Author(s): Pfister Michael; Hager Willi H.; Minor Hans-Erwin
Keywords: Erator; Air Concentration; Chute; Deflector; Offset; Spillway 1
Abstract: Chute aerators are applied when cavitation damage is expected or observed on spillways. The design of these aerators is based on current literature describing the efficiency of aerators mainly with a global air entrainment coefficient. This coefficient is related to the average air transport of the two-phase flow downstream of the aerator, which has to exceed a certain limit for an acceptable cavitation protection. Because cavitation occurs near the chute boundaries, the air transport close to the chute bottom is of prime interest. The present study investigates the development of the air transport along the jet caused by the chute aerator and the flow downstream of the re-attachment point. Experiments were performed on a VAW model to measure the local air concentrations in the near-field of chute aerators. Three regions were defined to describe typical flow conditions in terms of the water surface, the jet thickness, the average air concentration, the bottom air concentration and the minimum air concentration. It was found that aerators primarily increase the average air concentration. The bottom air concentration, in contrast, is only slightly increased to a maximum of 4% beyond 5 times the jet throwing length. As is typical for two-phase flow, the bottom air concentration corresponds to the minimum air concentration over the whole flow depth downstream of the jet re-attachment point. The quality of the current data is also discussed with regard to scale effects.