风扇叶片飞失显式动力学仿真网格与时间步长研究

Study on Mesh and Time Step of Explicit Dynamic Simulation for Fan Blade Out

为了研究大涵道比涡扇发动机风扇叶片飞失仿真中网格尺度与时间步长对于瞬态显式动力学分析结果的影响,采用有限元法中单元计算理论分析的方法分析了网格尺度和时间步长在计算稳定性方面的理论联系。采用多因素试验设计方法组织了针对叶片应力分布、转子轴心轨迹和支点外传振动应力3个风扇叶片飞失的典型输出参数的网格尺度和时间步长的影响研究方案,开展了典型物理过程、模型简化和数值计算无关性研究。针对时间步长为7×10^(-7)、5×10^(-7)、3×10^(-7)和2×10^(-7)s,网格尺度为40、30、20和15 mm的计算结果进行分析,结果表明:对于给定物理过程和目标时长,存在着网格尺度和时间步长的门槛值,如:2×10^(-7)s时间步长和30 mm网格尺度,超过该值进一步细化网格和减小时间步长对于精度提升不明显;显式动力学的计算原理决定了目标时间越长偏差累计越大,所需的网格精度就越高;碰摩过程对于风扇叶片飞失仿真的应力和外传振动偏差影响较大。

In order to study the influence of mesh scale and time step on the results of transient explicit dynamic analysis for the fan blade out simulation of high bypass ratio turbofan engine,the theoretical relationship between mesh scale and time step in computational stability was analyzed by using the method of element calculation theoretical analysis in finite element method.The multiple parameters test design method was used to organize the research scheme on the influence of mesh scale and time step of three typical output parameters of fan blade out,including blade stress distribution,rotor axis trajectory and transmitted vibration stress outside the fulcrum.The research on the independence of typical physical process,model simplification and numerical calculation was carried out.The calculation results with time step of 7×10^(-7)、5×10^(-7)、3×10^(-7)and 2×10^(-7)s and mesh scale of 40、30、20、15 mm were analyzed.The results show that for a given physical process and target time,there are threshold values of mesh scale and time step,such as 2×10^(-7)s time step and 30 mm mesh scale.Beyond this value,further refining the mesh and reducing the time step are not obvious for the improvement of accuracy.The calculation principle of explicit dynamics determines that the longer the target time is,the greater the deviation accumulation is,and the higher the mesh accuracy is required.The impact and wear process has a great influence on the stress response and vibration transmission of fan blade out simulation.