archangel against Flak

The title basically gives it away: does freakshow with soulfright or archangel weapons can destroy stationary guns of the aegis for example?

Don't think so as they don't have a Ld score so they're immune

The Aegis is Battlefield Terrain, so is technically indestructable. Nothing can destroy it.

The Gun Emplacement is an interesting one though.
The rules for characteristic tests say "If the model has a characteristic of '-' or 0, it automatically fails the test.
Ok, granted, that refers to the characteristic test rather than being wounded, buts its an interesting angle.
An argument could be made for auto-wounding, although iuts not covered explicitly in the rules.

Squidmaster wrote:

The Gun Emplacement is an interesting one though.
The rules for characteristic tests say "If the model has a characteristic of '-' or 0, it automatically fails the test.

It also says "A model will sometimes be called upon to take a characteristic test. Such a test can be applied against any characteristic that the model has, except for Leadership and Armour Save" so I don't think we can really apply that here.

But if it's possible to take a test against every characteristics that the model has except leadership and Armour Save, does that mean that it can be forced to take a test on it despite not having that characteristics?

The rules specify when a test can be applied. By default, any situation not described would prevent a test even being taken.