Looking at your question, I think this part is actually on topic:
Do OpenSource compressor or turbine blade designs exist (e.g. NACA
airfoil profiles for wings) ?
It's this part that is entirely out of bounds:
Could you provide detailed dimensions --in particular for the
cross-section profiles and stacking laws--- as well as the associated
material properties ?
The problem isn't how specific an answer you'd get; on the contrary, specific answers are great! The problem is that you wouldn't just get one specific answer. You might get twenty, each of them different, many of them equally "correct" so that readers would not be presented with an objective ranking of solutions. Instead they'd see a subjective ranking of solutions, based on what the readers like or prefer or are most familiar with.
Going back to the first part of the question, though, I think the topic is very interesting and relevant to engineering. It's weak mainly because without the second part (which is a non-starter) it's a yes-or-no question; either these schematics exist, or they don't.
In my view, you can make this a great question by dropping the request part and expanding on the Open Source part a little, to invite why and how answers instead of just yes or no. Do you have a reason to believe these designs do or do not exist? If so, how does your professional experience and any research you've done on the topic support that belief?
I think a better version of this question would ask about the challenges of providing Open Source engineering designs (specifically compressor or turbine blade designs, in this case—I did not mean to imply expanding the scope to all designs as that would be quite broad!). What are they? How can they be overcome? Good answers to such a question would tend to lead you to the resources you need, but would also be rankable, useful artifacts for the site going forward.
With respect to your other examples:
Asking for feedback on a specific design or schematic. The user provides the details and related issues in order to benefit from the
experience of the community and improve his/her design. See this
post from Electrical Engineering.
Interesting example. First thing I want to point out to you is that this question is going to be of very limited use to anyone other than the author. No-one with a specific problem is likely to find this question on a search engine; and if they do, it's very unlikely to contain answers relevant to their problem. Note that demand for this sort of individual review for source code was high enough that SO spun off Code Review, which I think (?) has been doing fairly well in beta, but offers a very different experience.
In my opinion, the question of whether we allow questions asking for general review of individual designs/schematics is separable from the rest of the discussion and deserves to be discussed and evaluated separately. That said, my position is that it should absolutely not be allowed on this site. Maybe on a spin-off site, after a successful launch for Engineering.SE, if there is sufficient demand.
Asking for explanations related to a drawing. Sometimes available schematics, either from books or articles, are somewhat unclear or
there is missing information (specially for beginner users) and asking
for clarification based on researchers experience can be extremely
helpful. See this post again from EE.
That's absolutely fine. The main problem I would identify with the example post is that the title's not at all searchable. The question being asked is very specific and there exists one objectively correct answer to how to read any given schematic (even if you have to ask the person who drew it to be certain). Experienced users should be vigilant in editing such questions to make sure they have explicit, searchable titles and good tags.