Predicting hydrokinetic turbine power generation is difficult due to complex geometry, highly turbulent conditions, and difficulty capturing the transient interface existing between air and water.A threedimensional finite volume solver was used to capture the effects resulting from free surface interaction with the aid of a Volume of Fluid(VOF) multiphase solver.Depths from free surface level to blade tip with corresponding Froude numbers of 0.71, 0.92, 1.04, and 1.31 were modelled specifically to capture the transition from subcritical to supercritical flow conditions.A sharp decrease in performance was observed at the critical Froude number (Fr=1.0).Results at subcritical conditions showed acceptable agreement with previously published single phase results where the turbine is assumed to be operating in aninfinite medium.At subcritical conditions, the propeller-based turbine studied was compared to numerical and experimental results obtained for a traditional marine current turbine (MCT).As the flow became critical, a 32.2% decrease in the power coefficient was predicted and significant wake-free surface interaction was observed.
Articles you may be interested inA coupled hydro-structural design optimization for hydrokinetic turbines Numerical investigation and evaluation of optimum hydrodynamic performance of a horizontal axis hydrokinetic turbine Computational Fluid Dynamics, a crucial tool in exploring designs of hydraulic machinery, is used to evaluate the design of a non-uniform Archimedean spiral rotor. A transient simulation method is implemented using a frame of reference change between time-steps to capture the flow field correctly. The boundary conditions for this method are discussed and are validated with previously published experimental data using a flat plate propeller turbine. A spectral and temporal convergence study for the non-uniform Archimedean spiral rotor is performed to verify solution independence of mesh and time-step selection. Performance characteristics of the rotor are provided over a wide range of volumetric flow rates and rotation rates. The best hydraulic efficiency point is determined to be 72% for the presented rotor design and is compared with the performance of similar micro-hydro turbines. V C 2014 AIP Publishing LLC.
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