, by altering the design of the cape, which sheds a vortex that moves the Y250 vortex outboard.
On the C41, the cape features a drooped leading edge, which will result in the cape being loaded up under yaw on the same side as the more inboard Y250. This will strengthen the vortex it sheds, moving the Y250 further outboard, potentially recovering it to the position it had with the wider nose. The downside to a more loaded cape vortex is that is also moves the Y250 down, contrary to the motivation of the narrow nose in the first place. Therefore, it is clear that there is no silver bullet in this region, but there must be a trade-off of the various aerodynamic levers. A little further back, the front brake ducts have been altered in shape, with the lower part of the inlet narrowed significantly. This should improve the attachment of flow to the external surface of the front brake duct as there is reduced expansion. Given the team has used its two permissible development tokens on a new front impact structure for its narrower nose, the brakes will be the same as last year’s, but perhaps this altered inlet shape was designed to work with internal changes in the wheel to optimise through flow and improve tyre wake control\.
The bargeboard region is largely the same as last year, with some small evolutions. Firstly, it appears as if the main bargeboard has been moved slightly rearward at both its leading and trailing edges. With this change, the wheel wake gets pushed outboard a little further downstream. This is a negative for front downforce, but provides a benefit further rearward, as the clocking of the upper tyre wake is reduced. This improves the onset flow on to the rear wing, and also into the rear corner, improving diffuser performance.
The number of horizontal elements making up the sidepod vanes has been increased by one to four. These elements pressurise the region inboard of them, helping to keep the tyre wake outboard, while also producing some local load, as the flow incident upon them has a signifiant lateral velocity component. Further detail changes have been made to the upper bargeboard leading edge and the floor edge, while the trailing edge of the bargeboard has been stepped down in height. The latter is possibly due to this being an efficient downforce-to-drag trade-off, with the rear of the bargeboard quite rearward-facing.
The upwashing curl along the edge of the floor starts later than last year, but also extends further downstream. For 2021, the longitudinal slots along the edge of the floor have been banned, which means the health of the flow on the underside of this curl is worsened. This would explain why its height is reduced, and there are now two flap elements above it to help keep the flow attached and recover some load in this region. Finally, two vertical elements have been added that will promote some more outwash, and the vortices they shed may help delay the formation of the main floor edge vortex, keeping it further outboard and reducing the losses it produces in the outer part of the diffuser.
At the back of the car, the diffuser has also undergone some fairly significant changes, with the trailing edge height reduced noticeably along the outboard half. There are a few possible reasons why Alfa Romeo have made this change. Firstly, the flow may have been separating at the rear of the underside of the diffuser, so backing this area off would alleviate the issue. Secondly, the diffuser sidewall may have been struggling due to the reduced inboard fence height for 2021, and backing off the upwash, as opposed to the outwash, may have been the better option to improve this. Another alternative is that the team was looking to alter the interaction with the rear brake duct winglets (this diffuser change would increase their load), which have also been impacted by the regulation changes for 2021.
Dropping the main diffuser trailing edge increases the overall height/chord of the flap elements above it. This makes it more difficult to keep these elements attached, while also maintaining good suction to increase the diffuser vertical expansion. Therefore, the team has increased the number of elements to three in the region of reduced tailing edge height. Finally, note that the winglets at the centre of the diffuser have been modified subtly, most likely the result of some profile work.
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