While designining the geometry of different sections of the turbine blade, I've noticed that some of the sections (closer to and including the root) do not have visible gaps if viewed from the leading edge perpendicularly to direction of rotation, and that some (closer to and including the tip) have the gap. I'm interested if the presence of such gaps can affect the gas flow and therefore the possible efficiency of the turbine. I will provide the images of root and tip sections and velocity triangles for each of them.
In my opinion, the possibility to see through the blades is not important. The gas flow of course has a component in the blade movement direction. Aerodynamic design of the flow along the blade surface determines how high the suction side is and how high the leading edge needs to be.
My boss at an industrial gas turbine manufacturer stated as a rule of thumb that there would not be a sight line through the blades.