where Ws is the impeller shaft power.
With this, we are now in a position to assess the performance of region A. For the test case fan geometry and fixed flow regions shown in Fig. 10, we calculate the ideal pressure rise and loss breakdown as shown in Fig. 13 and Fig. 14. From this it is clear that the second stage produces most of the useful work at high flow rates, whereas the first stage is increasingly important at reduced flows. It should be emphasized that the ratio of work is a strong function of S1/S4, and that this case assumes fixed flow regions. The affects of flow region variation on performance will be discussed in more detail later. The loss breakdown in Fig. 14 shows the relative contributions of blade, diffuser and discharge losses using a constant value of 0.8 for diffuser efficiency (in this case AR is less than unity). Considering Fig. 14 along with the velocity diagram, it is important to note the high second stage exit velocity. The associated discharge kinetic energy can be used effectively for thrust or boundary-layer blowing in aircraft applications. However, it produces a need for energy recovery in static applications, as is apparent in the large exit loss. We will return to this test case in Section 2.4 and discuss the calculated performance in relation to test data, but first we will consider flow regions B and C.