淹没射流湍流场的TR-PIV测量及流场结构演变的POD分析

TR-PIV measurement of the turbulent submerged jet and POD analysis of the dynamic structure

利用平面激光诱导荧光流动显示技术(LIF)和二维高速粒子图像测速技术(TR-PIV)对淹没射流和自由面相互作用湍流场进行了细致的测量,并利用本征正交分解方法(POD)对测得的流场进行分解,提取流场中含能大尺度结构并分析其与自由面相互作用特点。射流出口雷诺数Re=5600,淹没深度H/D=4。LIF实验结果表明:自由液面的存在使得射流在向下游扩散发展中存在向上运动的趋势。时均流场也表明射流上半部分扩散速率更快,在相互作用区域,最大速度位置逐渐向自由液面靠近,类似自由射流的流向湍流度双峰值分布形式随流向距离增大而逐渐消失。POD分解得到的空间模态表明:射流中有序的相干结构在上游逐渐发展,随后迅速向上发展并与自由液面发生相互作用,在下游,由于自由液面的限制,大尺度结构又开始向下发展。

The flow field of a submerged turbulent jet interacting with a free surface was measured using laser-induced fluorescence and time-resolved PIV techniques,and the dynamics of the flow structures were examined further using the proper orthogonal decomposition （POD）a-nalysis technique.The jet axis was located at the depth of H/D =4 below the free surface and the Reynolds number was 5600.The LIF results show that the jet flow exhibits an upwelling motion due to the existence of the free surface.The time-averaged flow field shows that the upper half portion of the jet flow spreads faster and the maximum velocity is located towards the free sur-face.The typical off-axis double peaks distribution of stream-wise turbulent intensity disappears as the downstream distance increases.The POD results show that the upstream well-organized coherent structures rise up rapidly when the jet is about to approach the free surface and the sub-sequent strong interaction occurrs.The dominant large-scale structures begin to develop down-ward in the further downstream due to the confinement in the vertical direction.