First and second force peaks generated by a surge impact on a wall with and without overtopping

Abstract

This paper presents a study of dam-break induced surges impact on a wall carried out with a compressible two-phase RANS model. The parameters varied are the reservoir fill height and the wall height. The focus is here on the first and second force peak occurring during the impact and especially their relative magnitude. With an infinitely high wall, the simulations reveal that both, the first and the second peaks increase with the water height in the reservoir and that the second peak is always larger than the first one. The increase of the surge momentum explains the gradual augmentation of both peaks. The second peak being larger than the first is due to the interdependency of both impact phases and the key role of the surge momentum in controlling this dynamics. The non dimensional analysis conducted on these cases, shows that the force peaks increase with the surge Froude number. Nevertheless, it is difficult to relate a specific case to a given Froude number, due to the flow unsteadiness. When the height of the obstacle is finite, the overtopping do not change the first force peak on the front wall face but significantly reduces the magnitude of the second one. Additionally, the maximal horizontal force on the wall, accounting for the force on rear wall face, occur at the beginning (i.e., during the first peak) or at the end of the impact process (i.e., during the second one) depending on the overtopping volume allowed.