Numerical analyses of flow characteristics in the vicinity of spillway aerators

Kurt, Can
Spillway aerators are used in the spillways that are designed to carry medium to high discharges during their operation. Aerators are aimed to reduce the risk of cavitation in these high velocity flows. Most of the time, design of these aerators are based on physical models and experimental results. However, with the advancement in computational resources, it became possible to analyze the effect of aerators using computational fluid dynamics (CFD). To this end, three-dimensional numerical simulations of such flows are conducted using finite-volume techniques. In this study the k-ε model is used for turbulence closure and the air-water interface tracking is made possible using Volume of Fluid (VOF) method. The aim of the study is to quantify the effect of submerged circular aerators located at the bottom of a stepped spillway to the flow structure in general. A single sloped (tan(θ)=0.3) spillway with single step is considered in the study. The flow enters the step over a small ramp called a deflector. The ramp angle is considered as one of the variables in the test cases. Two different ramp angles are considered and the results are compared to a step without any ramp. Discharge of the flow over the spillway, the aerator number, size and position with respect to one another, Froude number are considered as other variables in the study. The jet-length, amount of air-entrainment, average flow structure after the step are investigated. Through numerical simulations a direct relation between jet-length and 1.75 Fr is observed. Varying the location of the aerators over the step do not change the overall aeration significantly. However, larger diameter aerators that are placed closely together might affect the air concentration near the channel bed. A logarithmic decay of air concentration in the streamwise direction after the reattachment point is observed through simulations.


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Citation Formats
C. Kurt, “Numerical analyses of flow characteristics in the vicinity of spillway aerators,” M.S. - Master of Science, Middle East Technical University, 2016.