Prediction for critical speed of double spools system in aero engines

According to the rotor dynamical design requirements in aero engines, the critical speed prediction method for double spools system were put forward based on the finite element method and the vibration mode selection technique, and it was practical for solving engineering problems. The detailed solving process of the full method and the reduction method were discussed with a double spools example. It exhibited that the results obtained by both methods were exactly the same. However, the reduction method need less iterations and was more convenient to obtain the critical speed. The co-rotating double spools possessed five critical rotation speed, and the counter-rotating double spools had three more critical rotation speed in the same rotation speed range, whose modes were n=3, n=4 and n=5, respectively, caused by the anti-precession. The densification of the critical rotation speed would lead to the complexity in the rotor dynamical design in aero engines.