A STUDY OF THE MECHANISM OF VORTEX BREAKDOWN

涡破裂的特点是有三种破裂形式，在涡轴上有一个滞止点，振荡速度的频率显著。我们提出了一个分析模型来解释这些所有功能一致的想法下，任何波长的小速度扰动躺在一定的区域将被放大，不稳定的速度将产生声流。通过对三种涡破裂的稳定性和速度场的分析，比较了三种涡破裂的条纹线与流场的关系，并利用可视化技术对三种涡破裂形式：气泡型、螺旋型和双螺旋型进行了观察。激光多普勒测速仪测量上游和气泡类型的破裂尾流。给出了回流区内外的脉动速度谱、时均旋流和轴向速度分布， 关于我们 区，已获得。对实验数据的频谱分析表明，在稳定回流区，振荡速度的显著频率是恒定的，为了证实扰动的方位波数决定击穿类型的观点，我们制作了一个旋转波发生器（SWG），它是一种在特定频率下产生沿周向旋转的正弦波扰动的装置。SWG由四个活塞组成，它们在附接到测试管壁的气缸中操作，并产生四种旋转正弦波扰动：四个方位波数m = 0，+1，-1，2。对旋流施加四种不同方位波数的正弦波，研究了旋流破裂类型和位置的转变过程。结果表明，m = 0、+1和2的正弦波扰动分别产生空泡、螺旋型破裂和双尾空泡或扁平空泡。少

The features of the vortex breakdown are that there are three types of breakdown, and it has a stagnation point on the vortex axis and the prominent frequencies of oscillating velocities. We presented an analytical model to explain these all features consistently under the idea that the small velocity disturbances of any wave length lying within a certain region would be amplified and unsteady velocity would produce acoustic streaming. We analyzed the stability and the velocity fields, and compared the calculated streak lines with the observed flow pattern for the three types of vortex breakdown.The three types of vortex breakdown were observed in water flows through a straight pipe by a visualization technique : bubble, spiral and double-helix types. Laser-Doppler velocimeter measurements upstream and in the wakes of breakdown of bubble type are described. Spectra of the fluctuating velocities, as well as timeaveraged swirl and axial velocity profile both inside and outside the recirc … More ulation zone, have been obtained. Spectral analysis of the data indicates that the prominent frequencies of oscillating velocities are constant in the steady recirculation.We made a spinning wave generator(SWG), which is a device to produce, at a specified frequency, a sinusoidal wave disturbance spinning in the circumferential direction, in order to confirm the idea that the azimuthal wave number of the disturbance would determine the type of breakdown. SWG is composed of four pistons, which operate in the cylinders attached to the test pipe wall, and creates four kinds of spinning sinusoidal wave disturbances : four azimuthal wave numbers m = 0, +1, -1, 2. The four kinds of sinusoidal waves with azimuthal wave number were imposed to the swirl flow and the transition process of the breakdown type and location was investigated. It was shown that the m = 0, +1, and 2 sinusoidal wave disturbances produce the bubble, spiral type breakdown, and two-tailed bubble or flattened bubble respectively. Less