Experimental study on flow characteristics of pitching hydrofoil via stereo shadowgraph

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.