Large eddy simulations of ventilated micro hydrokinetic turbine at design and off-design operating conditions

Multiphase large eddy simulations (LES) were conducted for ventilated micro hydrokinetic turbine operating at design and off-design operational conditions. The simulations were performed with and without aeration at the design tip-speed ratio of 1.86 and at off-design tip-speed ratios of 1.2 and 2.7. The spatial and temporal characteristics of oxygen dissolution into the water were examined. The nominal value of power generation for the tip-speed ratio of 1.2 decreased slightly with aeration, while it increased slightly at the tip-speed ratio of 1.86 and 2.7. Slight increase in thrust was also observed for each case. The standard deviation of both power and thrust coefficient were increased more than 47% with air injection at the tip-speed ratio of 1.2, while the standard deviation of the thrust coefficient decreases by approximately 18% at the tip-speed ratio of 1.86 and 2.7. The suppression of small eddies and the early dissipation of tip vortices in multiphase simulations in the cases of the tip-speed ratio of 1.86 and 2.7 can be related to more stable turbine operation with aeration. It is demonstrated here that micro hydrokinetic turbines can be used effectively for aeration purposes at wide range of operating conditions.