Turbulent lock release gravity current

The time evolution of a turbulent lock release gravity current, formed by a finite volume of homogeneous fluid released instantaneously into another f luid of slightly lower density, was studied by experimental measurements of the density structure via elaborate digital image processing and by a nume rical simulation of the flow and mixing using a two-equation turbulence mod el. The essential fact that the gravity current passes through an initial s lumping phase in which the current head advances steadily and a second self -similar phase in which the front velocity decreases like the negative thir d power of the time after release is satisfactorily presented by the labora tory observation. An overall entrainment ratio proportional to the distance from the release point is found by the numerical simulation. The renormali zation group (RNG) k - epsilon model for Reynolds-stress closure is validat ed to characterize the gravity current with transitional and localized turb ulence.