A torsional vibration coupling dynamic modeling and analysis method for engine/power transmission systems in coaxial high-speed helicopters

Abstract To address the torsional vibration coupling problem in coaxial high-speed helicopters – involving dual rotors, a thrust propeller, power transmission mechanisms, and the engine under multi-source time-domain strong excitations with high and low rotor speeds – this paper proposes a dynamic modeling and analysis method based on the RK4 (Runge-Kutta fourth-order) method for the engine/power transmission system. The torsional vibration signals calculated by the model are further processed via Fourier transform to analyze the system’s natural frequency characteristics. Numerical simulation results demonstrate that the maximum relative error between the first four natural frequencies calculated by the model and reference values is 3.51 %, validating the model’s high reliability. Under high rotor speed conditions, the contributions of the 1st & 2nd, 3rd, and 4th natural frequency components in the power turbine speed signal reach 35.94 %, 14.09 %, and 11.38 %, respectively. In low rotor speed mode, these proportions are 39.84 %, 10.12 %, and 8.72 %, respectively.