High wind speeds associated with Low-Level Jet (LLJ) make wind resources more favorable for wind energy production. However, the aerodynamic loads of large-scale horizontal axis wind turbine (HAWT) rotor under different LLJ inflow conditions have not been thoroughly studied. To gain insight into the aerodynamic loads of rotor under LLJ inflow conditions with different LLJ intensities, a method to establish an engineering LLJ inflow model was proposed according to the plane wall jet theory and Von Karman spectra model with user-defined scaling. The parameters in the engineering LLJ inflow model were determined by comparing the wind speed distribution obtained from the GP_LLJ spectral model, which was summarized from field measurements in the real atmosphere. The LLJ fluctuating wind fields with different intensities generated by the engineering LLJ inflow model were used as the inflow conditions of Fatigue, Aerodynamics, Structures, and Turbulence (FAST) open source code to calculate and analyze the aerodynamic loads of the HAWT. It was found that the engineering LLJ inflow model can be used to establish the LLJ inflow condition of HAWT. When the LLJ height is located at the hub height and LLJ intensity increases from 8 to 16 m/s, the RMS rotor unbalanced aerodynamic load coefficients, including ones of lateral force, longitudinal force, tilt moment and yaw moment are increased by 2.2, 2.13, 1.02 and 0.95 times, respectively.
ARTICLE HISTORY
The airfoil plays an important role in improving the performance of wind turbines. However, there is less research dedicated to the airfoils for Vertical Axis Wind Turbines (VAWTs) compared to the research on Horizontal Axis Wind Turbines (HAWTs). With the objective of maximizing the aerodynamic performance of the airfoil by optimizing its geometrical parameters and by considering the law of motion of VAWTs, a new airfoil, designated the LUT airfoil (Lanzhou University of Technology), was designed for lift-driven VAWTs by employing the sequential quadratic programming optimization method. Afterwards, the pressure on the surface of the airfoil and the flow velocity were measured in steady conditions by employing wind tunnel experiments and particle image velocimetry technology. Then, the distribution of the pressure coefficient and aerodynamic loads were analyzed for the LUT airfoil under free transition. The results show that the LUT airfoil has a moderate thickness (20.77%) and moderate camber (1.11%). Moreover, compared to the airfoils commonly used for VAWTs, the LUT airfoil, with a wide drag bucket and gentle stall performance, achieves a higher maximum lift coefficient and lift–drag ratios at the Reynolds numbers 3 × 105 and 5 × 105.
In this paper, the effect of the three typical tip vanes on the loading of an H-VAWT is investigated by employing the three-dimensional unsteady numerical simulation method. The results show that the both transient tangential force coefficient (CT) and normal force coefficient (Cn) have obvious change when the winglet and the V type vane is used at the blade's tip, respectively. However, in three tip vanes, the CT average value is the lowest and the CT fluctuation characteristic is the highest when the winglet is used. Although the winglet and V type vane contribute to change the transient CT and Cn, the normal force is increased too, it results in increasing fatigue loading and decreasing lifetime for H-VAWT. By comparison, the effect of the plate vane on the loading is weaker. Additionally, the winglet is advantage to improve power coefficient in the low tip speed ratio.
One of the important challenges for Vertical Axis Wind Turbine (VAWT) is to fully understand its dynamic characteristics in different operating conditions. Meanwhile, it is necessary to seek a fast and accurate method to evaluate the dynamic characteristic of VAWT. In this study, we improve the LB model by considering the operating principle of VAWT to study the dynamic characteristics of the dedicated and commonly used VAWT airfoils in different operating conditions. The results show that the improved LB model is suitable for simulating the dynamic characteristic of VAWT with a thick airfoil. Although the asymmetric airfoil shows the higher lift coefficient, their dynamic characteristic appears huge fluctuation as the increases of tip speed ratio. Moreover, at a low tip speed ratio, the advantages of the asymmetric airfoil are not obvious. While the dynamic characteristic of the symmetric airfoil is relatively stable with the variation of tip speed ratio.
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