离心叶轮气动阻尼的数值分析

Numerical analysis of aerodynamic damping for centrifugal impeller

为进行运动边界下离心叶轮流场的数值分析,独立开发了网格变形程序和非定常流动分析程序,实现了流场中振动离心叶轮的气动阻尼计算。采用紧支撑径向基函数法进行结构到气动表面变形的数据传递,应用二叉树技术进行壁面距离的计算,大幅提高了网格变形和流场分析中距离搜索的计算效率。通过振动叶栅和离心叶轮的算例,验证了程序应用于运动边界流场计算和叶轮流场模拟的正确性。以某离心叶轮为对象,展开其模态气动阻尼比的计算分析。结果表明:考察的两个模态下气动阻尼比均为正值,小幅振动下模态气动阻尼比与振幅无关,轮盘振动模态下叶轮的气动阻尼比随工况接近失速而逐渐减小。

In order to carry out the numerical analyses of the flow fields with moving boundaries in centrifugal impellers,the codes for the grid deformation and the unsteady flow simulations were developed independently,by which the calculations of the aerodynamic damping of centrifugal impellers were realized.By adopting the compactly supported radial basis function to carry out the data transfer of surface deformation from the structure mesh to the flow mesh,and utilizing the binomial tree technique to fulfill the wall distance calculations,the computation efficiencies of grid deformation and flow-field analyses were greatly increased.According to the test cases of an oscillating cascade and a centrifugal impeller,the correctness of the code for the simulations of the flow-fields with moving boundaries and the flows in centrifugal impellers was validated.Then taking a centrifugal impeller as the research object,the calculations of modal aerodynamic damping ratios were carried out.Results showed that,the aerodynamic damping ratios of two selected modes were both positive.The modal aerodynamic damping ratio had no relationship with the oscillating amplitude under small oscillations.For the disk vibration mode,the value of aerodynamic damping ratio decreased as the operating condition shifted towards the stall point.