Aerodynamic Design And Performance Analysis Of Lobed Ejector In Wind Turbines

Energy is the foundation of human survival and social progress. Wind energy can be regarded as one of the important sustainable energy. In the current, the wind energy used by commercial fans is only high speed wind energy. However, the wind speed changes in the range of 2-6 m/s in most regions of China. It attracts much attention on how to design a kind of low speed wind turbine with higher wind energy utilization efficiency.This paper developed the design of low speed wind turbine consisting of lobed ejector and single stage turbine. The parameterized design of 3D modeling had been used to discuss the structural optimization method of lobed ejector. Through the numerical simulation, the velocity distribution of the air flow inside and outside the bypass and the interaction between two kinds of vortices in the flow field were analyzed. Finally, the multivariate nonlinear regression analysis method in optimum design for the lobed ejector was used to achieve the highest wind energy utilization efficiency.The simulation result showed that there were two kinds of vortices in the flow field of a lobed ejector, namely streamwise vortices caused by bypass airflow radial pressure gradient and normal vortices caused by K-H wave generated by the flow velocity difference inside and outside the bypass. In the flow field near the trailing edge of the lobes, two kinds of vortices expanded the scope and the maximum vorticity reduced. Then, the streamwise vortices deflected, the high vorticity dropped and branched near the outlet of bypass in the plane of Z=0.3m. Due to the entrainment and dissipation of streamvise vortices, normal vortices broke into two partial normal vortices called "Peak region" and "Trough region" in the downstream of the lobed ejector. The migration of the Trough region lead to the interaction between Trough regions induced by adjacent lobes. The two sides of the Trough region merged into the Peak region. Then the Peak region blend with the far field airflow completely in the plane of Z=5.0m. The interaction of streamwise and normal vortices promoted the mixing process. By measuring the pressure of different relative blade height in the outlet of the rotor, it can be proved that the lobed ejector strengthen the mixing process of the air flow inside and outside the bypass, reduced the outlet pressure of the rotor, decrease of the enthalpy of the air flow inside the bypass, so that the working capacity of the air flow inside the bypass is improved, which enhances the wind energy utilization efficiency of the low speed wind turbine.Through the optimization analysis, this paper finally made the decision of the optimized structure with highest wind energy utilization efficiency. After the analysis on the aerodynamics characteristics of the optimized structure on the condition of deviating from the design point, the excellent characteristics of the low speed wind turbine were validated. The results showed that the torque of the rotor is proportional to the square of the inlet velocity, and the power of the wind turbine is proportional to the cube of the inlet velocity at optimal tip speed ratio. In the off-design conditions of 15%, wind energy utilization efficiency reduces only 3.3%.