Viscous and Aeroelastic Effects on Wind Turbine Blades. The VISCEL Project. Part II: Aeroelastic Stability Investigations

The recent introduction of ever larger wind turbines poses new challenges with regard to understanding the mechanisms of unsteady flow–structure interaction. An important aspect of the problem is the aeroelastic stability of the wind turbine blades, especially in the case of combined flap/lead–lag vibrations in the stall regime. Given the limited experimental information available in this field, the use of CFD techniques and state‐of‐the‐art viscous flow solvers provides an invaluable alternative towards the identification of the underlying physics and the development and validation of sound engineering‐type aeroelastic models. Navier–Stokes‐based aeroelastic stability analysis of individual blade sections subjected to combined pitch/flap or flap/lead–lag motion has been attempted by the present consortium in the framework of the concluded VISCEL JOR3‐CT98‐0208 Joule III project. Copyright © 2003 John Wiley & Sons, Ltd.     

Wind turbine rotor‐tower interaction using an incompressible overset grid method

In this paper, 3D Navier–Stokes simulations of the unsteady flow over the NREL Phase VI turbine are presented. The computations are carried out using the structured grid, incompressible, finite volume flow solver EllipSys3D, which has been extended to include the use of overset grids. Computations are presented, firstly, on an isolated rotor, and secondly, on the downwind configuration of the turbine, which includes modelling of the rotor, tower and tunnel floor boundary. The solver successfully captures the unsteady interaction between the rotor blades and the tower wake, and the computations are in good agreement with the experimental data available. The interaction between the rotor and the tower induces significant increases in the transient loads on the blades and is characterized by an instant deloading and subsequent reloading of the blade, associated with the velocity deficit in the wake, combined with the interaction with the shed vortices, which causes a strongly time‐varying response. Finally, the results show that the rotor has a strong effect on the tower shedding frequency, causing under certain flow conditions vortex lock‐in to take place on the upper part of the tower. Copyright © 2009 John Wiley & Sons, Ltd.     

Dynamic stall analysis using harmonic balance and correlation‐based γ– transition models for wind turbine applications

In this paper, we use the harmonic balance method to study an oscillating S809 airfoil in dynamic stall. The periodic behavior of this problem makes it well suited for the harmonic balance method, which is able to model unsteady aerodynamics at greatly reduced computational costs when compared with time‐accurate unsteady‐flow solvers. A finite‐volume technique based on the lower–upper symmetric Gauss–Seidel scheme with Roe fluxes is used to solve the Reynolds‐averaged Navier–Stokes equations. The turbulent viscosity is computed with the one‐equation Spalart–Allmaras turbulence model. In addition, the laminar–turbulent transition is modeled using a correlation‐based approach originally developed by Langtry and Menter. Comparisons with experimental data for steady flows with the S809 airfoil highlight the necessity of the transition model to accurately predict the onset of static stall. For unsteady cases, the transition model provides improved agreement with experimental data, predicting dynamic stall when the fully turbulent model cannot. Copyright © 2014 John Wiley & Sons, Ltd.     

Non-noble metal composite cathodes for hydrogen evolution. Part I: The Ni–MoOx coatings electrodeposited from Watt’s type bath containing MoO3 powder particles

In this work the Ni-MoO_x coatings have been prepared and characterized in view of their possible application as electrocatalysts for hydrogen evolution reaction (HER) in alkaline solution. The procedure of deposition of Ni-MoO_x coatings from the Watt’s type bath containing MoO₃ powder particles onto Ni mesh, under the conditions of simulated industrial deposition conditions for commercial cathodes, has been presented. The morphology of the obtained coatings was investigated by SEM, the composition by EDS and the phase composition by XRD techniques. The polarization characteristics for hydrogen evolution on the obtained Ni-MoO_x coatings were investigated in the 32 wt.% NaOH at 90 °C and compared with the one recorded for the commercial De Nora’s coating (DN). It was shown that the best Ni-MoO_x coating exhibits almost identical polarization characteristics as the commercial one. By the cross section and XRD analysis of deposited samples it was confirmed that MoO₃ powder particles were not occluded by the Ni deposit and that molybdenum species were deposited from the molybdate ions formed by dissolution of MoO₃, following the mechanism of induced co-deposition. The reaction mechanism for MoO₃ phase deposition has also been proposed.     

The kinetic behaviour of ion transport in WO3 based films produced by sputter and sol–gel deposition:: Part I. The simulation model

This paper develops a new simulation model for charge injection and extraction in electrochromic WO₃ films under conditions of constant current during the charge injection process. The model is applied to the constant current coloration and bleaching of electrochromic films, and values for the diffusion coefficient and other model parameters have been obtained by fitting the model to experimental data. Application of the model to coloration and bleaching of electrochromic devices is discussed, in particular the use of the model in the design of electrochromic switching schemes.