Transient Flow and Pressure Fluctuation in a Variable-pitch Axial-flow Fan

A variable-pitch axial-flow fan of OB-84 type was taken as the object of study to simulate the pressure fluctuation at monitoring points and the characteristics of transient flow field based on the flow field in steady state considered as the initial flow field of unsteady state. Results show that all the pressure signals appear in the pattern of periodic or quasi-periodic fluctuation, and the pulsation intensity decreases with increasing flow rate, while the maximum value is located at the tip clearance. The maximum amplitudes at different monitoring points are presented at blade passing frequency, and the variation of flow rate only affects the time-frequency distribution. With the rise of flow rate, the average turbulent kinetic energy on the section at 10% blade height improves, and the high-pressure region at outlet section of impeller moves to the hub. The turbulent kinetic energy is enhanced with duration at trailing edge of blades and in the passage between adjacent blades. The high-pressure region at outlet section of impeller reciprocates between the casing and the hub during the rotation of impeller.