Velocity triangles axial

Supposing constant rotational speeds, no slip, and an axial inlet, the velocity triangles are as shown in Figure 6-10. For the radial vane, the absolute tangential fluid velocity at the impeller exit is constant—even if the flow rate is increased or decreased. 

Figure 7-17. Typical velocity triangles for an axial-flow compressor.

In this section, the rotational velocity is directly proportional to the rotational velocity n according to the equation u — irDn. The impeller blade angles remain the same regardless of the rotational velocity of the impeller. Hence, the inlet and exit velocity triangles have the same form. The axial velocity of an axial fan changes directly proportionally to the circumference velocity u. This is also valid for the radial velocity at the outer circumference of a radial impeller fan. These velocities are directly proportional to the fan flow volume hence. 

The regulation of axial fan blade angle also influences the inlet and exit velocity triangles in such a way that the axial velocity and thus the volume flow change. When the relative velocity remains parallel to the blade, the efficiency remains high (Fig. 9.52). 

FIGURE 9.S2 Influence of axial Ian blade angle on volume flow and velocity triangles. 

It is also evident that the absolute outlet velocity, cj, emerges axially at maximum efficiency, i.e. 02 = 90°, since triangles ABD and EBC are congruent on the basis of two sides and included angle ... 

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