Can anyone recommend lecture notes or (not too obscure) books that teaches me about gradient flow and what it has to do with PDEs? I did search but usually the material talks about dynamical systems which I don't want too much of. Something understandable by someone that knows about basic parabolic existence results would be good, and something that doesn't require knowledge of Riemannian geometry.
Thanks.
I would suggest
You could also consult
as well as this talk by Katy Craig (from 31:28 onwards), this lecture by Brittany Hamfeldt.
Other standard (but more advanced) references are Optimal Transport - Old and New by Cedric Villani and Gradient flows: in metric spaces and in the space of probability measures by Luigi Ambrosio, Nicola Gigli, and Giuseppe Savarè.