实验研究具有周向抽吸轴对称射流的拟序结构

EXPERIMENTAL STUDY ON COHERENT STRUCTURES OF AXISYMMETRIC JETS WITH PERIPHERAL SUCTION

基于实验研究具有周向抽吸轴对称射流拟序结构的动力学行为，定义了临界出口主速度 以及超临界工况（低速工况）和亚临界工况．提出了超临界工况下，拟序结构的空间演化特征． 基于功率谱确定了超、亚临界工况流动系统发生自激励振荡的速度比范围．

This paper was aimed at the dynamical behaviors of coherent structures of axisymmetric jets with peripheral suction in the case of low forward velocities. According to the dynamical behaviors of the flow system, the critical forward velocity U_1～(cr) = 6.8m/s was defined, and consequently the supercritical regime U_1 < U_1～(cr) (U_1 denotes forward velocity) and the subcritical regime U_1 > U_1～(cr) respectively were also given. In the subcritical regime, the shear layer self-excited oscillation mode happens to the fluid system in a certain range of the velocity ratio R (R = (U_1 + U_2)/(U_1 - U_2), U_2 denotes suction velocity). In the supercritical velocity regime, the Kelvin-Helmholtz instability plays an important role and its spatial growth rate is increasing causing the formation and conglomeration of the axisymmetric vortices early accompanying with the increasing of the velocity ratio. When the first conglomeration of the vortices was completed, the vortex strengthens its intensity during a certain range of the space with its structure compacted and, as a consequent, the jet column happens to self-excited oscillation. When their intensities are saturated, the axisymmetric vortices are arranged in an ordered pattern within a certain range of the space causing the occurrence of the shear layer self-excited oscillation. In this papers the ranges of the velocity ratio for the occurrence of self-excited oscillation corresponding to the subcritical and supercritical regimes were also determined separately.