VIBRATION COUPLING EVALUATION AND OPTIMIZATION OF THREE SPOOL SYSTEM FOR VARIABLE CYCLE ENGINE

Variable cycle engines provide better fuel economy, additional thrust, and more durability than the state of art, because of solving the inherent contradiction between subsonic and supersonic flight through different thermal cycles, which is a promising solution for the future aero-engine. Due to the limitation of spatial dimensions by the new multi-bypass intake variable cycle configuration with inter-stage combustor, the matching three spool system adopts the support scheme with innershaft bearing and shared-support frame, which may lead to potential vibration coupling between three rotors.To solve this problem, the simulation of vibration coupling in three spool system has been conducted in this paper, and a quantitative evaluation method has been proposed. Then, the influence of parameters such as rotor shaft stiffness, support stiffness, and shared-support frame equivalent stiffness on vibration coupling are studied, and the key parameters are screened. Based on the sensitivity analysis, an optimization design example is carried out by applying genetic algorithm. The optimization results show that the three spool system reduces the vibration coupling between rotors by over 50%, which meets the requirements of rotordynamic design and has a promising engineering application prospect.