The Three-Dimensional Hydraulic Characteristics and the Impact of Layout Patterns in Air Cushion Surge Chamber During Load Change in Hydropower Stations

Air cushion surge chamber is an important facility for water hammer protection of hydropower station. However, the existing hydraulic transition process calculation basically adopts a one-dimensional model, which assumes that the water level in the air cushion surge chamber rises or falls as a whole, and ignores the three-dimensional complex flow patterns such as water gushing at the connecting pipe when load is dumped and water surface depression above the connecting pipe when load is increased, as well as its impact on the operation safety of hydropower station. In this paper, the one-dimensional hydraulic calculation model of hydropower station is established, and the inlet pressure fluctuation curve of the air cushion surge chamber is calculated as the three-dimensional calculation boundary condition. A local three-dimensional calculation model was constructed to simulate the dynamic changes of gas-water two-phase flow in an air cushion regulator. The accuracy of the model is verified by experimental data. The three-dimensional hydraulic characteristics of the air cushion pressure regulator are simulated and analyzed according to the three types of connection pipe layout, namely straight pipe, circular gradient section and inclined pipe. It is found that: when the load is discharged, the straight pipe will produce a violent water gushing in the gas room, forming a “surging spring area”, while the circular and gradual section type and the inclined pipe type can alleviate the violent water and gas movement in the gas room and eliminate the violent surge in the gas room. When the load is increased, the straight pipe connection pipe will cause the water level at the air chamber inlet to drop abruptly, forming a “drop zone”, and even empty leakage, while the other two layout types do not appear empty leakage phenomenon. The circular gradient section type and inclined pipe type connection pipe layout can alleviate or avoid severe gushing, water surface depression and other dangerous situations.