Three different horizontal axis wind turbine (HAWT) blade geometries with the same diameter of 0.72 m using the same NACA4418 airfoil profile have been investigated both experimentally and numerically. The first is an optimum (OPT) blade shape, obtained using improved blade element momentum (BEM) theory. A detailed description of the blade geometry is also given. The second is an untapered and optimum twist (UOT) blade with the same twist distributions as the OPT blade. The third blade is untapered and untwisted (UUT). Wind tunnel experiments were used to measure the power coefficients of these blades, and the results indicate that both the OPT and UOT blades perform with the same maximum power coefficient, C_p = 0.428, but it is located at different tip speed ratio, λ = 4.92 for the OPT blade and λ = 4.32 for the UOT blade. The UUT blade has a maximum power coefficient of C_p = 0.210 at λ = 3.86. After the tests, numerical simulations were performed using a full three-dimensional computational fluid dynamics (CFD) method using the k-ω SST turbulence model. It has been found that CFD predictions reproduce the most accurate model power coefficients. The good agreement between the measured and computed power coefficients of the three models strongly suggest that accurate predictions of HAWT blade performance at full-scale conditions are also possible using the CFD method.

In designing a horizontal-axis wind turbine (HAWT) blade, system integration between the blade design and the performance test of the generator is important. This study shows the aerodynamic design of a HAWT blade operating with an axial-flux permanent magnet (AFPM) generator. An experimental platform was built to measure the performance curves of the AFPM generator for the purpose of designing the turbine blade. An in-house simulation code was developed based on the blade element momentum (BEM) theory and was used to lay out the geometric shape of the turbine blade, including the pitch angle and chord length at each section. This simulation code was combined with the two-dimensional (2D) airfoil data for predicting the aerodynamic performance of the designed blades. In addition, wind tunnel experiments were performed to verify the simulation results for the various operating conditions. By varying the rotational speeds at four wind speeds, the experimental and simulation results for the mechanical torques and powers presented good agreement. The mechanical power of the system, which maximizes at the best operating region, provided significant information for designing the HAWT blade.

This paper experimentally studies the basic characteristics of an isolated two-dimensional synthetic jet actuator (SJA) and two resonance frequencies found at 40Hz and 160Hz, which are respectively corresponding to the resonance of diaphragm and resonance of cavity of SJA, Data indicate that the former is independent of various excitation waveforms, excitation voltages and exit area of the SJA orifice. The latter is only associated with the exit area of the orifice. In addition, the dimensionless stroke length (Ld) is proportional to the Reynolds number of the exit velocity for the diaphragm resonance at various excitation voltages. As for the cavity resonance, the important result is that the dimensionless stroke length is proportional to Re3/2 for all four different excitation voltages and the effective neck length (l’) doesn’t keep constant with the varying exit area of orifice. That is, the l’ increases linearly with the increasing A2/3. Regarding the relationship among the maximum ejection velocity (Ūe, max), mean ejection velocity (Ū) and the resonance frequency of cavity (fc) at various voltages of excitation, both Ūe, max and Ū are inversely proportional to the fc3/2 in this study. The current experimental results are expected to be useful for designing a synthetic jet actuator for real applications