Baigiamajame magistro darbe nagrinėjamos pneumatinių bei mechaninių aeravimo sistemų problemos, jų konstrukcijos. Taip pat išnagrinėti veiksniai įtakojantys aeratorių efektyvumą. Išnagrinėjus konstrukcijas pasirinkti 3 aeratoriai su kuriais atlikti eksperimentai bei įvertintas jų efektyvumas. Darbą sudaro 8 dalys: įvadas, tyrimo objektas ir problemos aprašymas, tiriamųjų aeravimo sistemų apžvalga bei konstrukcijų analizė, mechaninių ir pneumatinių aeravimo sistemų efektyvumo analizė, tyrimo metodika bei eksperimentinis stendas, tyrimo rezultatai, išvados, literatūros sąrašas. / The following masters work consists of the analyse of the pneumatic and mechanical aeration systems, these problems and construction. Also explored factors who does influence for the efficiency of the aerators. When the constructions were explored, 3 aerators were selected, the experiments was made and valuated the efficiency. There are 8 chapters: introduction, the object of the analys and description of the problem, review of the explored aeration systems and analys of the constructions, efficiency analysis of mechanical and pneumatic aeration systems, methodology of the analysis and case of the experiment, results of the analysis, conclusions and suggestions, the list of the literature.

Due to the high-speed flow in a chute spillway, cavitation damages often occur. This undesired phenomenon threatens the safety of the structure. For the purpose of eliminating the damages, an aerator is often installed in the spillway. To understand its characteristics, physical model tests are a popular method. To complement the model tests, computation fluid dynamics (CFD) simulations are used to study aerator flows. To represent the two-phase flows, multiphase models should be employed. This thesis examines two of them, namely, the Volume-Of-Fluid model (VOF) and Two-Fluid model. Based on the background of the Bergeforsen dam, the aerator flow is modelled by means of the VOF model. The simulated spillway discharge capacity is in accordance with the experimental data. Compared with the results, empirical formulas fail to evaluate the air supply capacity of aerator as it is wider than the conventional width. A hypothetical vent modification is proposed. For the original and proposed layouts, the study illustrates the difference in the air-flow conditions. The results show that a larger vent area is, for a large-width aerator, preferable in the middle of the chute. To study the flip bucket-shaped aerators in the Gallejaur dam, physical model tests and prototype observations are conducted. The results lead to contradicting conclusions in terms of jet breakup and air entrainment. A CFD model is, as an option, employed to explain the reason of the discrepancy. The numerical results coincide with the prototype observations. The jet breakup and air entrainment are evaluated from air cavity profiles; the air-pressure drops are small in the cavity. The discrepancy is due to overestimation of the surface-tension effect in the physical model tests. Based on the experimental data of an aerator rig at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW), ETH Zurich, the Two-Fluid model is used to predict air concentration distributions in the aerated flow. The model includes relevant forces governing the motion of bubbles and considers the effects of air bubble size. The numerical results are conformable to the experiments in the air cavity zone. Downstream of the cavity, the air concentration near the chute bottom is higher, which is presumably caused by the fact that the interfacial forces in the Two-Fluid model are underestimated. / <p>QC 20170224</p>