Fault diagnosis is essentially a kind of pattern recognition. The measured signal samples usually distribute on nonlinear low-dimensional manifolds embedded in the high-dimensional signal space, so how to implement feature extraction, dimensionality reduction and improve recognition performance is a crucial task. In this paper a novel machinery fault diagnosis approach based on a statistical locally linear embedding (S-LLE) algorithm which is an extension of LLE by exploiting the fault class label information is proposed. The fault diagnosis approach first extracts the intrinsic manifold features from the high-dimensional feature vectors which are obtained from vibration signals that feature extraction by time-domain, frequency-domain and empirical mode decomposition (EMD), and then translates the complex mode space into a salient low-dimensional feature space by the manifold learning algorithm S-LLE, which outperforms other feature reduction methods such as PCA, LDA and LLE. Finally in the feature reduction space pattern classification and fault diagnosis by classifier are carried out easily and rapidly. Rolling bearing fault signals are used to validate the proposed fault diagnosis approach. The results indicate that the proposed approach obviously improves the classification performance of fault pattern recognition and outperforms the other traditional approaches.

Making good use of vertical axis wind turbines (VAWTs) is an attractive and potential way to deal with the energy and environmental issues due to the unique superiorities of it. Computational Fluid Dynamics (CFD) technology is a useful tool for the design process of VAWTs. Various turbulence models have been developed and available for turbulent flow simulations. Currently, there have been few researchers studying on meshing strategies and turbulence model selections of VAWT simulations. In this paper, 2D unsteady models under 4 meshing strategies and 6 turbulence models were established and simulated to investigate the effect of the above two aspects on numerical simulations of VAWTs. The numerical results were compared with the experimental data of Oler et al. (“Dynamic stall regulation of the Darrieus Turbine,” SAND Report No. 83–7029, Sandia National Laboratories, Albuquerque, 1983, pp. 67–96) and the analytical solution of Deglaire et al. (Eur. J. Mech., B: Fluids 28(4), 506–520 (2009)). The results reveal that a mesh of 213 656 grids is sufficient to meet the requirements of grid independence with the help of boundary layer and size function techniques. Besides, the realizable k-ε model enables the closest CFD simulation of the experimental data and shows better prediction performance than the analytical model of Deglaire et al. and other turbulence models.

This paper presents a new variable pitch (VP) approach to increase the peak power coefficient of the straight-bladed vertical-axis wind turbine (VAWT), by widening the azimuthal angle band of the blade with the highest aerodynamic torque, instead of increasing the highest torque. The new VP-approach provides a curve of pitch angle designed for the blade operating at the rated tip speed ratio (TSR) corresponding to the peak power coefficient of the fixed pitch (FP)-VAWT. The effects of the new approach are exploited by using the double multiple stream tubes (DMST) model and Prandtl’s mathematics to evaluate the blade tip loss. The research describes the effects from six aspects, including the lift, drag, angle of attack (AoA), resultant velocity, torque, and power output, through a comparison between VP-VAWTs and FP-VAWTs working at four TSRs: 4, 4.5, 5, and 5.5. Compared with the FP-blade, the VP-blade has a wider azimuthal zone with the maximum AoA, lift, drag, and torque in the upwind half-cycle, and yields the two new larger maximum values in the downwind half-cycle. The power distribution in the swept area of the turbine changes from an arched shape of the FP-VAWT into the rectangular shape of the VP-VAWT. The new VP-approach markedly widens the highest-performance zone of the blade in a revolution, and ultimately achieves an 18.9% growth of the peak power coefficient of the VAWT at the optimum TSR. Besides achieving this growth, the new pitching method will enhance the performance at TSRs that are higher than current optimal values, and an increase of torque is also generated.

Variable-pitch (VP) technology is an effective approach to upgrade the aerodynamics of the blade of an H-type vertical-axis wind turbine (VAWT). At present, most of the research efforts are focused on the performance improvement of the azimuth angle owing to the large angle of attack (AoA). On the blade circular path of an H-type VAWT, there are two azimuth positions where torques are negative, and the performance is the poorest. The vicinity zones of the two azimuths also have low performance and greatly weaken the overall productivity of VAWT. In this paper, we propose a new technology that, unlike the traditional VP-technology, focuses mainly on the aerodynamics improvement of the azimuth position with small AoA. The purpose of this novel approach is to widen the band of azimuth positions with high performance and eventually enhance the power efficiency of the overall VAWT. The performance of the new VP-VAWT is predicted using the Double Multiple Streamtubes model and Prandtl's mathematics to evaluate the blade tip loss. Compared with the fixed-pitch (FP) blade, the VP-blade has a wider zone of the max AoA and tangential force in the upwind half-circle and yields the two new larger max values in the downwind half-circle. The new VP-strategy considerably narrows the two low-torque zones near the 0° and 180° azimuths and markedly widens the high-torque azimuth zone; the torque distribution appears in a trapezoidal shape in the upwind region and an M-like shape in the downwind region. The power distribution in the swept area of turbine changes from an arched shape of the FP-VAWT into a rectangular shape of the VP-VAWT. At last, an 18.9% growth in power efficiency is achieved. All of the above results confirm that the new VP-technology can effectively improve VAWT performance and also widens the highest performance tip speed ratio zone which makes the turbines capable of running with high efficiency in wider zones.

A simplified free vortex wake (FVW) model called the vortex sheet and ring wake (VSRW) model was developed to rapidly calculate the aerodynamic performance of wind turbines under axial steady conditions. The wake in the simplified FVW model is comprised of the vortex sheets in the near wake and the vortex rings, which are used to replace the helical tip vortex filament in the far wake. The position of the vortex ring is obtained by the motion equation of its control point. Analytical formulas of the velocity induced by the vortex ring were introduced to reduce the computational time of the induced velocity calculation. In order to take into account both accuracy and calculation time of the VSRW model, the length of the near wake was cut off at a 120° wake age angle. The simplified FVW model was used to calculate the aerodynamic load of the blade and the wake flow characteristic. The results were compared with measurement results and the results from the full vortex sheet wake model and the tip vortex wake model. The computational speed of the simplified FVW model is at least an order of magnitude faster than other two conventional models. The error of the low-speed shaft torque obtained from the simplified FVW model is no more than 10% relative to the experiment at most of wind speeds. The normal and tangential force coefficients obtained from the three models agree well with each other and with the measurement results at the low wind speed. The comparison indicates that the simplified FVW model predicts the aerodynamic load accurately and greatly reduces the computational time. The axial induction factor field in the near wake agrees well with the other two FVW models and the radial expansion deformation of the wake can be captured.

In the inner part of a large wind turbine blade, a thick airfoil is commonly used to guarantee structural integrity and assists the blade to run more easily at high angles of attack in variable winds; its local Reynolds number is less than 3.0 × 10⁶. Under these conditions, flow separation and transitions easily occur and exert great impact on blade performance. Vortex generators (VGs) are effective devices used to control flow separation and alter stalling conditions, and hence have been employed in the inner part of the blade in some wind turbines. To clearly understand the aerodynamic performance of a blade with VGs, a blade section employing the thick DU91-W2-250 airfoil and five pairs of VGs is modeled using the transition model. The results for both the coefficient of lift and drag–lift ratio predicted by the transition model are compared with those obtained from the k-ω shear stress transport model and experiment. The comparison demonstrates that the transition model has much higher accuracy. The effects of transition on the distributions of flow stream, shear stress, and vortices from the VGs are investigated and more useful rules are obtained through a comparison between the results of the transition model and the turbulence model at four angles of attack: 5°, 12°, 16°, and 20°.