Design, Modeling, and Prototyping of a Hydrokinetic Turbine Unit for River Application

Abstract Marine hydrokinetic technology is a fast growing field that aims to capture energy from flowing water. Micro-hydrokinetic technologies are a subset of marine hydrokinetic systems, operating at much smaller scales generally considered less than 100 kW of power production. Small-scale production is applicable for disaster relief and for military application. A propeller-type hydrokinetic design with a high solidity was designed to meet the needs of the Marine Corps in providing 500 Watts of continuous power while also providing portability. The finite volume method was used to solve the Reynolds-Averaged Navier Stokes equations with the k-ω Shear Stress Transport turbulence model. The boundary layer was resolved using wall functions to efficiently and effectively predict power production. The Volume of Fluid multiphase model along with Open Channel boundary conditions and a Numerical Beach was implanted to capture free surface effects. It was determined that at a Froude number of 1.0 the mechanical power drops by approximately 33%. The drop in power production was due to enhanced wake-free surface interaction as the blade tip approached the free surface. Based on turbine-diffuser characterization, rapid-computational fluid dynamics simulations, and free surface, multiphase simulations, a prototype was designed and developed to produce 250 Watts of power. The final design utilized specific flow conditions corresponding to the greatest percentage of potential installation sites where the unit could be deployed. Numerical predictions were produced for the final hydrokinetic turbine system, with a peak power coefficient value of 0.51 at a tip speed ratio of 2.5. Experimental tests were conducted at the Circulating Water Channel (CWC) at the Naval Surface Warfare Center. The turbine operated in various flows ranging from 1.0 m/s to 1.7 m/s. The system produced 388.0 W of power at 1.7 m/s of flow, yielding a peak efficiency of 0.36 at a corresponding tip speed ratio of 2.5. The power observed from experiments showed positive agreement, with relative error less than approximately 3%, with that of the numerical predictions. The positive agreement between the numerical and experimental results validates the numerical methods applied to the design, modeling, and optimization of the turbine blades.