基于CFD/CSD耦合的叶轮机叶片失速颤振计算

为了研究叶轮机叶片的失速颤振特性,发展了一种计算流体力学与计算结构力学(CFD/CSD)时域耦合方法。该方法通过每一物理时刻CFD和CSD的循环迭代实现了耦合计算。在CFD分析中,采用鲁棒性较好的空间离散格式AUSM+-UP,并基于延迟脱体涡模型(DDES)模拟了带分离流动。在结构分析中,通过模态法构建了旋转叶片动力学方程并运用杂交多步方法进行求解。以孤立转子Rotor37为例,计算了不同工况下流场总体与细节参数,与实验结果的对比验证了CFD算法的精度。对某转子叶片进行了颤振特性研究,计算所得的广义位移时间响应曲线表明该叶片在近失速工况下会发生失速颤振,其表现形式为一阶弯曲模态发散且各阶模态之间不耦合。分析表明,流场不稳定和非定常效应是引起失速颤振的关键因素,同时折合频率的降低也会导致原本气动弹性稳定的叶片发生失速颤振。

Stall flutter computation of turbomachinery blade based on a CFD/CSD coupling method

A computational fluid dynamics/computational structural dynamics (CFD/CSD) model coupling in the time domain is developed for the stall flutter computation of turbomachinery blade. CFD and CSD slovers are coupled via successive iterations within each physical time step. In CFD analysis, a robust scheme named AUSM⁺-UP is adopted and delayed-detached-eddy simulation (DDES) is applied to simulating separated flow. In the structure analysis, the structural dynamic equation of rotating blade is constructed based on a modal approach and a hybrid multi-step scheme is used to solve the equation. The CFD codes calculate flow field characteristics of Rotor37 under different working conditions. The computed results show good agreement with the experimental results, both in overall performance and flow field details. The presented method is then applied to flutter computation and analysis of a test compressor rotor. The computed time response of generalized coordinates successfully predicts stall flutter at near stall condition and shows it to be a phenomenon of single bending-modal divergence and modal uncoupling. The results also indicate that the flow unstability and unsteadiness are key factors affecting the flutter characteristics. Besides, it is found that for the stable blade, the decrease of reduced frequency may cause stall flutter.