144
3 Fans
Similarly, by opening the rotor, characteristics can be shifted towards higher
flow rate and higher pressure rise, but limited due to separation at too large angles
of attack. Some larger industrial axial fans have rotor blades that are individually
adjustable at standstill.
3.7.4 Mixed-Flow Fans
Some forms closely approach the axial form and others closely approach the radial
form. Figure 3.33 shows the meridional section of a fan close to an axial type,
with small radius change of the average flow. The corresponding velocity triangles
show the axial velocity increase through the rotor by the decreasing blade height.
Fig. 3.32 Reduction of flow rate and pressure rise by turning rotor blades into a more tangential
position; top: vane ring downstream of rotor; bottom: vane ring upstream of rotor
Fig. 3.31 Flow patterns through an axial fan and consequences for the shape of the characteristic
curve. (Adapted from [9])
3 Fans
Similarly, by opening the rotor, characteristics can be shifted towards higher
flow rate and higher pressure rise, but limited due to separation at too large angles
of attack. Some larger industrial axial fans have rotor blades that are individually
adjustable at standstill.
3.7.4 Mixed-Flow Fans
Some forms closely approach the axial form and others closely approach the radial
form. Figure 3.33 shows the meridional section of a fan close to an axial type,
with small radius change of the average flow. The corresponding velocity triangles
show the axial velocity increase through the rotor by the decreasing blade height.
Fig. 3.32 Reduction of flow rate and pressure rise by turning rotor blades into a more tangential
position; top: vane ring downstream of rotor; bottom: vane ring upstream of rotor
Fig. 3.31 Flow patterns through an axial fan and consequences for the shape of the characteristic
curve. (Adapted from [9])