Coherent structures in the wake behind a trailing edge cutback
Coherent structures in the wake behind a trailing edge cutback
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后缘缩减后尾流中的连贯结构
DOI：
10.1016/j.expthermflusci.2018.02.021
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发表时间：
2018-06
影响因子：
3.2
通讯作者：
Dai Ren
中科院分区：
文献类型：
--
作者：
Shi Liu Liu;Yao Shi Chuan;Dai Ren
本文通过实验研究了冷却剂喷射对尾缘切缝后非定常尾迹气动特性的影响。采用高分辨率平面粒子图像测速（PIV）系统对雷诺数Re h= 2000时的流场进行了详细测量。对比分析了时均速度场、回流区速度和速度亏损的分布，以及流向雷诺应力和切应力的等值线，揭示了冷却剂喷射对尾流气动性能的影响。采用本征正交分解（POD）方法对速度场进行分析，揭示了拟序结构的演化过程以及冷却流与主流的混合过程。在低阶模态中识别出从唇板和下板脱落的大尺度相干结构，表明这些是尾流中最具能量的结构。此外，对于较低的吹气情况（VR= 0.5和0.75），在不成对的第三本征模中发现了“条带”结构。通过前六阶模态的POD滤波，观察到了下板上剪切层分离后的拍动运动。相干结构被识别出的旋涡强度的轮廓。分析认为，分离剪切层的“条”状结构和扑动是涡并合的结果，即两个顺时针旋转的涡结构从唇板和下板的上剪切层脱落并合。
An experimental study was performed to investigate the influence of coolant ejection on the aerodynamic characteristics of the unsteady wake behind a trailing edge cutback. A high-resolution planar particle image velocimetry (PIV) system was emlpoyed to conduct detailed flowfield measurements at a Reynolds number of Re h= 2000. The time-averaged velocity fields, the distributions of reverse-flow intermitteny and velocity deficts were comparatively studied, and contours of streamwise Reynolds stress and shear stress were examined to disclose the influence of coolant ejection on wake aerodynamic performance. Proper orthogonal decomposition (POD) ananlysis was applied to the velocity flowfileds to disclose the evolution of coherent structures and the mixing process between the cooling stream and mainstream. Large scale coherent structures shed from both the lip and lower plates were identified in low-order modes, indicating that these are the most energtic structures in the wake. Moreover, a “strip” structure was found in the unpaired third eigemode for lower blowing cases (VR= 0.5 and 0.75). By POD filtering with first six eigenmodes, the flapping motion of the separated shear layer from the upper shear layer of the lower plate was observed. Coherent strucutres were identified from the contours of swirling strength. It is speculated that the “strip” structure and the flapping of the seprarated shear layer is resuled from vortex merging, ie, the merging of two clockwise-rotating vortical structures shed from the upper shear layers of the lip and lower plates.
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