Diffuser augmented hydrokinetic turbines and their application in rivers

Abstract

Hydrokinetic turbines are suitable for exploiting unused potential for electrical energy generation in rivers, since they can be used comparatively simple also in sensitive areas. When applied in rivers, the rotor diameter and thus also the power of such a turbine is often limited by a low flow depth. Therefore, it is advisable to equip the rotor with a diffuser at such locations. A large diffuser opening to the sides can increase the projected area of the machine and thus the power. In order to determine the exact power for such a diffuser augmented hydrokinetic turbine at a potential site an advanced turbine model for 2d shallow water simulations is developed in this work. This requires a deep understanding of this particular turbine type, which is obtained by detailed numerical investigations of several different diffuser geometries. Also site effects, such as the blockage effect of kinetic turbines in narrow channels and sheared flow effects, are investigated in detail by means of numerical 3d flow simulations. All findings from these studies are included in the development of the advanced turbine model. Regarding the model implementation in the 2d shallow water solver also the blockage effect in the 2d model has to be considered. Among other things, this effect causes the high sensitivity of the model to the dimensioning of the turbine cell. The final turbine model is applied to simulate turbines in different rectangular channels and at a potential site in Montreal, Canada. The results are compared with results of corresponding 3d simulations to successfully verify the model. Finally, the model is applied to evaluate the arrangement of five diffuser augmented hydrokinetic turbines. A total hydraulic power of the turbine park of around 1.8 MW is determined. This could supply around 635 Canadian households with electricity.