Home/AA. Aerodynamics and Aeroacoustics/AA. Aerodynamics and Aeroacoustics – Posters

The Science of Making Torque from Wind (TORQUE 2018)

20 June  |  21 June  |  22 June  |  Events View
AA | CM | DSE | MET | MST | WWT

Loading Events
This event has passed.

Room: BL.27 Building
Topic: AA. Poster Session
Form of presentation: Poster
Duration: 75 minutes

Authors:
Krzysztof Rogowski, Martin Otto Laver Hansen, Rolf Hansen, Janusz Piechna, Piotr Lichota

Abstract:
This paper presents numerical investigation of the DU91 airfoil at Reynolds number of 3 million for two angles of attack -0.04o and 7.08o. The measurement have been done at the LM Wind Power Low Speed Wind Tunnel. The lift and drag are obtained from airfoil pressure and wake rake respectively. The unsteady flow over the airfoil is investigated by means of a detached eddy simulation (DES) with the transition SST turbulence model. The lift and drag coefficients are obtained using ANSYS Fluent. It is concluded that the results of the pressure distribution around the airfoil and the aerodynamic coefficients are in agreement with the experiment

Authors:
Junheng Feng, Bofeng Xu, Zhenzhou Zhao, Yue Yuan

Abstract:
In this paper, a novel trailing edge flap structure is designed based on wind turbine airfoil S809. The aerodynamic performance and the flow field of the proposed trailing edge flap airfoil are predicted by the computational fluid dynamics(CFD) method at the angles of attack of -5~12.5 degrees. The lift coefficient, drag coefficient, pressure contour and streamline distribution of the proposed trailing edge flap airfoil are analyzed and compared with the traditional flaps. The results illustrated that the lift coefficient and the lift-to-drag ratio of the novel trailing edge flap are obviously larger than that of the traditional flaps, and the novel trailing edge flap can effectively improve the stall characteristics of the airfoil trailing edge.

Authors:
Matias Sessarego, Nestor Ramos-Garcia, Wen Zhong Shen

Abstract:
An in-house aero-elastic vortex code, called MIRAS, is used to investigate the aerodynamic performance of winglets and sweep on horizontal-axis wind turbine (HAWT) blades in simple and complex inflow conditions. Previous studies using vortex codes applied to study winglets and blade sweep on HAWTs have typically not considered complex inflow conditions such as turbulent wind and shear. The reasons may include the absence of modeling capability, the computational cost associated with simulating long turbulent time series, and/or the computational cost associated with resolving the blade tips to a very fine level. A preliminary study is performed here, where the MIRAS code is applied on the NREL 5 MW wind turbine with an arbitrary winglet shape and blade sweep. Results indicate that wind turbine blades with sweep or winglets might be better in performance compared to their straight blade counterparts.

Authors:
Tim Lehmann, Marc S. Schneider, Ulrike Kersten

Abstract:
In this work the unsteady aerodynamic loads predicted by methods of various fidelity are compared. These are a strip theory model based on the analytical theories by Greenberg and Loewy, an Euler and a RANS CFD simulations. The test object is the DTU 10 MW reference wind turbine. The comparison uses transfer functions derived with a blade torsion, and bending deformation in flap-wise and edge-wise direction as the input, aerodynamic loads as the output. The temporal discretization and simulation time of the CFD has to be chosen carefully as it influences the transfer behavior, the RANS simulation is taken as a baseline. The transfer functions are compared over a range of flow conditions. Considering the reduced calculation time, the Euler simulation is very accurate for most flow conditions. The accuracy of the strip theory is reasonable when a torsion or a flap-wise deflection is applied, but limited for edge-wise deflections.

Authors:
Sonia Rullaud, Frédéric Blondel

Abstract:
In the present work, LaBoheMe, a 2D actuator-line wind turbine model coupled with a Lattice Boltzmann Method (LBM) is presented. The basic idea is to perform reliable wind turbine simulations, thanks to a second order accurate, viscous, low diffusion framework: the LBM. The solver is validated on analytical cases (Backward Facing Step, BFS) and Vertical Axis Wind Turbine (VAWT) forces and wake measurements. LaBoheMe is currently limited to 2D simulations, but the extension to 3D should be straightforward.

Authors:
Giorgia Guma, Galih Bangga, Eva Jost, Thorsten Lutz, Ewald Krämer

Abstract:
WINSENT (Wind Science and Engineering in complex Terrain) is the German collaborative project to examine the characteristics of wind turbines in complex terrain. A terrain is defined complex when its roughness and orography is influencing the atmospheric boundary layer. Two research wind turbines with a rotor diameter of around 50 m diameter and 750 kW each are planned to be erected in Stöttener Berg, a location in southern Germany. The development of new numerical models is necessary in order to evaluate performances and aeroelastic effects. In particular, different project partners will use different approaches, going from CFD-CSD to BEM based calculations. In order to be able to compare them, it is necessary to have consistent and properly derived input data. In particular, BEM calculations need separately determined airfoil polars. Aerodinamic 3D effects are usually considered by empirical corrections of the polars while in 3D CFD calculations, these effects are entirely part of the solution.

Authors:
Galih Bangga, Thorsten Lutz, Ewald Krämer

Abstract:
The present works aim to investigate the effectiveness of active separation control by means of combined suction and vortex generator jets on the suction side of a very thick airfoil (40%) under tripped conditions. Two turbulence models were applied, namely URANS and DDES, to assess the consistency of the results. It is observed for the baseline case that URANS simulations are too optimistic while DDES delivers an excellent agreement with the available experiment at  = 20°. The studies reveal that the proposed system is able to delay separation significantly, increasing the overall aerodynamic performance of the airfoil.

Authors:
Amr M. Halawa, Matias Sessarego, Wen Zhong Shen, Shigeo Yoshida

Abstract:
The development of reliable Fluid-Structure Interaction (FSI) simulation tools and models for the wind turbines is a critical step in the design procedure towards achieving optimized large wind turbine structures. Such approach will mitigate the aeroelastic instabilities like: torsional utter, stall utter and edgewise instability that introduce extra stresses to the turbine structure leading to reduced life time and substantial failures. In this study, FSI simulations were held using the commercial package Ansys v18.2 solvers as a preliminary step towards our on-going development of a reliable Open-Source solver. These simulations were applied to the full-scale rotor blades of the NREL 5MW reference horizontal axis wind turbine. The aerodynamic loads and structural responses computations were carried out using a steady-state FSI analysis. The computations were run on the Kyushu University multi-core Linux cluster using the public domain openMPI implementation of the standard message passing interface (MPI). Finally, the results were validated against the Technical University of Denmark’s (DTU) MIRAS aeroelastic code results as well as the widely used FLEX5-Q3UIC and FAST codes in different cases showing reasonable agreement.

Authors:
Daniel Micallef, Tonio Sant

Abstract:
The aerodynamic effects resulting from a sheared inflow become even more relevant with modern large scale rotors. A major implication of a sheared wind profile is that it causes an out-of-plane moment about the rotor plane horizontal axis. This has not been satisfactorily addressed in the literature. The aims of this work are to (i) quantify the upward vertical shift in the line of action of the thrust with respect to the rotor center and (ii) to investigate the wake causes a restoring out-of-plane moment. The NREL 5MW reference turbine is used as reference with a power law wind profile as an inflow condition. Simulations are carried out using an open source lifting line free-wake vortex model and cross-compared with the results from a BEM code and a Navier-Stokes actuator disc solver. Results indicate that the center of thrust does not exceed 10% of the rotor radius for the extreme shear case of =0.55. The wake asymmetry tends to increase the out-of-plane bending moment. For the first time, the vertical motion of the wake is described by means of a reactive moment by the rotor on the wake. This has important implications on the fatigue on the rotor’s drive shaft.

Authors:
Kisorthman Vimalakanthan, Gerard Schepers, Wen Zhong Shen, Hamid Rahimi, Daniel Micallef, Carlos Simao Ferreira, Eva Jost, Levin Klein, Thorsten Lutz

Abstract:
As part of the AVATAR and Mexnext projects, this study compares several methods used to derive lifting line variables from CFD simulations of the MEXICO rotor in yawed inflow. The results from six partners within the AVATAR/Mexnext consortium using five different methods of extraction were compared. Overall comparison of the induced velocities at the mid and tip parts of blade shows a good agreement between the tested methods, where the derived angle of attack differs within 1deg. The largest scatter between the methods are located at 210-240deg azimuth (where azimuth=0deg denotes the 12 o’clock position) for the mid-tip parts of blade. For the highly 3D root part of the blade, large differences are observed between the methods.

Authors:
Beatriz Mendez, R. Gutiérrez

Abstract:
Non-conventional vortex generators having cross sections based in thin airfoils are calculated using CFD. The aim is to compare their main characteristics to decide which is the one that adds less drag penalty to the blades.

Authors:
Bastian Dose, Hamid Rahimi, Bernhard Stoevesandt, Joachim Peinke, Jan Gerard Schepers

Abstract:
This work is aimed to investigate the effects of elastic blade deformations on the aerodynamics of large wind turbine rotors subjected to yawed inflow. Due to the  increasing rotor size and advanced light weight blade designs, large blade deflections and significant torsional deformations can be observed on a regular basis for modern wind turbines. However, especially for complex flow situations like a yawed inflow, the role of blade deformations is still not completely understood. In this paper, numerical simulations are conducted on the NREL 5MW and the AVATAR reference wind turbines to gain a better understanding of the involved phenomena. Results are obtained by two numerical methods of different fidelity. First, by the aeroelastic simulation tool FAST, which is based on the low fidelity Blade Element Momentum Theory (BEM) and makes use of common skewed wake correction models. Secondly, by a high-fidelity framework which couples the open-source Computational Fluid Dynamics (CFD) toolbox OpenFOAM with the in-house geometrically non-linear beam solver BeamFOAM. The evaluation of the results is based on the analysis of azimuthal variations of the axial induction factors and sectional forces along the blade span.

Authors:
Imiela Manfred

Abstract:
This paper describes the conduction of CFD simulations for comparison with the experimental data that has been chosen for the third phase of the MexNext-III project. More precisely the results from three different inflow velocities under yawed flow conditions have been analyzed. While the challenge in the case of the small inflow velocity consists in a long simulation time, a small time-step is found to be critical for the simulations in the case of the high inflow velocity. For all simulations torque points out to be the sensitive quantity. Subsequently it can be shown that it is of utmost importance that the post-processing in the CFD simulation is done equivalently as in the experiment. While the relative torque discrepancy for the small inflow velocity is still large due to the small absolute value, the differences in thrust range between 1 and 10%. The best agreement was reached for the case with medium inflow velocity. In this case the thrust between CFD and the experiment match perfectly, while the torque deviation sums up to 9%.

Authors:
Lars Neuhaus, Piyush Singh, Tim Homeyer, Oliver Huxdorf, Johannes Riemenschneider, Jochen Wild, Joachim Peinke, Michael Hölling

Abstract:
Wind turbines are exposed to turbulent wind conditions mainly because of their presence in the atmospheric boundary layer. High and fast velocity changes can be observed under such circumstances. These wind velocity fluctuations lead to local inflow angle fluctuations of several degrees on the blade, which in turn cause load variations on the wind turbine blades. This locally varying inflow can not be handled by a common pitch control system of the whole blade. In order to reduce the effect of local inflow angle fluctuations, especially for large rotor blades a deformable active slat system is presented. With the active slat different aerodynamic coefficients for the same inflow angle can be achieved. For varying inflow angles, the slat can be moved to different positions to reduce the resulting load changes. As the slat system has much less mass than a whole blade, the slat concept allows for a fast reaction on local inflow angle fluctuations. An extensive parametric study is undertaken in order to get a detailed characterization of the slat behavior. The potential of using an active slat for load reduction is demonstrated via synchronized slat deformations and sinusoidal inflow angle variations.

Authors:
Salvatore Maraniello, Rafael Palacios

Abstract:
Internal balancing is used to produce reduced order models of the potential-flow aerodynamics of an horizontal axis wind turbine rotor. The aim is to provide a computationally efficient framework suitable for control synthesis and aeroelastic design of very flexible turbines. The aerodynamics is described through a nondimensional state-space formulation of the unsteady vortex-lattice method. This can resolve 3D forces, requires no kinematics assumption at the lattice degrees-of-freedom and is suitable for linearisation around arbitrary non-zero geometries, in-flow conditions and steady-state loading distributions. Approximate subspace iteration is investigated as a mean to reduce the computational cost of internal balancing. The efficiency of the implementation is assessed for a representative wind turbine rotor geometry.

Authors:
Juan Tang

Abstract:
This paper reports an experimental investigation of the tip clearance effect on the aerodynamic performance of an aerofoil used for the duct of a ducted wind turbine (DWT). The tested two-dimension model is composed of a numerically milled aluminum aerofoil equipped with pressure taps and a uniform porous screen. The experimental setup is based on the assumption that the duct flow is axisymmetric and hence, a two-dimensional setup can be conveniently used to qualitatively analyze the operating principles of a ducted wind turbine. The porous screen, which behaves as an actuator disk without wake rotation, is chosen to have a thrust coefficient similar to the one of a real rotor. Firstly, different gaps between the screen and the aerofoil are tested to point out the influence of this parameter on the DWT performance in terms of aerofoil pressure distribution, aerofoil thrust and flow field features in the rear part of the wing section. Then, the combined effect of tip clearance, of the screen position along the aerofoil chord and of the angle of attack is evaluated through a Design of Experiments (DoE) based approach. By doing so, the role and the significance of these three geometrical parameters on the performance of the aerofoil are highlighted. Initial experiments have been already performed, while the second series of tests will be carried out in January 2018. Hence, a full report of results cannot be provided at present, but it will be incorporated in the full paper and presented at the conference.

Authors:
Ming Zhao, Mingming Zhang, Jianzhong Xu

Abstract:
This paper presents a numerical investigation of the flow physics behind the effects of leading-edge protuberances on the airfoil aerodynamic performance utilizing vortex dynamic method. An improved delayed detached eddy simulation (IDDES) method was adopted and validated through the comparisons with experimental results. Utilizing the IDDES scheme, together with vortex dynamic analysis, investigations were focused on the attached and post-stall regions, respectively. It was found that, within the attached region, the generation and development of the dominant diffused spanwise vortex rings over tubercled airfoil was responsible for the subsequent airfoil performance; within the post-stall region, the impaired flow detachment around both peak and trough sections of tubercles, due to the enhanced momentum injection by the strong streamwise vortices, resulted in better airfoil aerodynamic performance.

Authors:
Janik Kiefer

Abstract:
Empirical data serve as the foundation to computational modeling in the initial stages of the wind turbine design process. In case of aerodynamic simulations, the empirical input is comprised of lift and drag data obtained in quasi two-dimensional wind tunnel tests. In the simulations, the global flow over an entire blade is finally approximated as a spatial summation of the obtained 2-D data, which stands in strong contrast to the true operation of a wind turbine and consequently leads to a higher level of uncertainty. Especially, the near- root region of the blade experiences highly three-dimensional flow conditions, particularly in regions of the blade where the flow separates from the airfoil. This study aims to accentuate the difference between airfoil data obtained in quasi two-dimensional wind tunnel tests compared to airfoil data from a wing with an imposed three-dimensional spanwise pressure gradient. For this, a geometrically altered wing section with a spanwise twist is tested in a wind tunnel and compared to CFD computations.

Authors:
Pan Jia, Ishihara Takeshi

Abstract:
The effects of nonlinear wave on the dynamic responses of Floating Offshore Wind Turbines (FOWTs) in the intermediate water are investigated. Firstly, the predicted dynamic responses of FOWT by the stream function in various wave conditions are validated by the water tank tests. The effects of nonlinear wave on dynamic responses for different wave heights are then examined by comparing maximum velocity and time histories of wave elevation, dynamic responses and mooring tensions predicted by linear and nonlinear wave theories. Finally, the power spectrum densities (PSD) of them are analysed to explain nonlinear wave effects in the high frequency regions.

Authors:
Carlo Rosario Sucameli, Pietro Bortolotti, Alessandro Croce, Carlo Luigi Bottasso

Abstract:
The present work presents a detailed review of wind turbine noise emission models. This study is motivated by the multitude of works addressing the topic of wind turbine noise combined with a severe lack of publicly available experimental data. Both frequency and time-domain formulations are considered in this work, where loading and blade dynamics are computed by a blade-element-momentum aeroelastic model. First, emission spectra generated by some frequency-based models are compared and discrepancies among the models are highlighted, together with some inconsistencies among formulations. Next, a time-domain Ffowcs Williams-Hawkings formulation is investigated with respect to its capability of predicting low frequency noise.

Authors:
Alejandro Gomez Gonzalez, Peder Enevoldsen, Busra Akay, Athanasios Barlas, Andreas Fischer, Helge Aagaard Madsen

Abstract:
An industrial active flap concept for wind turbine rotor blades is validated numerically by means of CFD, as well as experimentally in a wind tunnel environment. This paper presents the numerical and experimental results, as well as a discussion regarding the testing of airfoils equipped with active flaps with a highly loaded aft portion. A conceptual implementation for an offshore wind turbine (SWT-4.0-130) and the potential for load reduction is shown by means of aeroelastic calculations for a reduced design load basis. The work presented herein is conducted within the frame of the Induflap2 project and is partially funded by EUDP

Authors:
Timo Kuehn

Abstract:
This article gives an overview of the results of the wind energy research project AssiSt. Results of the four work packages include flow in complex terrain, wind energy converters (WEC) in complex terrain subject to atmospheric inflow, laminar-turbulent transition, generator cooling, hub aerodynamics, and passive flow control devices. Four different flow solvers (PALM, FLOWer, THETA, OpenFOAM) are in use during the course of the project depending on the corresponding problem requiring a specific solver problem affiliation. Key achievements of the project are the coupling of atmospheric LES (PALM) and URANS simulations of the complete WEC (FLOWer as well as THETA) in order to imprint the external turbulent flow fields to the inflow of the WEC for physics resolved load simulations, numeric replication of complex flows over wing vortex generator with OpenFOAM and efficiency augmented pressure loss simulations on very complex industrial geometries of ENERCON’s direct drive WEC generators for precise cooling analyses. As industrial validity of all methods, model and process developments were key objectives of this research project.

Authors:
Lorenzo Battisti, Alessandra Brighenti, Marco Raciti Castelli, Giacomo Persico, Vincenzo Dossena

Abstract:
Performance and wake measurements on a H-Darrieus vertical axis wind turbine are discussed on the basis of an extensive experimental campaign performed at the large scale, high speed wind tunnel of the Politecnico di Milano (IT). The aerodynamic torque is presented as a function of the azimuthal angle of revolution, while the velocity field in the wake is fully characterized by means of a point to point detailed measurement on the midspan plane, where the influence of both support struts and tip vortices are negligible.Particular care is taken in the description of the experimental setup as well as in the presentation of the measurements and consequently the here proposed achievements can be considered as a benchmark for the validation of numerical models.

Authors:
Ricardo Pereira

Abstract:
This article describes a probabilistic approach to design airfoils for wind energy applications. An analytical expression for the probability of perturbations to the operational blade-section angle of attack is derived, including the combined influence of wind shear, yaw-misalignment and turbulence intensity. The theoretical angle of attack fluctuations are validated against a aero-structural  simulation of a 10 MW horizontal axis wind turbine, operating under different inflow conditions. Finally the probabilistic approach is incorporated into a multi-objective airfoil optimizer and solved with a genetic algorithm. Results illustrate the compromise of maximizing airfoil performance for a specific angle of attack versus airfoil  performance robustness over a large range of angle of attack fluctuations.

Authors:
Bruce LeBlanc, Carlos Simao Ferreira

Abstract:
Large floating offshore wind turbines are beginning to show promise as a technology with several pilot projects being completed in recent years with more on the near horizon. Due to the complexities of the floating configuration there are substantial costs associated with the platform and mooring systems for these types of deep water machines. The vertical axis wind turbine has been proposed as a potential solution for lowering the overall costs of turbine installations. This is achieved through a lower center of gravity and a greater tolerance to platform motions than an equivalent horizontal axis machine. The cost of the platform system is related to the overturn moment of the turbine in crucial operational states. The largest contribution to this moment is the rotor thrust. In this work, an experimental wind tunnel model has been made to study the loading of a 2-bladed H-type VAWT. The model is capable of individual active pitch control and is equipped with sensors to measure thrust and side loading with respect to the turbine. This paper introduces the experimental wind tunnel model referred to as PitchVAWT, discusses the method of determining rotor thrust and side loads, and presents measured results for a fixed pitch case with varying tip speed ratio. The data presented will be made available for further evaluation and potential validation of turbine numerical codes.

Authors:
Christian Bak

Abstract:
Vortex generators have in recent years been used extensively on pitch regulated wind turbines. A new trend has been to use vortex generators on thinner airfoils on the outer part of the blades. However, not much data is available for thin airfoils with vortex generators. That is the reason to carry out wind tunnel tests on a NACA 63-418 airfoil with 18% relative thickness in the Stuttgart Laminar Wind Tunnel. The airfoil was tested in clean condition, but also with different heights of leading edge roughness and vortex generators and different positions of the vortex generators. Results of the airfoil performance in terms of polars, maximum lift and lift-drag ratio are shown with focus on how the vortex generators influence the performance of the airfoil.

20 June  |  21 June  |  22 June  |  Events View
AA | CM | DSE | MET | MST | WWT

Go to Top