航空发动机在起飞前需要在地面保持较高转速进行暖机，否则将造成起飞过程中的推力下降。针对上述问题，本文以小涵道比涡扇发动机核心机为对象，结合发动机流体域一维模型和固体域二维轴对称有限元模型，开发了一种流热固耦合计算方法，实现了发动机主流道、空气系统和多部件热分析及变形分析的跨尺度耦合仿真。仿真结果表明：叶尖间隙大于设计值是造成起飞阶段发动机推力下降的主要原因。暖机能够减小起飞过程中的叶尖间隙，高压涡轮效率提升0.85%，压气机效率提升0.5%，进而促使高压转速最大提升0.51%，增大了核心机流量，降低了发动机的涵道比，最终导致发动机起飞阶段的最小推力上升2.4%。研究结果进一步表明，增加暖机时间或增加暖机转速均可提升起飞推力，但暖机转速小于0.75时无法通过增加转速减小高压涡轮叶尖间隙。最后基于序列二次规划算法，构建了以推力需求为约束条件的暖机参数优化模型，实现了不同工况下最短暖机时间与转速的优化。

Aeroengine requires maintaining high rotational speeds for warm-up operations prior to takeoff; otherwise, thrust degradation may occur during the climb-out phase. To address this issue, this study focuses on a core engine of a small-bypass-ratio turbofan developing a Fluid-Thermal-Solid Coupling computational methodology that integrates a 1D fluid domain model with a 2D axisymmetric finite element model of the solid structure. This approach enables coupled simulation across different scales for solid domain analysis, air system evaluation, multi-component thermal analysis, and deformation prediction. Simulation results reveal that tip clearance exceeding design specifications constitutes the primary cause of thrust reduction during takeoff. Warm-up operations effectively reduce tip clearances, resulting in a 0.85% improvement in high-pressure turbine efficiency and a 0.5% enhancement in compressor efficiency. These improvements drive a maximum 0.51% increase in high-pressure rotor speed, aug-ment core mass flow, reduce engine bypass ratio, and ultimately elevate minimum takeoff thrust by 2.4%. Further analysis demonstrates that either extending warm-up duration or increasing warm-up rotational speed can enhance takeoff thrust. However, when the warm-up speed remains below 0.75, increasing rotational speed fails to effectively reduce high-pressure turbine tip clearance. Finally, leveraging sequential quadratic programming optimization, a warm-up parameter optimization model con-strained by thrust requirements is established to achieve optimal combinations of minimum warm-up time and rotational speed across various operational conditions.