近失速形态下冰脊分离非定常流的IDDES和模态分析

Unsteadiness and Modal Analysis of Ridge Ice-Induced Separation in Post-Stall Conditions via IDDES

采用改进延迟脱体涡模拟(IDDES)方法,对近失速条件下溢流冰脊诱导的剪切层振荡现象进行高分辨率模拟,描述高雷诺数下冰脊分离流大尺度分离的流场演化特征.研究表明,近失速形态下,冰脊和下翼面尾缘同时诱导出剪切流动,冰脊诱导的剪切层并未再附到壁面,与下翼面上洗流动相互干扰,形成大尺度低能态结构.结合频谱分析进一步发现,剪切层内的压力脉动存在两种典型的脉动频率,与Kelvin-Helmholtz不稳定性相关,具体表现为涡配对和涡脱落.基于正交分解得到的压力脉动主导模态为剪切层之间的大尺度相干结构.主导模态的时间系数与升力系数的功率密度谱峰值保持一致,这说明尾缘区大尺度相干结构与升力波动具有相关性.

High-resolution simulation of shear layer oscillation induced by ridge ice in post-stall condition is conducted via the improved delayed detached-eddy simulation(IDDES)method.The flow-field evolution characteristics of large scale separation in high Reynolds number condition are described.It is shown that the ridge ice and trailing edge of the lower surface induce the development of shear flow at the same time.The wall is not reattached by the shear layer induced by ridge ice,and the“up-wash”flow from the lower surface is interacted with the shear layer,which lead to the formation of large-scale coherent structures.Combined with the spectral analysis,the pressure pulsation located in the shear layer is characterized by two typical frequencies,which are associated with Kelvin-Helmholtz instability and appear as the vortex pairing and shedding.Based on the proper orthogonal decomposition,the dominant mode of pressure pulsation between shear layers is extracted as large-scale coherent structures.The same peak value is shown in power density spectrum of dominant mode temporal coefficient and lift coefficient,which indicates that the large-scale coherent structure is connected with lift fluctuation.