Taking the coupling between fan and low-pressure rotors of geared turbo fan (GTF) engine into consideration

a simplified model of rotor system and a critical speed calculation method for the model were proposed. Differences of critical speed results between the overall rotor system and the single rotor system were clarified. Influence of typical parameters on critical speed and dynamics of the rotor system was discussed. From the results

calculating the fan and low-pressure rotors separately causes deviation of natural frequency and loss of critical speed. Increase of the gearbox support stiffness leads to rise of critical speeds

while keeping the stiffness value below 106N/m may provide better dynamic characteristics. The flexural rigidity of the torque transmission shaft and radial stiffness of the gearbox have less impact on system's dynamic characteristics.