开闸式异重流锋速转变的一个判据
摘要
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.