Research On The Effect Mechanism Of Adjacent Abnormal Blade On Stall Inception In A Two-stage Variable Pitch Axial-flow Fan

By changing the installation angle of the rotor,the adjustable axial fans adjust the flow to keep the high efficiency in a large flow range during the operation.It is an efficient adjustment way to reduce the loss of throttle effectively.At present,there is a phenomenon occurs,which one or more moving blade installation angles will float or not synchronized with the other moving leaves during the running of the adjustable axial fans.The phenomenon will cause the change of the fan characteristic curve,even more,the blanketing phenomenon will generate when a slight disturbance appear in the axial fans.The operating performance and efficiency is affected seriously by the phenomenon.In this paper,the two-stage adjustable axial fans of a power plant is studied,the adjacent abnormal blade appear in the second rotor.The starting position and style of the stall inception,so as the 3D unsteady evolution process of the rotating stall are analyzed.The analysis results with equal abnormal angle show that: Abnormal blade angle has an effect on the performance of the fan,when the blade angle is-9°,the safety margin of fan reduces;when the blade angle is +9° the safety margin of fan increases.The adjacent abnormal blade has no effect on the initial position of the rotating stall,the rotating stall coming into being in the second rotor firstly.The stall induced mechanism of axial flow fan has been changed by the abnormal blade angle,when the blade angle is +9°,stall inception first appeared at the top of +9°blade suction surface,the area of the separation zone gradually increased,and finally developed into a recirculation zone,when the recirculation zone increases to a certain extent,it will fall off from the top of the abnormal blade to the back of the channel,and the +9° abnormal blade suction surface will continue to produce new flow separation zone and recirculation zone,the type of stall inception is mode wave.when the blade angle is-9°,a small range flow separation region is generated at the top of the blade,when flow separation area accumulated to a certain extent,it will form a recirculation zone which is stall inception,the type of stall inception is spike.when blade angle is +-9°(+9° blade in the counter-clockwise direction of-9° blade)and-+9°,the safety margin of fan increase,the rotating stall coming into being in the second rotor firstly.when blade angle is +-9°,the stall induced mechanism is the same as +9°,the type of stall inception is mode wave.when blade angle is-+9°,the stall induced mechanism is the same as-9°,the type of stall inception is spike.