Abstract
The flow around the ramp embedded in a pressurized tunnel is divided into various zones downstream of the ramp, including the cavity and the main zone of flow above the shear layer. Ramp angle and height are parameters that affect the flow characteristics such as cavity length, velocity, and pressure coefficient immediately downstream of the ramp. In this study, OpenFOAM open source software and RNG K-ε turbulence model were used to simulate the flow around the under pressure tunnel ramp. In order to investigate the effect of the ramp geometry on the flow in various relative air discharges 0<β<10, the range of height and the angle of the ramp as 5<θ<20 and 0.1<tr/d<0.4 were developed and simulated. The correlation coefficient between the numerical and experimental results for the relative cavity length is in the range of 0.9377≤R2≤0.9722 that indicates proper agreement between results. The result of the research shows that in both cases of fixed height of ramp and increasing ramp angle, and fixed angle of the ramp and increasing ramp height, the values of the cavity length and maximum turbulence intensity increase, and the minimum pressure values at the cavity zone bed are decreased. But in both cases, the sensitivity of the three mentioned parameters is higher than the ramp height increment.
Highlights
Aeration is known as the most efficient and economical method for prevention of cavitation in high-speed flows over chute spillways [1, 2]
Surface aeration takes place in spillways but in this way usually not enough air is introduced near the concrete surface [5]
The flow near the aerator ramp embedded in a under pressure flow in various values of relative air discharge β, 0≤β≤10, angle θ, 5o≤θ≤20o, and height tr, 0.1≤tr/d≤0.4 were simulated until the effect of θ and tr on the characteristics of the flow, such as the cavity length (LC), the minimum values of the pressure at the cavity zone bed (CPmin) and maximum turbulent intensity (T.I.max) were determined immediately downstream of the ramp
Summary
Aeration is known as the most efficient and economical method for prevention of cavitation in high-speed flows over chute spillways [1, 2]. With 8% air near the concrete surface the damage of cavitation attack is completely prevented [3, 4]. Surface aeration takes place in spillways but in this way usually not enough air is introduced near the concrete surface [5]. Aerators cause the flow to separate from the surface of the spillway and form a nappe. The entrainment on the lower surface introduces air bubbles near the bed of the spillway for some distance downstream [8, 9]
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