Large eddy simulations of ventilated micro-hydrokinetic turbine and pump-turbines

Abstract

Large eddy simulations of ventilated hydrokinetic turbine and pump-turbine are conducted. The mathematical modeling of oxygen dissolution and the flow model employed were validated by comparing predicted dissolved oxygen concentration against reported experimental measurements. A parametric study is performed to investigate the influence of interfacial forces, surface tension and bubble breakage and coalescence terms. It is demonstrated that aeration via hydrokinetic turbines can be used to improve the dissolved oxygen level in rivers for better water quality. It is also shown that aeration can effectively be achieved via the pump-turbine system to provide the desired dissolved oxygen level for the microorganisms’ growth during the wastewater treatment process. Air injection is applied to the wake region of each unit. The influence of aeration on the turbine performance, flow induced vibration and oxygen dissolution characteristics are investigated. The numerical predictions reveal that the aeration can be utilized in both hydro systems without experiencing a significant penalty in power generations. Aeration significantly reduces the flow induced vibration in the pump turbine system. The pressure pulsation on the draft tube surface of the pump-turbine is reduced significantly with both central and peripheral aeration. In hydrokinetic turbine, the variation in the standard deviation of power, which is related to the vibration of the turbine unit, is strongly dependent on the turbine operating conditions. Draft tube aeration provided 30% greater amount of dissolved oxygen and 3.2 times higher dissolution efficiency inside the draft tube as compared to the central aeration. The mathematical approaches and the numerical methods employed here can be used to design and optimize the aeration process in these systems