Is it acceptable to hide your affiliation in research paper?
You're trying to solve the wrong problem: either your work is a decent contribution and then it's worth publishing with your affiliation, or it's not and then it shouldn't be published at all (and anyway it's likely to get rejected in respectable venues).
So the real problem here is whether this work is a decent contribution. However you might not be able to make the call yourself:

You are a PhD student so you might not have enough experience to judge, and especially to judge your own work.
You also seem to assume that researchers in your university never produce any mediocre work, although this is very unlikely even for a top university.
The fact that you talk so negatively about your work might be a sign of impostor syndrom, a bias which frequently affects researchers (and not only them). The competitive environment of a top institution is a fertile ground for this kind of psychological bias.

But the solution is very simple: you just ask your PhD advisor their advice. It's precisely their job to teach you what is a decent contribution and what is not. If they tell you not to submit the work, then it's not even worth submitting. If they tell you to submit, then it was actually better than you thought and it means that you should revise your criteria.
You can even ask them about your idea to submit without the affiliation if you want. But be aware that they might laugh at the idea, it's not something academics do anywhere.