Papers by Spyros Voutsinas
Journal of physics, May 1, 2022
A reduced order model of a floating wind turbine with 22 degrees of freedom has been implemented ... more A reduced order model of a floating wind turbine with 22 degrees of freedom has been implemented and validated in comparison to the multibody, hydro-servo-aero-elastic code hGAST. The multi-blade Coleman transformation is applied and Floquet stability analysis is performed. This allows on one hand, to verify the actual Floquet implementation against the standard Coleman-based eigenvalue analysis in cases the transformed dynamic system has constant coefficients and on the other hand to analyze the effects of different anisotropies on stability. Mass imbalance of the rotor and yaw misalignment have been specifically addressed. In the mass imbalance scenario, the homogeneous results are not substantially altered while in the wind yaw scenario, there is slight change of the flapwise natural frequencies and of the tower lateral frequency as well as of the corresponding damping characteristics.
Journal of Fluids and Structures
The fluid structure interaction of cylinders in tandem arrangement is used as validation basis of... more The fluid structure interaction of cylinders in tandem arrangement is used as validation basis of a multi-domain Lagrangian-Eulerian hybrid flow solver. In this hybrid combination, separate grids of limited width are defined around every solid body, on which the Eulerian flow equations are solved using finite volume approximations. In order to interconnect the domains defined by the grids, the entire flow is described in Lagrangian coordinates and the corresponding equations are solved via particle approximations in fully coupled mode with the solutions within the Eulerian grids. The flow solver is also strongly (implicitly) coupled with the structural dynamic equations in case the cylinders are elastically supported. In the present work, the Eulerian part solves the compressible flow equations in density-velocity-pressure formulation and uses pre-conditioning at low Ma while the Lagrangian part is based on the densitydilatation-vorticity-pressure formulation. The hybrid solver is first validated in the case of an isolated rigid cylinder at Re = 100. Then the case of a single elastically mounted cylinder at Re = 200 is considered, followed by the case of two cylinders in tandem arrangement that are either rigid or elastically mounted. Good agreement with results produced with spectral and immersed boundary methods is found indicating the capabilities of the hybrid predictions. Also the flexibility of the method in handling complex multi-body fluid structure interaction problems is demonstrated by allowing grid-overlapping.
Journal of Marine Science and Engineering, 2020
Accurate and efficient numerical wave generation and absorption of two-dimensional nonlinear peri... more Accurate and efficient numerical wave generation and absorption of two-dimensional nonlinear periodic waves traveling on a steady, uniform current were carried out in a potential, fully nonlinear numerical wave tank. The solver is based on the Βoundary Εlement Μethod (ΒΕΜ) with linear singularity distributions and plane elements and on the mixed Eulerian–Lagrangian formulation of the free surface equations. Wave generation is implemented along the inflow boundary by imposing the stream function wave solution, while wave absorption at both end-boundaries is effectively treated by introducing absorbing layers. On the absorbing beach side, the outflow boundary condition is modified to ensure that the solution accurately satisfies the dispersion relation of the generated waves. The modification involves a free-parameter that depends on the mass flux through the domain and is determined through a feedback error-correction loop. The developed method provides accurate time domain wave solu...
Energies, 2021
The present paper deals with the development of a multi-purpose floating tension leg platform (TL... more The present paper deals with the development of a multi-purpose floating tension leg platform (TLP) concept suitable for the combined offshore wind and wave energy resources exploitation, taking into account the prevailing environmental conditions at selected locations along the European coastline. The examined Renewable Energy Multi-Purpose Floating Offshore System (REFOS) platform encompasses an array of hydrodynamically interacting oscillating water column (OWC) devices, moored through tensioned tethers as a TLP platform supporting a 10 MW wind turbine (WT). The system consists of a triangular platform supported by cylindrical floaters, with the WT mounted at the deck’s center and the cylindrical OWC devices at its corners. Details of the modelling of the system are discussed and hydro-aero-elastic coupling between the floater; the mooring system; and the WT is presented. The analysis incorporates the solutions of the diffraction; the motion- and the pressure-dependent radiation ...
The operation of a floating wind turbine is consider ed in half wake conditions. To this end the ... more The operation of a floating wind turbine is consider ed in half wake conditions. To this end the free -wake version of hGAST is used which simulates blades as lifting -surfaces that generate the wake in the form of freely moving vortex blobs. Reference results are obtained by simultaneously simulating both wind turbines (WTs). The wake of the preceding WT is allowed to evolve until the second one is fully submerged in it. Also in view of formulating less expensive simulations each WT is considered separately ; the wake of the preceding WT is processed to give mean wake profiles that are then used as input to the second one. Results are presented and compared for the OC3 spar buoy floating wind turbine.
The paper describes the objectives and the structure of the GARTEUR Action Group HC/AG-22 project... more The paper describes the objectives and the structure of the GARTEUR Action Group HC/AG-22 project which deals with the basic research about the forces acting on obstacles when immersed in rotor wakes. The motivation started from the observation that there was a lack of experimental databases including the evaluation of the forces on obstacles in rotor wakes; and of both numerical and experimental investigations of the rotor downwash effects at medium-to-high Separation distances from the rotor, in presence or without sling load. The four research centres: CIRA (I); DLR (D); NLR (NL); ONERA (F); and three universities: NTUA (GR); Politecnico di Milano (I); University of Glasgow (UK) created a team for the promotion of activities that could contribute to fill these gaps. In particular, both numerical and experimental investigations were proposed by the team to study, primarily, the effects of the confined area geometry on a hovering helicopter rotor, and, secondarily, the downwash and...
The effects of a wind turbine wake on General Aviation and the behaviour of helicopters in the ti... more The effects of a wind turbine wake on General Aviation and the behaviour of helicopters in the tip vortex of large fixed-wing aircraft has been topic of research in the past years, but less is known about the interactions of helicopters operating in a wind turbine wake. A dedicated GARTEUR Action Group, HC-AG23, consisting of European universities and research institutes was formed to investigate helicopter behaviour in a wind tur-bine wake and to study the consequences for helicopter handling and safety of flight. The activities are struc-tured in work packages addressing wind turbine wake identification, wake experiments and computations, offline and piloted simulations and management and dissemination activities. This paper presents an over-view of the partners’ activities and provides a short overview of the results that have been achieved in the past three years.
Renewable Energy, 2019
Today, Vortex Generators (VGs) are becoming an integral part of a Wind Turbine blade design. Howe... more Today, Vortex Generators (VGs) are becoming an integral part of a Wind Turbine blade design. However, the challenges involved in the computation of the flow around VGs are yet to be dealt with in a satisfactory manner. A large number of VG models for Reynolds Averaged Navier Stokes (RANS) solvers has been proposed and, among them, the BendereAndersoneYagle (BAY) model (ASME Pap. FEDSM99-6919) is one of the most popular, due to its ease of use and relatively low requirements for user input. In the present paper a thorough investigation on the performance and application of the BAY model for aerodynamic VG flows is presented. A fully resolved RANS simulation is validated against experiments and then used as a benchmark for the BAY model simulations. A case relevant to wind turbines is examined, which deals with the flow past a wind turbine airfoil at Reynolds number 0.87e6. When the grid related errors are excluded, it is found that the generated vortices are weaker in the BAY model simulations than in the fully resolved computation. The latter finding is linked to an inherent deficiency of the model, which is first found in this study and which is explained in detail.
Journal of Physics: Conference Series, 2016
The current paper presents the effort, in the EU AVATAR project, to establish the necessary requi... more The current paper presents the effort, in the EU AVATAR project, to establish the necessary requirements to obtain consistent lift over drag ratios among seven CFD codes. The flow around a 2D airfoil case is studied, for both transitional and fully turbulent conditions at Reynolds numbers of 3 × 10 6 and 15 × 10 6. The necessary grid resolution, domain size, and iterative convergence criteria to have consistent results are discussed, and suggestions are given for best practice. For the fully turbulent results four out of seven codes provide consistent results. For the laminar-turbulent transitional results only three out of seven provided results, and the agreement is generally lower than for the fully turbulent case.
Journal of Physics: Conference Series, 2016
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Coastal Engineering Proceedings, 2012
The knowledge of the behavior of floating offshore wind turbines (W/T) under wave and/or wind act... more The knowledge of the behavior of floating offshore wind turbines (W/T) under wave and/or wind action remains one of the most difficult challenges in offshore engineering which is mostly due to the highly non-linear response of the structure. The present study describes the design process of a 3D physical experiment to investigate the behavior of the most promising structure technology of floating W/T: spar buoy (SB) and tension leg platform (TLP) under different meteo conditions. In order to properly design the two W/T models, the following topics have been analyzed: mooring lines, mass distribution, appropriate scaling factor and data relative to the geometrical characteristics, wave basin dimensions and wind and waves conditions. In addition, the Smoothed Particle Hydrodynamics method (SPH) (Monaghan 1994) has been considered to simulate the 3D behavior of a floating offshore W/T. In particular, the SPH, calibrated and verified on the basis of the experimental observations, may re...
ESAIM: Proceedings, 1996
Low-Mach-number aeroacoustic theories are applied to predict far-eld sound emission from vortex-d... more Low-Mach-number aeroacoustic theories are applied to predict far-eld sound emission from vortex-dominated ows. The latter are simulated using three-dimensional vortex methods. Both particle schemes and lament-based schemes are used. Comparisons of model predictions with theoretical and experimental results on the interaction of two v ortex rings are rst discussed. Next, the schemes are used to examine the e ect of initial conditions and 3D perturbations on the properties of the far-eld acoustic pressure. Finally, a more elaborate wind-turbine model is presented and its application to the evaluation of several turbine-blade designs is summarized.
Journal of Physics: Conference Series, 2016
The FP7 AdVanced Aerodynamic Tools for lArge Rotors-Avatar project aims to develop and validate a... more The FP7 AdVanced Aerodynamic Tools for lArge Rotors-Avatar project aims to develop and validate advanced aerodynamic models, to be used in integral design codes for the next generation of large scale wind turbines (10-20MW). One of the approaches towards reaching rotors for 10-20MW size is the application of flow control devices, such as flaps. In Task 3.2: Development of aerodynamic codes for modelling of flow devices on aerofoils and rotors of the Avatar project, aerodynamic codes are benchmarked and validated against the experimental data of a DU95W180 airfoil in steady and unsteady flow, for different angle of attack and flap settings, including unsteady oscillatory trailing-edge-flap motion, carried out within the framework of WP3: Models for Flow Devices and Flow Control, Task 3.1: CFD and Experimental Database. The aerodynamics codes are: AdaptFoil2D, Foil2W, FLOWer, MaPFlow, OpenFOAM, Q 3 UIC, ATEFlap. The codes include unsteady Eulerian CFD simulations with grid deformation, panel models and indicial engineering models. The validation cases correspond to 18 steady flow cases, and 42 unsteady flow cases, for varying angle of attack, flap deflection and reduced frequency, with free and forced transition. The validation of the models show varying degrees of agreement, varying between models and flow cases.
Applied Sciences, 2021
The interaction of a helicopter rotor with the ground in hover flight is addressed numerically us... more The interaction of a helicopter rotor with the ground in hover flight is addressed numerically using a hybrid Eulerian–Lagrangian CFD model. When a helicopter takes off or lands, its wake interferes with the ground. This interaction, depending on the height-to-rotor diameter ratio, causes the altering of the rotor loading and performance as compared to the unconstrained case and gives rise to the development of a complex outwash flow field in the surrounding of the helicopter. The present study aims to characterize the interactional phenomena occurring in the early stages of the rotor wake development and in particular the interference of the starting vortex with the ground boundary layer and the effect of this interaction in the motion of the vortex in the rotor outwash flow. The hybrid CFD method employed combines a standard URANS compressible finite volume solver, the use of which is restricted to confined grids around solid bodies, and a Lagrangian approximation of the entire fl...
Fluids
A fully coupled hydro-servo-aero-elastic simulator for the analysis of floating offshore wind tur... more A fully coupled hydro-servo-aero-elastic simulator for the analysis of floating offshore wind turbines (FOWTs) is presented. All physical aspects are addressed, and the corresponding equations are concurrently solved within the same computational framework, taking into account the wind and wave excitations, the aerodynamic response of the rotor, the hydrodynamic response of the floater, the structural dynamics of the turbine-floater-mooring lines assembly and finally the control system of the wind turbine. The components of the complex multi-physics system of a FOWT interact with each other in an implicitly coupled manner leading to a holistic type of modeling. Different modeling options, of varying fidelity and computational cost, are made available with respect to rotor aerodynamics, hydrodynamic loading of the floater and mooring system dynamics that allow for timely routine certification simulations, but also for computationally intense simulations of less conventional operating...
Journal of Physics: Conference Series
Mediterranean Marine Science
This paper summarizes the coupled hydro-aero-elastic analysis of a multi-purpose floating structu... more This paper summarizes the coupled hydro-aero-elastic analysis of a multi-purpose floating structure suitable for offshore wind and wave energy exploitation. The analysis incorporates properly the solutions of the diffraction and the pressure- and motion- dependent radiation problems around the floating structure and the aerodynamics of a 5 MW Wind Turbine (WT). Finite water depths are considered, the structure being floating under the action of regular surface waves. The platform encompasses three hydrodynamically interacting Oscillating Water Column (OWC) devices consisting of concentric vertical cylinders, moored through tensioned tethers in a TLP concept. Details concerning the numerical and experimental modelling of the system are presented and the numerical results are compared against experimental data.
Journal of Physics: Conference Series
The local manufacturing of small wind turbines has become increasingly popular over the last deca... more The local manufacturing of small wind turbines has become increasingly popular over the last decade, among international networks of renewable energy practitioners, for the implementation of rural electrification applications. Locally manufactured small wind turbines (LMSWTs), used most frequently in off-grid battery based renewable energy systems, typically utilize wooden blades and coreless axial flux permanent magnet generators due to their simple manufacturing process and local availability of materials. In this paper the effects of leading edge erosion on locally manufactured small wind turbine blades are researched experimentally, both in terms of power performance and acoustic noise emissions. From the research it is concluded that a yearly maintenance of the wooden blades of a LMSWT can lead to less acoustic noise emissions and better power performance, with the latter becoming more significant as the mean wind speed of the installation site increases. For practitioners, installers and manufacturers of LMSWTs, these findings can significantly guide manufacturing processes and techniques in terms of preventing leading edge erosion, while also advising preventative maintenance procedures on the field, in order to keep small wind electric systems quiet and productive.
Aerospace Science and Technology
Journal of Wind Engineering and Industrial Aerodynamics, 2016
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Papers by Spyros Voutsinas