Numerical Simulation On Fluid Dynamic Performance Of H-shaped Vertical Axis Turbine And Duct

H-shaped turbine is the common and key equipment in Vertical axis wind turbine generator system or (marine) tidal streams turbine generator system, with the characteristics of the main axis perpendicular to the flow direction, the blade parallel to the main axis. So the flow direction has no influence with turbine rotations. The structure of blade is simple, which is easy to implement angle-changed control and large-scale production. Therefore, vertical axis turbines are highly concerned in the electric generation technology from wind energy and tide energy in recent years. Due to the fact that it is unsteady and unsymmetrical in flow field, trailing vortex and load on the blade during the working process of H-shaped turbine, besides, fluid dynamic disturbing effect is complex, many basic mechanic problems in turbine fluid dynamic performance design have not been solved as yet. Consequently, it is important theoretical and practical significance in accurately understanding and improving design capacity of H-shaped turbine, in studying fluid dynamic theory and numerical simulation methods, exploring flow characteristics, fluid dynamics mechanism and performance of H-shaped turbine.The methods of predicting hydrodynamic performance for H-shaped turbine are usually stream tube method and vortex method. Stream tube method is simple and quick in analyzing the overall performance, however, it is difficult to predict blade instantaneous load performance. Vortex method can calculate the instantaneous load and simulate vortex interference, however, when the blade moves in the range for angles of attack and flow begins to distribute, the calculation is not accurate, while viscous CFD method overcomes shortcomings mentioned above. Based on viscous CFD method and Fluent software, the numerical simulation method of H-shaped turbine flow field, fluid dynamic loads and performance of blades, the turbine and the duct are studied in this thesis.Firstly, numerical simulation method of flow field for H-shaped turbine are studied. Aimed at the section of blade, numerical simulation of steady and unsteady flow around the typical symmetry aerofoil are studied, and relevant calculation conditions and treatments in viscous CFD theory are discussed, besides, based on the characteristics of sliding mesh and dynamic mesh, the UDF controlled sliding mesh (UDF-SM) is put forward. Two numerical examples of Strickland wind turbine and Kurushima Strait tidal stream turbine demonstrate that the sliding mesh model can forecast accurately instantaneous load on blade, especially, it is more accurate to calculate performance in low speed ratio. Performance simulation of cycloidal hydro-turbine indicates UDF-SM model can calculate the power characters of variable pitch-angle H-shaped turbine, compared to dynamic mesh model, it can decrease mesh number on the premise that the mesh quality is guaranteed, therefore, it can save the calculating time.Secondly, fluid dynamics of the blade moving in viscous flow is studied. Balanced force equation and balanced torque equation of blade are formulated into UDF program, and then the working process of H-shaped turbine with inertial force system is simulated, giving the variety law of blade and the power efficiency characteristics of turbine. The comparison of numerical results and experimental results shows that this method can effectively predict the blades' motion and power efficiency characteristic of turbine.In addition, the general fluid dynamic performance of rotor are studied. The amendment formulas on the power efficiency of variable-pitch H-shaped turbine are presented, by considering the blade moment's work on the shaft in energy conversion. The calculation results show that the influence of amendment on power efficiency is small in the low speed ratio while it is large in the high-speed ratio. The power efficiency amendment provide a method for calculating the performance of the rotor more accurately.At last, work on the method to enhance the performance of H-shaped rotor. Duct design method is put forward that suitable for reciprocating flow, and the design concept of expansion door is presented. In addition to calculate the characteristics of duct in flow field individually, the flow fields are simulated about the duct with fixed blade wind turbine, with cycloidal hydro-turbine and spring-controlled passive variable-pitch turbine respectively. The dynamic interference between duct and rotor is discussed. Numerical and experimental results show that the duct can stabilize the flow in rotor downstream disk, expansion door can enlarge the flux in duct evidently. The influence on power efficiency and fluid dynamic characteristics of blade by duct parameters such as the moulded line, shrinking ratio, gap between duct and turbine will change along with the rotor's type. The duct with expansion-door is better than the one without it. In experiment, the peak of power efficiency of spring-controlled variable-pitch turbine is enhanced 47.8% by duct with expansion door, meanwhile the speed ratio range for effective operation of turbine is extended.The research work in the thesis provide a numerical simulation method to viscous flow problems for various H-shaped turbine. It is valuable in studying fluid dynamic mechanics, optimizing blade performance and design and improving turbine efficiency of H-shaped turbine, being significance in theory and engineering application.