Modal Analysis of a Laminar-Flow Airfoil under Buffet Conditions at Re = 500,000
Modal Analysis of a Laminar-Flow Airfoil under Buffet Conditions at Re = 500,000
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DOI：
10.1007/s10494-019-00087-z
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发表时间：
2019-12
期刊：
影响因子：
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通讯作者：
M. Zauner;N. Sandham
中科院分区：
文献类型：
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作者：
M. Zauner;N. Sandham
跨音速颤振的翼型表现出非定常激波和边界层现象的复杂组合，预测模型是不足的。最近使用湍流模型应用计算流体力学方法的方法似乎很有前途，但仍然无法回答有关抖振详细机制的一些基本问题。本文的贡献是基于层流翼型在马赫数M= 0.7时和中等雷诺数Re= 500000下跨音速抖振的直接数值模拟。在迎角为α= 4∘时，附面层稳定性随翼型气动载荷的变化有显著变化。除了开尔文亥姆霍兹不稳定性，还可以识别出一种整体模式，它显示了耦合的声学和流分离动力学，与文献一致。这些模式也存在于非定常直接数值解的动态模式分解(DMD)中。此外，在Strouhal数为ST= 0.12时，DMD获得了与实验一致的自振模式。与平均流的全局稳定性分析相比，DMD分析对流量波动的重建更加完整和稳健。将攻角从α= 3∘增大到α= 4∘，对应于C型激波运动的DMD模的强度增加。一个重要的观察结果是，在本例中，跨音速抖振与激波运动没有直接耦合。
An airfoil undergoing transonic buffet exhibits a complex combination of unsteady shock-wave and boundary-layer phenomena, for which prediction models are deficient. Recent approaches applying computational fluid mechanics methods using turbulence models seem promising, but are still unable to answer some fundamental questions on the detailed buffet mechanism. The present contribution is based on direct numerical simulations of a laminar flow airfoil undergoing transonic buffet at Mach numberM= 0.7 and a moderate Reynolds numberRe= 500, 000. At an angle of attackα= 4∘, a significant change of the boundary layer stability depending on the aerodynamic load of the airfoil is observed. Besides Kelvin Helmholtz instabilities, a global mode, showing the coupled acoustic and flow-separation dynamics, can be identified, in agreement with literature. These modes are also present in a dynamic mode decomposition (DMD) of the unsteady direct numerical solution. Furthermore, DMD picks up the buffet mode at a Strouhal number ofSt= 0.12 that agrees with experiments. The reconstruction of the flow fluctuations was found to be more complete and robust with the DMD analysis, compared to the global stability analysis of the mean flow. Raising the angle of attack fromα= 3∘toα= 4∘leads to an increase in strength of DMD modes corresponding to type C shock motion. An important observation is that, in the present example, transonic buffet is not directly coupled with the shock motion.