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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 OPEN ACCESSEnergies 2013, 6 2785 suggest that accurate predictions of HAWT blade performance at full-scale conditions are also possible using the CFD method.

A development procedure for a low-cost attitude and heading reference system (AHRS) with a self-developed three-axis rotating platform has been proposed. The AHRS consists of one 3-axis accelerometer, three single-axis gyroscopes, and one 3-axis digital compass. Both the accelerometer and gyroscope triads are based on micro electro-mechanical system (MEMS) technology, and the digital compass is based on anisotropic-magnetoresistive (AMR) technology. The calibrations for each sensor triad are readily accomplished by using the scalar calibration and the least squares methods. The platform is suitable for the calibration and validation of the low-cost AHRS and it is affordable for most laboratories. With the calibrated parameters and data fusion algorithm for the orientation estimation, the self-developed AHRS demonstrates the capabilities of compensating for the sensor errors and outputting the estimated orientation in real-time. The validation results show that the estimated orientations of the developed AHRS are within the acceptable region. This verifies the practicability of the proposed development procedure.

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This paper explores the control of wall-separated flow on a NACA 63 3 -018 airfoil and a circular cylinder by using the internal acoustic excitation technique. Experimental study of the characteristics of the flow under internally emanating acoustic waves is performed in an open-type, suction wind tunnel. Tests are carried out at the Reynolds number ranging from 6.3 x 10 3 to 5.0 x 10 5 based on the relevant characteristic lengths, the airfoil chord, and the cylinder diameter. The control effectiveness is verified by the measurements of parameters such as the excitation frequency, the excitation level, and the forcing location. Data indicate that the excitation frequency and the forcing location are the key parameters for controlling the separated flow, and the forcing level is the least-effective parameter for the study. As long as the emanating acoustics is "locked in" to the separated shear-layer instability frequency and forcing is applied at the separation point, the separated flow is controlled most effectively. Moreover, the b'ft is increased and the drag reduced dramatically. Nomenclaturecircular cylinder f e = excitation frequency f s = vortex shedding frequency f t = shear layer instability frequency P = static pressure P t -total pressure p tao = total pressure in freestream P^ = static pressure in freestream Re c = Reynolds number based on chord, Re c = U^ C/v Re D = Reynolds number based on diameter, Re D -U^D/v St = Strouhal number, (/,<:/#«,) or (f.D/U^) U^ = freestream velocity X = coordinate along the freestream direction Y = coordinate normal to the freestream direction p = fluid density v = kinematic viscosity a = sound emission angle of the circular cylinder 0 = polar coordinate in the azimuthal direction