Research On Flow Field Simulation And Airfoil Design Method For Vertical Axis Wind Turbines Operating At Variable Tip Speed Ratios

For the purpose of establishing sustainable city, wind energy development in cities has become a new way in wind energy utilization. With the merits of structure, no yaw system, easy maintance and establishment, H type vertical axis wind turbine is more suitable for urban wind power generation than horizontal axis wind turbine. Nevertheless, there is lack of research on the physics of vertical axis wind turbine unsteady flow field and airfoil design, which is not helpful to the improvement of turbine aerodynamic performance and application of H type vertical axis wind turbine. Thus, all these issues have been studied systematically in this dissertation. To ensure the test result can be applied for guiding the aerodynamic design, theory of similitude and dimensional analysis method have been applied for deducing the design rule of experimental rotor. An experimental platform has been fabricated and the aerodynamic data measuring method were illustrated, laying the foundations of relevant experimental test.An experimental H type machine has been selected as study object, the influence of variable turbulence models, mesh types, y plus values and time step sizes on simulational results by URANS methods have been investigated. Values of major parameters of URANS method has been confirmed on the basis of computational accuracy and efficiency.The flow field under variable tip speed ratios has been simulated by URANS method. It has been found that, the main feature of rotor flow field is frequent balde dynamic vortexes generating and shedding at low tip speed ratio while periodic balde wakes generating and diffusing at high tip speed ratio. Both of the two kinds of features have negative influences on rotor torque coefficient and power coefficient. The orientation of airfoil design should be avoiding or delaying the flow separation and vortex shedding at lower tip speed ratio, reducing the blade wakes and its spreading range.The concept of averaging effective wind energy utilization coefficient was presented, which can be used for evaluating aerodynamic performance of H type turbine under variable tip speed ratios. The aerodynamic computational model for H type machine under variable tip speed ratios was studied, which resolving the problem that high accuracy and time consuming when applying CFD method in airfoil design.The airfoil design method of H type machine under variable tip speed ratios was studied, and a new airfoil OPTFoil2014 has been designed. Another airfoil OPTFoil2011 was designed based upon complex method, using Xfoil combing withViterna model sloving airfoil aerodynamic performance. The aerodynamic performance of rotors with airfoil NACA0015, DU 06-W-200, OPTFoil2011 and OPTFoil2014, was compared by numerical simulation at the wind speed of 8 m/s. It has been found that, comparing to with traditional used airfoil NACA0015, the improving rate of rotor aerodynamic performance by OPTFoil2014 was the highest. The averaging effective wind energy utilization coefficient increased by 6.78%. The aerodynamic performance of rotors with airfoil NACA0015, DU 06-W-200, OPTFoil2011 and OPTFoil2014, were tested in the wind tunnel at wind speed from 6m/s to 10m/s. It has been found that averaging effective wind energy utilization coefficients of all airfoils rised with the increasing of wind speed, but the growth rates became smaller with the rising wind speed. Comparing to traditional used airfoil NACA0015, the highest improving rate of the averaging effective wind energy utilization coefficient came from OPTFoil2014, the maximum value 7.86% obtaining at 6 m/s and minimum value 4.89% acquiring at 10 m/s.It can be concluded from the numerical simulation and experimental test, comparing with the design method that using single airfoil performance as design object, the airfoil design method of H type VAWT airfoil under variable tip speed ratios that using the averaging effective wind energy utilization coefficient as design object, takes into account rotor aerodynamic performance at different tip speed ratios, the airfoil design by this method makes the H type machine possessing better aerodynamic performance under variable tip speed ratios.