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Blade leading edge erosion is acknowledged to significantly reduce the energy yield of wind turbines. The problem is particularly severe for offshore installations, due to faster erosion progression boosted by harsh environmental conditions. This study presents and demonstrates an experimentally validated simulation-based technology for rapidly and accurately estimating wind turbine energy yield losses due to general leading edge erosion. The technology combines the predictive accuracy of two- and three-dimensional Navier-Stokes computational fluid dynamics with the runtime reductions enabled by artificial neural networks and wind turbine engineering codes using the blade element momentum theory. The main demonstration is based on the assessment of the annual energy yield of the National Renewable Energy Laboratory 5 MW reference turbine affected by leading edge erosion damage of increasing severity, considering damages based on available laser scans and previous leading edge erosion analysis. Results also include sensitivity studies of the energy loss to the wind characteristics of the installation site. It is found that the annual energy loss varies between about 0.3 and 4%, depending on the damage severity and the site wind characteristics. The study also illustrates the necessity of resolving the geometry of eroded leading edges rather than accounting for the effects of erosion with surrogate models, since, after an initial increase of distributed surface roughness, erosion yields leading edge geometry alterations causing aerodynamic losses exceeding those due to the loss of boundary layer laminarity consequent to roughness-induced transition. The presented technology enables estimating in a few minutes the amount of energy lost to erosion for many-turbine wind farms, and offers a key tool for predictive maintenance.

We present an unsteady simulation of an axial fan with low pressure and high flow rate, developed during the MinWaterCSP EU project, specifically designed and optimized for Concentrating Solar Power (CSP) plants with the aim of reducing water consumption at the condenser stage. An earlier version of the fan, referred as M-fan, was initially developed to serve the hybrid cooling system, to boost the overall heat transfer performance with dry cooling. In this work, we will performing a Computational Fluid Dynamics (CFD) analysis of the unsteady flow on a redesigned and scaled version of the M-fan, referred as T-fan, by The T-fan was designed and optimized to reduce noise emissions and improve efficiency with respect to the M-fan. We perform the simulation using an in-house built C++ parallel code for CFD analysis using Finite Elements (FE). We model the flow dynamics using the Residual Based Variational MultiScale method (RBVMS) to obtain a stabilized solution of the Navier-Stokes equation using FE discretization. We will discuss the simulation results of the RBVMS model by comparing our simulation of the T-fan with experimental results on the same fan.

Rain erosion of wind turbine blades represents an interesting topic of study due to its non-negligible impact on annual energy production of the wind farms installed in rainy sites. A considerable amount of recent research works has been oriented to this subject, proposing rain erosion modelling, performance losses prediction, structural issues studies, etc. This work aims to present a new method to predict the damage on a wind turbine blade. The method is applied here to study the effect of different rain conditions and blade coating materials, on the damage produced by the rain over a representative section of a reference 5MW turbine blade operating in normal turbulence wind conditions.

The detailed prediction of the upcoming wind on wind farms can support optimization of wind energy production and operation and maintenance. Numerical Weather Prediction (NWP) tools allow to simulate the wind over long-term forecasting horizons (up to several days) with a spatial resolution ranging between the continental level down to a few hundred meters. We present a methodology, based upon Computational Fluid Dynamics (CFD) and Reynolds Averaged Navier Stokes (RANS) modelling, that allows to downscale the spatial resolution of the wind prediction supplied by a NWP model down to the typical length-scale of wind energy applications. The proposed approach combines a number of standard tools, including: Geographical Information Systems (GIS), Advanced Research - Weather Research and Forecasting (WRF-ARW) and OpenFOAM, and proposes methods to interface these tools and set-up the local-scale simulation. Models and problem sizes are selected to keep the computational cost of the system sustainable in view of its implementation in operational forecasting. Finally, we present the application of the method on a given onshore site, and for three different meteorological conditions, showing the potential of the approach, but also giving an account of the limitations that it may encounter when dealing with complex planetary boundary layers.

Computational fluid–structure interaction (FSI) and flow analysis now have a significant role in design and performance evaluation of turbomachinery systems, such as wind turbines, fans, and turbochargers. With increasing scope and fidelity, computational analysis can help improve the design and performance. For example, it can help add a passive morphing attachment (MA) to the blades of an axial fan for the purpose of controlling the blade load and section stall. We present a stabilized Arbitrary Lagrangian–Eulerian (ALE) method for computational FSI analysis of passive morphing in turbomachinery. The main components of the method are the Streamline-Upwind/Petrov–Galerkin (SUPG) and Pressure-Stabilizing/Petrov–Galerkin (PSPG) stabilizations in the ALE framework, mesh moving with Jacobian-based stiffening, and block-iterative FSI coupling. The turbulent-flow nature of the analysis is handled with a Reynolds-Averaged Navier–Stokes (RANS) model and SUPG/PSPG stabilization, supplemented with the “DRDJ” stabilization. As the structure moves, the fluid mechanics mesh moves with the Jacobian-based stiffening method, which reduces the deformation of the smaller elements placed near the solid surfaces. The FSI coupling between the blocks of the fully-discretized equation system representing the fluid mechanics, structural mechanics, and mesh moving equations is handled with the block-iterative coupling method. We present two-dimensional (2D) and three-dimensional (3D) computational FSI studies for an MA added to an axial-fan blade. The results from the 2D study are used in determining the spanwise length of the MA in the 3D study.

The concept of morphing geometry to control and stabilize the flow has been proposed and applied in several aeronautic and wind turbine applications. We studied the effect of a similar passive system applied on an axial fan blade, analysing potential benefits and disadvantages associated to the passive coupling between fluid and structure dynamics. The present work completes a previous study made at the section level, giving a view also on the three-dimensional effects. We use the numerical computation to simulate the system which defines a complex fluid-structure interaction problem. In order to do that, an in-house finite element solver, already used in the previous study, is applied to solve the coupled dynamics.

Numerical simulation tools are acquiring a crucial role in the virtual prototyping of new fan rotor blades. This, considering also the possibility in using new advanced materials, is opening the design capability to blades of longer, lighter and more slender structure. On this perspective, the numerical tools must be improved in order to catch also the non-linear and coupling phenomena which were been treated until now using a weak coupling approach. Here we present a fluid-structure interaction solver based on the finite element method, through its application to an existing fan blade. The study will show how, even in case of metal structure with little deformation, the coupling between fluid dynamics and structure dynamics can produce effects on both the fluid and the solid involved in the machine main process. The possibility to simulate directly both the aerodynamic and the effective structure response opens the way to improved design capabilities, avoiding time waste and costs due to long experimental testing campaign and over-dimensioned structures.

Wind-turbine blades exposed to rain can be damaged by erosion if not protected. Although this damage does not typically influence the structural response of the blades, it could heavily degrade the aerodynamic performance, and therefore the power production. We present a method for computational analysis of rain erosion in wind-turbine blades. The method is based on a stabilized finite element fluid mechanics formulation and a finite element particle-cloud tracking method. Accurate representation of the flow would be essential in reliable computational turbomachinery analysis and design. The turbulent-flow nature of the problem is dealt with a RANS model and SUPG/PSPG stabilization, the particle-cloud trajectories are calculated based on the flow field and closure models for the turbulence–particle interaction, and one-way dependence is assumed between the flow field and particle dynamics. The erosion patterns are then computed based on the particle-cloud data.

Wind-turbine blade rain erosion damage could be significant if the blades are not protected. This damage would not typically influence the structural integrity of the blades, but it could degrade the aerodynamic performance and therefore the power production. We present computational analysis of rain erosion in wind-turbine blades. The main components of the method used in the analysis are the Streamline-Upwind/Petrov–Galerkin (SUPG) and Pressure-Stabilizing/Petrov–Galerkin (PSPG) stabilizations, a finite element particle-cloud tracking method, and an erosion model. The turbulent-flow nature of the analysis is handled with a RANS model and SUPG/PSPG stabilization, the particle-cloud trajectories are calculated based on the computed flow field and closure models defined for the turbulent dispersion of particles, and one-way dependence is assumed between the flow and particle dynamics. The erosion patterns are then computed based on the particle-cloud data. The patterns are consistent with those observed in the actual wind turbines.

The morphing geometry concept finds interesting applications in load reduction and performance increasing for wings and rotor blades in off-design conditions. Here we report a numerical study on the effect that a passive morphing system (made by an elastic-low stiffness surface) has on the sectional load and flowfield, when it is applied to the trailing edge of an axial fan. We obtain the results extracting the section of the fan blade and test it in the 2D cascade, with and without the elastic device, in different operating conditions. Keeping in mind the two-dimensional approximation, it will be possible to observe how the tested device could reduce the load in off-design and high angle of attack conditions, while the same solution could introduce vibrations in design conditions. All the simulations imply the solution of the fluid-structure interaction between the incompressible, turbulent flow and the elastic structure. This solution is obtained using a finite element based, strongly coupled solver, applied to the periodic 2D domain of the section in the cascade.

Numerical tools aiming at the evaluation of ground acoustic impact of helicopters typically rely on databases given in terms of acoustic disturbance over hemispheres surrounding the helicopter (noise hemispheres). These are evaluated for a discrete number of steady flights falling within the flight envelope. The objective of the present work is the identification of flight parameters to be considered for the characterization of noise hemispheres, particularly when related to unsteady maneuvers. To this purpose, different approaches based on steady flight aeroelastic/aerodynamic/aeroacoustic predictions are examined for assessing their capability of simulating the acoustic impact of helicopters in arbitrary unsteady flight. The numerical investigation demonstrates that at least three parameters, including disk loading, are required to adequately characterize noise hemispheres. Conversely, the similarity of kinematic parameters alone may yield steady flight acoustic predictions poorly correlated with those obtained for unsteady maneuvers.

The actual strategy in offshore wind energy development is oriented to the progressive increase of the turbine diameter as well as the per unit power. Among many pioneering technological and aerodynamic issues linked to this design trend, the wind velocity at the blade tip region reaches very high values in normal operating conditions (typically between 90 to 110 m/s). In this range of velocity, the rain erosion phenomenon can have a relevant effect on the overall turbine performance in terms of power and energy production (up to 20% loss in case of deeply eroded leading edge). Therefore, as a customary approach erosion related issues are accounted for in the scheduling of the wind turbine maintenance. When offshore, on the other hand, the criticalities inherent to the cost of maintenance and operation monitoring suggest the rain erosion concerns to be tackled at the turbine design stage. In so doing, the use of computational tools to study the erosion phenomenon of wind turbines under severe meteorological conditions could define the base-line approach in the wind turbine blades design and verification. In this work, the authors present a report on numerical prediction of erosion on a 6 MW HAWT (horizontal axis wind turbine). Two different blade geometries of different aerodynamic loading, have been studied in a view to explore their sensitivity to rain erosion. The fully 3D simulations are carried out using an Euler-Lagrangian approach. Flow field simulations are carried out with the open-source code OpenFOAM, based on a finite volume approach, using Multiple Reference Frame methodology. Reynolds Averaged Navier-Stokes equations for incompressible steady flow were solved with a k-ε turbulence. An in-house code (P-Track) is used to compute the rain drops transport and dispersion, adopting the Particle Cloud Tracking approach (PCT), already validated on large industrial turbomachinery. At the impact on blade, erosion is modelled accounting for the main quantities affecting the phenomenon, which are impact velocity and material properties of the target surface. Results provide the regions of the two blades more sensitive to erosion, and the effect of the blade geometry on erosion attitude.