Prevention of air-entrainment at the outlet of a pumped storage plant – large scale model tests

To avoid the generation of air-entraining vortices at a projected outlet structure in an existing reservoir of a pumped-storage plant, large-scale model tests were conducted. The model, with a scale of 1:18, had the considerable dimensions of 30 m in length and 16 m in width. Due to the complex shape of the reservoir, the many inlets and outlets, and numerous operating conditions, very complex flows occurred. Depending also on the water level, the direction of flow approaching the outlet was always changing. This made it hard to find a solution for all operating conditions and water levels that avoided air-entraining vortices. However, with the suggested measures it was possible to maintain operation down to a quite low drawdown level without airentrainment.