【摘要】 异重流是两种流体因密度差异产生的流动,是自然和工业生产部门中常见的现象.开闸式异重流是异重流研究的常用和典型模型.本文利用时间解析粒子图像速度仪(TR-PIV)测量了水槽中的开闸式异重流流场.实验中观察到异重流传播过程中从锋速,即头部速度为常数的初始坍塌阶段进入到锋速按时间的-1/3次幂递减的自相似阶段时,水平流速的速度剖面会发生振荡现象.该振荡是由开闸时传至左端壁而反射的波动引起的.这种振荡现象可作为开闸式异重流锋速转变的一个判据.更多还原

【Abstract】 Gravity currents, which occur whenever fluid of one density flows primarily horizontally into a fluid of different density, are widespread in natural and industrial systems. Experimental results for lock-exchange gravity currents in a channel of rectangular cross-section are presented. High-speed particle image velocimetry and laser-induced fluorescence in refractive index-matched gravity currents were used to study the spatial and temporal resolution of flow structures. As previously reported, the resulting gravity current, if viscous effects are negligible, passes through two distinct phases. The transition from the first to the second phase is observed to be rather abrupt and occurs when a disturbance generated at the endwall overtakes the front. We discover that the streamwise velocity profiles oscillate during this short stage. Furthermore, the relevance between the oscillation and the disturbance are discussed. This oscillation phenomenon can be used as a criterion for the transition of the front velocity in lock-exchange gravity currents.更多还原