Active feedback control of stall in an axial flow fan under dynamic inflow distortion

This work proposes an active feedback control strategy using cross-correlation technique in a single stage axial flow fan operating under dynamic inflow distortion. Experiments were carried out under dynamic inflow distortion at the design speed with only three sensors and actuators, each. The stall inception mechanism studies under dynamic inflow distortion were carried out using 1-D continuous Morlet wavelet transform. It was observed that stall inception under co- (in the same direction of rotor rotation) and counter-rotating (in the opposite direction of rotor rotation) inflow distortion occurred through long and short length-scale disturbances, respectively. The knowledge of the nature of instabilities under dynamic inflow distortion was used to set the threshold of the correlation coefficient. It was observed that the active feedback control strategy resulted in a stall onset delay of 125 ({reversed tilde equals}3.125. s) and 65 ({reversed tilde equals}1.625. s) rotor revolutions under co- and counter-rotating inflow distortions, respectively. The highest delay under co-rotating inflow distortion was attributed to the substantially higher stall warning time as compared to counter-rotating inflow distortion.