2.3. Flow in regions B and C
The impeller blading in region B acts essentially like a paddle wheel, and therefore the energy transfer is relatively low and inefficient. This region includes a through-flow, however, its contribution is normally quite small, and from a mean-line analysis standpoint its most important features are its size and influence on region A. Referring to the URANS velocity field data in Fig. 15, it can be seen that region B is defined by the “relative eddy” in the blade passage by the rear wall. Immediately adjacent to the eddy the flow moves through the blade passages in the rotating frame and can therefore be classified as part of region A. Through-flow streamlines in region B also graze region A, with those closer to the impeller interior seeing more cascade action and those toward the rear wall seeing less. With these observations it is logical to assume that region A extends fully to the boundary of the relative eddy, making the mass flow associated with region B quite small. Finally, since the flow speed in B must be very nearly the same as the blade speed, the work on the fluid is relatively low. As a result we neglect all aspects of region B except for its size and influence in bounding region A.