Author(s): Benjamin Hohermuth
Linked Author(s): Benjamin Hohermuth
Keywords: Air-water flow; High-head outlets; Phase-detection probe; RANS model;
Abstract: High-velocity flows typically feature air entrainment. While air-water flows on spillway chutes have been well examined, information on air-water flow in mildly to moderately sloped channels typically encountered in high-head outlet structures is scarce. Therefore, physical model tests and numerical simulations were used in this study to improve the understanding of high-velocity air-water flows downstream of a high-head sluice gate. The effect of different inflow conditions such as contraction Froude number on the air concentration distribution was experimentally investigated. Shockwaves and strong splashing dominated the longitudinal development of the depth-averaged air concentration close to the gate, whereas air entrainment further downstream was governed by the turbulent boundary layer reaching the free surface. The obtained data provide novel insights into high-velocity air-water flows and were also used for the evaluation of a numerical model. A Reynolds-averaged mixture model approach was used to simulate the flow conditions observed in the hydraulic model. The simulated mixture surface and air concentration profiles showed an overall good agreement with the measurements. However, close to the gate significant deviations were observed due to the inability of the model to simulate drop formation. This demonstrates that the numerical model was only able to capture the air entrainment process driven by the turbulent boundary layer reaching the free surface. Overall, the general knowledge on air-water flows downstream of high-head sluice gates was advanced and the capabilities and limitations of numerical simulations of such flows were demonstrated.