This thesis proposes equations extending the Free Surface Actuator Disc Theory to yield drag forces and interference factors from a series of two porous discs in open channel flows. The new model includes blockage ratio and Froude number as independent variables, which are inferred in advance to yield a single solution in the prescribed domain. The theoretical extension is integrated with the Blade Element Theory in a Double Multiple Streamtube model (DMS) to predict axial loads and the performance of confined Darrieus turbines. The turbine thrust force influences the flow approaching the rotor. Hence, a momentum method is applied to solve the hydraulic transition in the channel, achieving the unknown inflow factor from the undisturbed flow imposed downstream. The upstream blockage ratio and Froude number are thus updated iteratively to adapt the DMS to subcritical applications. The DMS is corrected further to account for the energy losses due to mechanical struts and turbine shaft, flow curvature, turbine depth, and streamtube expansion. Sub-models from the literature are partly corrected to comply with the extended actuator disc model. The turbine model is validated with experimental data of a high-solidity cross-flow hydrokinetic turbine that was previously tested at increasing rotor speeds. Turbine arrays are investigated by integrating the previous turbine model with wake sub-models to predict the plant layout maximizing the array power. An assessment of multi-row plants shows that the array power improves with closely spaced turbines. In addition, highly spaced arrays allow a partial recovery of the available power to be exploited upstream by a new turbine array. The highest array power is predicted by simulations on different array layouts considering constant array blockage ratio and rotor solidity. Finally, assuming a long ideal channel, the deviation in the inflow depth is speculated to become asymptotic after many arrays, implying almost identical power conversion upstream.

Globally the amount of electricity produced each year is increasing significantly. Between 1980 and 2010 the average increase was 407 billion kWh per year. To be able to meet this increasing electricity demand, without burdening the environment in a too large extent, the research and development of renewable energy production techniques is of great importance. In the light of this we wanted to dedicate our master thesis to help SubseaTechnology Scandinavia AB with the development of a vertical axis tidal current turbine. The project set out to do the initial design proposal of a 2 x 4 meter H-shaped Darrieus turbine by applying the Double Multiple Streamtube model. The optimization process was performed with the aid of MATLAB for four different foils. The study included two symmetrical foils; NACA 0012 and S-1046 together with two asymmetrical foils; S-1210 and E216. The parameters studied were the number of blades, chord length, tip speed ratio, fixed pitch and the operational range. In the project, effects such as blade to wake interaction, torque fluctuations etc. were also considered. From the simulations the two bladed turbine fitted with the S-1046 hydrofoil showed the highest performance but was struggling with an unfavorable oscillating torque. In the light of this the three bladed turbine fitted with the S-1046 hydrofoil with a chord of 0.13 m and an optimal tip speed ratio of 3.2 was determined. From the simulations the power coefficient reached 53.47 % for this case. This configuration also showed good performance in a relatively wide range of both tip speed ratios and free stream velocities. The model does not include several effects causing losses and the power coefficients calculated in this model are to be used as a comparison between the different turbine configurations and not as absolute values of performance. The simulations showed good potential for the use of asymmetrical foils in vertical axis turbines. The performance was evaluated for the upstream half of the turbine where the E216 foil exceeded the symmetrical foils in the range of ten percentage points.

No description available.