Mechanical energy loss and Rayleigh-Taylor instability in free discharge of vertical sharp-edged orifices

Orifice discharge is a classical hydrodynamic phenomenon. The experiments of liquid free jets through vertical sharp-edged orifices were conducted on the influences of orifice geometry and liquid depth. The flow mechanism indicates that the higher energy loss of thin-walled orifice is caused by the inspired air annulus inside orifice channel which will lead to the Rayleigh-Taylor instability. The theoretical derivation further demonstrated that the consecutive collisions between main stream and surface waves can cause significant energy dissipation. Besides, a kind of transition orifice was found for the first time: the increase of liquid depth can induce a sudden switch from the thick-walled orifice mechanism to the thin-walled one. The presentation in this work on the formation and development of coherent structures, the migration and bursting of vortexes, as well as the interaction between vortexes and free interface, is universal for revealing the essential features of multi-phase flow in form friction.