用拉格朗日相关结构研究圆盘启动过程的流体输运

利用粒子成像测速(PIV)技术,得到了圆盘启动涡环流场的速度分布和涡量分布.圆盘启动涡环流场的有限时间李雅普诺夫指数场(Finit-time Lyapunov exponents,FTLE)以及拉格朗日相关结构(Lagrangian coherent structures,LCS)被计算出来.基于圆盘启动涡环流场的有限时间李雅普诺夫指数场以及拉格朗日相关结构,通过跟踪流体质点,对圆盘启动涡环流场的输运情况进行了分析.在圆盘启动涡环形成过程中,流体发现被圆盘和相互排斥的拉格朗日相关结构分成三部分.剪切流窗口(vorticity-flux window)被发现,涡量流通过剪切流窗口进入涡核.涡环的非定常边界被确定,它由相互排斥的拉格朗日相关结构背风面、圆盘以及剪切流窗口组成.

On the Fluid Transport In Disk Starting Process by Lagrangian Coherent Structures

Velocity distribution and vorticity distribution around vortex circulation field generated by disk starting were measured by using particle imaging velocimetry (PIV). The finite-time Lyapunov exponent (FTLE) field and the Lagrangian coherent structure (LCS) of the vortex flow were computed. Based on FTLE and LCS, following the tracks of a piece of fluid particles, fluid transport process of the vortex circulation field was analyzed. During the formation process of disk vortex circulation field, the fluid was found to be divided into three parts by the disk and the repelling-LCS. A vorticity-flux window was found through which the fluid with vorticity flows into the vortex core continuously and the unsteady boundary of the vortex ring which consists of the r-LCS leeward, the disk and the flux window was identified.