低旋流数旋进射流流动特性的PIV实验研究

采用粒子图像测速技术，研究了当雷诺数Re=4.5×104时低旋流数旋进射流的流动特性。针对3种不同旋流数（S=0、0.26和0.41），对比分析了时均流向速度场、流向速度脉动强度场以及时均涡量场的变化规律。实验测量结果表明:随着旋流数的增加，流向速度大小及其脉动强度沿流向衰减加剧，而射流中心线上的速度脉动强度增强；因腔体壁面空间限制而产生的回流区向上游移动且尺度变小；外剪切层中旋涡的流向发展急剧衰减而内剪切层内的旋涡几乎不受影响。此外，结合速度谱和典型时刻的瞬态流场特征可知，旋流数增大后，旋进频率增大，而旋进现象发生的起始位置向上游移动，使得旋进偏转角度增大。

PIV experimental study on flow characteristics of a low swirl number precessing jet

This study focuses on the flow characteristics of a low swirl number precessing jet at Reynolds number Re=4.5×104 using particle image velocimetry (PIV). The time-averaged streamwise velocity fields, streamwise velocity fluctuation intensity fields and time-averaged vorticity fields at three swirl numbers, i.e., S=0, 0.26 and 0.41, respectively, are compared and analyzed. The experimental results show that as the swirl number increases, the attenuation of the streamwise velocity and its fluctuation intensity increase along the streamwsie direction, the velocity fluctuation intensity on the jet centerline increases, the recirculation zones caused by the confinement move upstream with their scales decreasing, and the streamwise development of the vortex in the outer shear layer decays rapidly, while that in the inner shear layer is almost unaffected. In addition, combining the streamwise velocity spectrum and the characteristics of the transient flow field at a typical time, it can be seen that as the swirl number increases, the precession frequency increases, and the starting position of the precession phenomenon moves upstream, which increases the precession deflection angle.