They've derived exact mathematical expressions for the shapes and locations of those flow separations, and it sounded like the whole derivation was based on the assumption of incompressibility, so I'm not sure how extensible their approach is to compressible flow.
That said, it's totally true that you could use this sort of code in gasdynamics situations where the compressibility doesn't matter much, as you pointed out.
The experimental setup they validated their code with used three liquids -- Fluorinert, glycerol, and vegetable oil -- shearing past each other and the walls of a container while being stirred slowly. All incompressible, true, but perhaps chosen for experimental convenience rather than any problem with their theory's handling of compressibility.
That said, it's totally true that you could use this sort of code in gasdynamics situations where the compressibility doesn't matter much, as you pointed out.
The experimental setup they validated their code with used three liquids -- Fluorinert, glycerol, and vegetable oil -- shearing past each other and the walls of a container while being stirred slowly. All incompressible, true, but perhaps chosen for experimental convenience rather than any problem with their theory's handling of compressibility.