As the title suggests, I tried concatenating the inputs of both, like a game engine, hoping to achieve an overlay effect of heightnormal and noise (this is just an example; in reality, I might use various channels and blends for overlay and mixing), but nothing happened.

Is some kind of scaling required, or is the noise from the blend node simply not working?

Hi,

It should work. Most likely the noise values are very small compared to your existing normals, so the change is barely visible. Try temporarily cranking the noise amplitude way up to see if it's actually affecting the data.

Also, simply adding normals isn't a very meaningful operation, since you're no longer working with unit-length vectors. If you want a more visible overlay effect, you’ll usually get better results by either:

1. Blending the underlying height/displacement and then recomputing normals, or

2. Using a normalized / slerp-style blend between the two normal fields.