I've been studying the design of turbopumps and their impellers, all the design equations and what-not; this question concerns the contours of the impeller vanes. I'm going to attempt to enter aerospace engineering in the future, so I figured I might as well start getting exposure to the concepts now.
I'm currently attempting to design an impeller in CAD to test my knowledge of the equations as well as get better at CAD, but one of the facets of the design rather baffles me.
As you can see here (source, page 208):
The calculation of the radial contour of the impeller (that is, concerning $\beta_1$ and $\beta_2$ should be relatively easy given the other content in the paper, but radial impellers in turbochargers and other such equipment almost always appear to have a "lip" or forward facing top edge near the eye of the volute or casing inlet.
Here is an example of what I'm referring to:
You can tell that the vanes are backwards-curved, but near the top of the impeller vane closer to the eye, the curvature reverses and flares forward to approach near-flat slope.
My questions are:
What is the purpose of this axial contour (forgive me if that isn't the proper term)?
Are there specific design parameters associated with that contour? The Rocketdyne text above didn't seem to make any mention of the axial profiles of the impeller, other than the diagram to the left describing the dimensioning of the shrouds.
Where can I find an explanation and source of design information for how to design the contour?