Experimental study on flow characteristics of pitching hydrofoil via stereo shadowgraph
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摘要: 为研究俯仰水翼引起的涡旋射流的流动特性，使用立体阴影成像系统对流场进行了三维测量。通过比较二维粒子图像测速、二维粒子追踪测速和三维粒子追踪测速的计算结果，发现刚性对称NACA0012翼型在静水中固定位置的纯俯仰运动会产生2个方向的弱射流，同时伴随产生小尺度涡旋。速度统计结果表明，当水翼旋转角较大时，会产生更为明显的涡旋及速度变化。本文研究得到了水翼俯仰运动产生的三维尾流结构，发现深度方向（z方向）上也存在关于z=−3 mm平面对称的涡结构。三维测量结果表明，在有限翼型纵横比下，不能忽略水翼俯仰运动产生的复杂三维流动深度方向的速度分量。Abstract: In order to study the jet flow characteristics caused by the pitching hydrofoil, a three-dimensional shadow imaging system is utilized to measure the turbulent flow field. By comparing the results of particle image velocimetry, two-dimensional particle tracking velocimetry and three-dimensional particle tracking velocimetry, it is found that the pure pitch motion of the rigid symmetric NACA0012 airfoil at a fixed position in the static fluid would produce weak jets in two directions, accompanied by the generation of small-scale vortices. The results of velocity statistics show that when the amplitude of the hydrofoil rational angle is large, more obvious vortex structure and velocity change are produced. The study obtained the three-dimensional wake structure generated by the pitching hydrofoil movement, and found that there is also a symmetric vortex structure in the depth direction. The results show that the velocity component in the depth direction generated by the pitching hydrofoil movement can not be ignored under the limited airfoil aspect ratio.
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Key words:
- velocity measurement /
- shadowgraph /
- 3D-PTV /
- pitching hydrofoil /
- vortex
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图 4 周期平均速度场和涡量场（工况1）
Figure 4. Periodic average velocity field and vorticity field of case 1
图 5 周期平均速度场和涡量场（工况2）
Figure 5. Periodic average velocity field and vorticity field of case 2
表 1 2种实验工况下的水翼运动参数
Table 1. Hydrofoil motion parameters under two experimental conditions
参数 数值 工况1 工况2 弦长c/mm 50 50 转动中心与前缘距离d/mm 5 5 最大旋转角θmax /（°） ± 10 ± 20 后缘最大速度ute /（m·s−1） 0.30 0.30 雷诺数Re 1.48 × 104 1.48 × 104 转动频率f /Hz 20 10 转动幅度a/mm 7.84 15.63 斯特劳哈尔数Sr 0.4994 0.4975 
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