Study On Hydraulic Characteristics Of Sudden Expansion And Expansive Aeration Facilities

There is abundant hydropower resources varied in types, including many rivers and with long coastline in our country. China’s water conservancy and hydropower is developed very fast with the successive emerging of the drainage buildings, pumping stations, high head hydropower station in resent years since reform and opening up. The issues of high-speed flow are often encountered in the design, construction and scientific research of high head hydraulic structure and these issues are range from the considered phenomenon of cavitation and erosion in local place to the key point which has influence on become the normal work of the whole hub, power station and pump station. To reduce the cavitation erosion by aeration facilities has become one of the most effective means that has been proved by a large number of engineering practices both at home and abroad. While different aeration facilities have different body types with different aeration effect and the different use fields. The sudden lateral enlargement and sudden drop aeration facilities are discussed and analyzed in this paper.The hydraulic characteristics within the sudden expansion and drop aerator are studied by the hydraulic model test in this paper and the control variable methods are used in order to improve the inlet efficiency of aeration facilities. The different combinations of aeration facilities are formed by changing the height of the sudden drop and the width of the sudden enlargement, and various factors include the change rule of the gas concentration under different solutions and conditions, influence elements, the relationship between bubble and gas concentration, the sensitive factors of the of the aeration cavity length and the pressure distribution characteristics of the bottom and side wall are analyzed by changing the flow.Some conclusions are obtained by the combination of the model tests and theoretical analysis:1) The gas concentration is a single peak along the route via the study of the change rule of long-term concentration in different sections and different depths along the route. The maximum value appears on the surface while the minimum appears in the middle before the peak in different depths and just contrary after the peak. The distribution of the two sides is symmetric and greater than the middle part in different sections.2) Flow, sudden drop height and the sudden enlargement width which mainly affect the gas concentration are studied to draw the conclusion that all the three factors have the relationship of positive correlation with gas concentration.3) The more small size bubbles are, the larger the gas concentration is and the distribution rule of small bubbles is the same with the flow aeration concentration.4) Flow, sudden drop height and the sudden enlargement width are the main elements that influence aeration cavity length but these factors have different sensitivity to bottom cavity length and lateral cavity length. For the flow, the sensitivity of the two lengths is almost the same and the bottom cavity length is sensitive to the changes of the sudden drop height while the lateral cavity length is sensitive to the sudden width.5) The turbulent pressure value is about 0.5 times as the time average pressure on the bottom plate, the pulse pressure value of side walls impact area is off from the normal distribution while the pulse pressure value of stable region is tending to the normal distribution.