Force effects of the flow on energy absorbers in the presence of cavitation

Abstract

As the experience of operating high-pressure spillway structures shows, the operating conditions of the downstream extinguishing devices are very difficult. At flow rates, more than 12–15 m/s, downstream damping devices, as a rule, operate in a cavitation mode. First of all, this mode of operation gives rise to erosional destruction of the damper itself and the waters near it. This occurs where the cavitation torch closes on the structure. Attempts to avoid these desirable phenomena by lining erosion sites with steel sheets do not always lead to the desired result since it is not uncommon for the steel lining to be torn off by hydrodynamic forces. The separation of the cladding occurs in two cases: firstly, when the cladding is not in close contact with the concrete to be protected, and secondly, its anchoring is not enough. In both cases, fracture occurs from fatigue phenomena in the metal due to multiple oscillatory cycles from hydrodynamic loads. It is difficult to avoid this in cavitation modes since the spectrum of pressure pulsations, in this case, is very wide, which leads to oscillations of linings at resonant frequencies. Apparently, the strength of the linings is an object of special research, and in the future, it should be dealt with theoretically and experimentally. Hydrodynamic forces at high flow rates in the zone of intense energy extinguishing can reach such values that they can lift and overturn concrete slabs of water walls and water walls. Currently, there are practically no specific and accounting for vertical hydrodynamic loads on slabs of water walls in the presence of cavitation on erosion-free absorbers in the technical literature. To a certain degree of approximation, it is possible to use experimental data obtained on a model of the same structure but operating without cavitation, as data on hydrodynamic loads in the downstream of structures operating in a cavitation mode. The main disadvantage of such comparisons is that there is no guarantee that the amplitude and frequency characteristics of the flow during cavitation do not change (in particular, the amplitudes do not increase) as the cavitation limit is approached.