22 – FAN TESTING

Publisher Summary This chapter discusses fan testing. Fan testing is a very important aspect of the subject of ducted axial flow fans. In addition, while analytical methods are useful in estimating performance over the main operating range of the fan, rotor characteristics near the stall must be determined experimentally. Good inlet conditions are essential and hence, a streamlined entry to the duct must always be provided. In the test rig, wire screens at inlet have been used to vary the pressure rise across the rotor. A more usual arrangement consists of a variable area outlet by which the exit velocity and, hence, the discharge loss can be varied in a continuous manner. To ensure a good inlet flow distribution, the area in the vicinity of the bellmouth should be kept free of obstructions. The recirculation pattern of the air can also cause experimental difficulties and hence, it is advisable either to have the test rig in a large room or to provide a baffle system through which the air has to pass when returning to the inlet end of the room.