As explained in the description of the xflr5 background theory, XFoil is a powerful integral type 2d boundary layer solver that is still considered state-of-the-art some thirty years after its release.
With the increase of computing power, however, differential solvers are now being considered and may become the new standard for 2d boundary layer analyses. As a first step, one such method, described by Professors Cebeci and Cousteix in “Modeling and Computation of Boundary-Layer Flows”, has been implemented as an experimental feature in flow5. At this stage, it gives an interesting insight into the behaviour of 2d flows including information across the BL thickness, which is something that 2d integral methods such as the one implemented in XFoil do not provide.
However, from a practical point of view, the convergence is still too random for the method to be suitable for foil design and analysis. More development is required, including perhaps the implementation of transport-equation turbulence models instead of the Cebeci-Smith algebraic turbulence model currently employed.
Open-sourcing this part of the code or continuing the development with other parties interested in the subject are options. It is also something that I intend to continue investigating as a subject of personal research.
