Design And Research On The Blade Of Horizontal Axis Impeller For Tidal Current Power Capture

As the fossil energy is drying up day by day, and the demand of industry and life for energy is greatly increasing, the exploitation and utilization of alternative energy is already in the extremely urgency. Tidal current energy, which is well recognized by the world for its clean, renewable, higher density, and abundant storage advantages, has been actively developed. The blade is the key part of horizontal axis tidal current energy conversion devices for the conversion from the tidal current energy into mechanical energy. Its performance directly determines the capture efficiency of the whole tidal current energy generator. Therefore, in order to optimize our country’s energy consumption structure, relieve the coastal regions of energy pressure, and even improve our living environment, it is of far-reaching significance to study deeply the hydrodynamic theory and model of the blade, optimize the design of the profile of the blade, and capture the tidal energy and then convert it into electricity efficiently.The design of the current horizontal axis blades for tidal current energy capture commonly refers to the design of the blades of aerogenerator, and the blade profiles adopted are mostly dedicated profiles for aerogenerator. Aiming at this problem, the dynamic characteristics of these mainly adopted blade profiles were theoretically analyzed and numerically simulated in the thesis, and it was found that under the action of fluids with different Reynolds numbers, the dynamic characteristics of the blades with different profiles differed greatly from each other. The Reynolds number of the flow field of the aerogenerator blades is much greater than that of the tidal current energy capture blades, the lift-to-drag ratio of the tidal current energy capture blades counts only 40% of that of the aerogenerator blades because of much smaller radius and at much lower current speed, while the density of the tidal current is about 794 times of that of the wind, and the kinetic energy per unit area carried by the tidal current counts about 6.35 times of that carried by the wind. Therefore, in the design of the tidal current energy capture blades, the impact action of the tidal current should be fully taken into account. Otherwise, lower energy capture efficiency of the blades would be resulted.On the basis of summing up the various current design theories and methods, the flow field of and the forces acted on the horizontal axis tidal current energy capture blades were analyzed in the thesis, and the hydrodynamic models of the blade under the actions of differential pressure lift force and the tidal current impact force were established, respectively, according to the theory of blade element momentum and Bernoulli principle. Considering the torques and axial forces produced by both of the actions and introducing in the coefficient of impact energy capture, the general hydrodynamic model of the blade was obtained. When the coefficient of impact energy capture is zero or the impact force is much smaller than the differential pressure lift force, this general model will retrogress to Glanert design model.Almost all of the profiles of the current tidal current energy capture blades have the features that their curvature is small, and the primary curvature is at the front of the blades, but it is almost straight at the rear. Therefore, they are not appropriate for capturing the impact energy, and their auto-start capability is poor. To overcome these shortcomings, the structure of the blade profile was optimized based on the hydrodynamic model established in the thesis, by taking the maximum power capture coefficient as the objective, the lift force coefficient without obvious decrease and the drag force coefficient without obvious increase as constraints, and the profile Naca6412 as the prototype. By means of FLUENT software tool, the performance of the optimized profile was numerically simulated, and the results show that its dynamic characteristics meet well the design goal, which also indicates that the increase of the curvature at the rear part of the blade favours the capture of the impact energy.Based on the above study, the optimal cord length and twist angle of the ideal blade was designed by means of the Matlab software tool, the space coordinates of 11 cross sections of the blade were calculated, the 3D model of the blade was build up by means of the UG software tool and the corresponding NC program was generated through the NC module, and a model of the impeller with a diameter of 0.5m was manufactured and tested with the water tank and test facilities in our laboratory. Test results show that the blade designed optimally with the consideration of the combined action of the differential pressure lift force and the impact force has a better auto-start characteristic and higher tidal current energy capture efficiency. Thereby, the validity and effectiveness of the hydrodynamic model established and the optimal blade design method proposed in the thesis are verified.