Theoretical And Experimental Study On Hydrodynamic Performances Of Vertical-Axis Tidal Turbine

Vertical-axis tidal turbines are one type of extensively tested and studied energy conversion systems for marine currents application. They can work smoothly even in shallow water and at low velocity of flow. And they do not need any special yaw mechanism to be oriented to the flow direction, making them simple in structure and reliable in working. Vertical-axis tidal turbines usually can obtain considerable power coefficient and be self-start by providing appropriate variable-pitch blades. So more and more attention is now paid on the design of new kind of variable-pitch mechanism and the improvement of hydrodynamics calculation method for this kind of turbine which are just the principal objects of this thesis.One aim of this work is to test a spring controlled passive variable-pitch mechanism. So at first analysis for the hydrodynamic influence of TSR and pitch angle is carried out by improving the theoretical model of performances, the working principle of the variable-pitch mechanism is summarized also. Then various concepts of variable-pitch designs are evaluated in detail. And the spring controlled passive variable-pitch mechanism is designed; a prototype constructed and model experiments done. Results have demonstrated that the turbine can self-start and the power coefficient is enhanced. At last the hydrodynamic performances of the spring controlled variable-pitch turbine are analyzed with the influence parameters such as spring stiffness and blade solidity. All of these results can be used as references for further design and validation for the mathematical calculation model.The second aim is to improve the performance calculation model for the vertical-axis tidal turbines, especially for passive variable-pitch ones. As result two theoretical models are presented in this thesis. One is the classic double-disk multi-streamtube model based on momentum theory. This method has been applied to passive variable-pitch turbine by combining blade dynamic analysis. The calculation is improved by considering streamtube expansion, dynamic stall...