Leading edge or trailing edge stall? As I wrote last week, I'm doing a Benedek 10355 airfoil performance report.
At this point of the work I am analyzing the stall of the profile at a fixed Reynolds number.
The Benedek 10355 airfoil has a thickness of 10.1%.
Figure 1 shows the polar calculated with Xfoil at Reynolds number = 500,000.

Analyzing this curve, and comparing it with this answer, it seems to me that we are in the presence of a trailing edge stall.
In fact, after the stall angle ($\alpha_{stall} = 11.0°$), the decrease in the lift coefficient is gradual ... Then, however, at about $\alpha = 21°$ there is a sudden change in lift, as if a laminar bubble had &quot;burst&quot;.
Figure 2 shows the separated zone for $\alpha = \alpha_{stall} = 11.0°$.

Looking at the pressure coefficient, there appears to be a laminar bubble very close to the leading edge (Figure 3).
As the incidence increases, this bubble moves more and more towards the leading edge and, when $\alpha = 22°$, it &quot;disappears&quot;.
This makes me think that maybe at low incidences there is a trailing edge stall and then, going further, a leading edge stall ...
Maybe I'm missing something?
Thanks.
The Benedek 10355 clearly stalls with separation starting from the trailing edge.
There is some discussion whether a laminar-to-turbulent transition due to rising pressure will always involve a laminar separation bubble, however short. But that bubble does not constitute a leading edge stall.
XFOIL is not meant for flow simulation deep into the stall region. It does amazingly well to capture the initial stall but cannot possibly model the extended separated flow well into the stall accurately. I am actually surprised that it still produces converging results at such high angles of attack.
In short, I would not expect the XFOIL results above 12° AoA to model accurately what is happening in reality. Especially that sharp drop in lift at around 21° looks very much like the code settling on another solution but not something that can be expected in real life.