That's natural : P but the side flow is more interesting IMO.
If you compare it with the RS.20, it seems there's still a decent amount of downwash there. The lower natural flowviz stream seems to be going similar path, or even at a steeper angle, so it seems to join the floor earlier than on the RS... and more inboard obviously.
I could be wrong, but on the RS.20, that flow was probably attracted by a low pressure area that was purposefully created near the floor by the RB-style sweptback side hump, and helped by the 'ramp', whereas the A521 uses the carved sides of its sidepods instead to force that side air downwards, so in a more 'classic' manner, and maybe for the same result...
And maybe that lower stream is stronger on the A521.
So that lower A521 stream is certainly similar to the RS.18 and 19 due to the similar sidepod shape, at their first half atleat... but the difference between 2019 and 2021 concerns the other stream, the upper one IMO. On the A521 it joins the lower one and the coke bottle area easier than the RS.19 thanks to the Alpine's more overcut bodywork compared to 2019.
But real aerodynamicists here and mud flowviz experts know better than armchair aerodynamicists
-
So it seems thy didnt race the modified rear brake winglets that aerofoilf1 mentioned
