If you are studying the fluid flow around the blade, you won’t need the blade itself. That is unless you have heat transfer or FSI or something else that you are requires you to model the blade. That means that you can suppress (or even delete) the blade (named ClosedSurface.3) in your model.

The inflation will be on the fluid body (named Domain in your model). But it will only be on the faces that interact with the blade. When you are selecting the faces for the inflation’s definition, then you select all these surfaces–not the planar faces of the Domain body. (Side note here, you may want them on the shroud/hub surfaces too.)