Rolling element bearing faults of a laboratory scale wind turbine gearbox operating under nonstationary loads have been diagnosed using condition monitoring (CM) techniques such as vibration analysis, acoustic analysis, and lubrication oil analysis. Two local bearing faults, namely, bearing inner race fault and bearing outer fault are seeded in the gearbox. The raw data from these techniques are decomposed and wavelet approximation coefficients of level four (a4) are extracted using discrete wavelet transform (DWT). A plethora of statistical features is computed from the wavelet approximation coefficients and the most significant features are being identified by implementing the decision tree algorithm. The classification efficiencies of each of these CM techniques are compared by using the support-vector machine algorithm. Furthermore, an integrated CM scheme is developed by combining the individual CM techniques and the fault diagnosing ability of the integrated CM scheme is compared with the individual CM techniques. A principal component analysis-based approach is used as a feature classification algorithm and an input feature matrix is formed by combining the significant features extracted from vibration, acoustic, and lubrication oil analysis. It has been observed that the integrated CM scheme has provided better classification interpretations than the single CM techniques and it can be extended for real time fault diagnosis of a wind turbine gearbox.

Diffuser augmented wind turbines (DAWTs) are incredibly beneficial to low wind speed areas. The duct that surrounds the turbine improves the power output by accelerating the approaching wind directing the wind through the blade. The power output of DAWT mainly depends on the duct length by turbine diameter (L/D) ratio, duct angle, axial distance, and tip clearance between the blade and duct. This article gives an insight into the performance variation of DAWT for various duct L/D ratios. Numerical simulations were performed on DAWT using ANSYS FLUENT and the performance characteristics were studied for different duct L/D ratios, duct angles, and axial distance. The investigations found that axial distance of 0.06 D for duct L/D ratios between 0.15 to 0.60 gives improved performance. It was found that the optimal duct angle is a function of the L/D ratio, and as the L/D ratio increases, the duct angle increases. A geometric procedure was used to find the pattern in which the angle increases in other L/D ratios. The geometric procedure helps to keep the duct's inner profiles merging for duct L/D ratios 0.15 to 0.6 by maintaining constant axial distance. By keeping the ducts as per the proposed procedure resulted in angles 22 deg, 38 deg, 45 deg, and 52 deg for duct L/D = 0.15, 0.3, 0.45 and 0.6. The performance of WT with 30 deg angled ducts and proposed angled ducts were compared. The proposed angled ducts had improved power output than 30 deg angled ducts. The proposed axial distance and duct angles help to use the duct length effectively, which shortens the duct and enhances power output.

Numerical simulations were performed for two-dimensional viscous incompressible flow past two stationary side by side circular cylinders at Reynolds number (Re) 100 by varying centre to centre distance between the cylinders from 1.1 to 8 times the diameter (D) of a cylinder. The incompressible Navier-Stokes equations were solved using a finite volume method. Five different flow regimes were observed in the flow as the distance between the cylinders was increased systematically. An attempt has been made to characterise the different flow regimes using different numerical tools like Proper Orthogonal Decomposition (POD), λ2 criterion, instantaneous streamwise normal stress produced due to periodic variation of flow, frequency spectrum analysis and phase diagrams. All these tools confirm the clear existence of five different regimes in the flow when the gap between the cylinders is varied over the above stated range.

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