idsession
codetitle

Invited-1

A-1-1

European R&D cooperation in windpower technology

Dr. Peter Hauge Madsen

Department of Wind Energy, theTechnical University of Denmark

77

A-1-2

3D analysis of a straight-bladedvertical axis wind turbine by panel
methodMs. Alisa Nakai

Mie University

114

A-1-3

Evaluation of wind turbine wakesimulation focusing on gridresolution

Mr. Keita Kimura

The University of Tokyo

13A-1-4Wind-powered Thermal Energy
System (WTES), which employs
direct thermal conversion andthermal energy storage

Dr. Toru Okazaki

The Institute of Applied Energy

Invited-2

A-1-5

Advanced aerodynamic rotor control
options: Flaps, Plasma's and modern Prof. Gerard J.W. van Bussel
stall control

Delft University of Technology

88

A-1-6

Aerodynamic Loads of Horizontal
Axis Wind Turbines in Realistic
Operational Conditions and Loads
Mitigation Using Individual PitchControls

Dr. Yasutada Tanabe

Japan Aerospace Exploration
Agency170

A-1-7

Detailed wind inflow measurements
using a nine-beam nacelle lidar

Dr. Hirokazu Kawabata

Advanced industrial science andtechnology

Presenter nameAffiliation

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31-Oct. 13:30 - 15:45 [ Innovative onshore wind technology／Wind Turbine Technology (1) ][Invited Speaker]

European R&D cooperation in wind energyPeter Hauge Madsen
Head of Department of Wind Energy, The Technical University of Denmark

Abstract:
Cooperation on R&D in wind energy between research institutes and universities and alignment of the research in theindividual member states with the European Union’s framework programme, p.t. Horizon2020, is a key element of theEU SET-plan, which aims to overcome Europe’s climate and energy challenges. In rder to provide strategic researchleadership, coordination and alignment the major research organisations in Europe formed the European Energy Research
Alliance (EERA) some years ago. The Joint Programme for Wind Energy (JPWind) was among the first 4 joint
programmes and has now functioned for five years. In parallel the European Commission has supported the formation ofTechnology Platforms, which has been industry led and acted as a platform for discussions between industry andacademia and joint priorization of R&D needs. In September 2016 the European Technology and Innovation Platform forWind Energy (ETIPWind) presented its latest Strategic Research and Innovation Agenda with contributions from EERA
JPWind. The presentation will focus on the organization and joint programming of European wind energy research inEERA JPWind, and present the strategic research recommendations of the industry and academia in ETIPWind.Thepresentation will conclude with some key results from the larger research initiatives of the EERA Joint Program for Wind
Energy, namely the DTOC and the Innwind projects. The results demonstrate how cooperation in wind energy R&D canlead to design & analysis tools as well as innovations well above the limitations of the individual research groups.

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31-Oct. 13:30 - 15:45 [ Innovative onshore wind technology／Wind Turbine Technology (1) ]3D analysis of a straight-bladed vertical axis wind turbine
by panel method
Alisa Nakai, Takao Maeda, Yasunari Kamada, Junsuke Murata, Masayuki Yamamoto,
Tatsuhiko Ogasawara, Kento Shimizu and Takuji Kasuya
Mie University

Abstract:
Vertical Axis Wind Turbines (VAWTs) have an axis of rotation which is normal to inflow wind. Because the power output ofVAWTs independent of the direction of the wind, they don’t require any yaw mechanisms. In addition, straight-bladed verticalaxis wind turbines which have uniform blades, without taper and without twist, suit mass-production because of the simplestructure. Therefore, VAWTs have a possibility of lower manufacturing cost than that of Horizontal Axis Wind Turbines(HAWTs). Additionally, total gravity center of VAWTs are lower because generators of VAWTs can be placed near groundresulting in higher stability. It can be said that VAWTs have a potential of applying as urban-type wind turbines.
Even though much effort on research of VAWTs has been made, the understandings of effects of the complex flow fields
aren’t enough to design low-cost and highly-efficient VAWTs.
Important factors which make the problem difficult are unsteadiness of relative inflow to blades and 3-dimensionality offlow filed. Magnitude and direction of relative inflow to the blades vary with azimuth angle. Especially in downstream half ofthe rotor, the blade pass through the flow field disturbed by upstream blades. It brings about periodic aerodynamic load
fluctuation. Finite length blades generate tip vortices which form 3-dimensional induced velocity field around the rotor.
The purpose of this study is clarification of 3-dimensional effects on aerodynamic force fluctuation of straight-bladed
VAWT rotor. For the purpose, panel method based on lifting line theory is used. In this method, rotor blades and wake arerepresented by vortex panels. Aerodynamic force on rotor blades are determined by Neumann condition at the blade surface
considering the induced velocity from other rotor blades and wake calculated by Biot-Savart law. The method has advantages
that it is capable of calculation for unsteady and 3-dimensional flow fields and the computational cost is lower than that ofcomputational fluid dynamics (CFD).
In this study, aerodynamic performance and load fluctuation on straight-bladed VAWTs are calculated by the method. The
calculation results are compared to wind experimental results observed in a wind tunnel. In the wind tunnel experiment,pressure distributions on rotor blade section at different span positions are measured.
The calculation results show qualitative agreement with the experimental results. Sectional aerodynamic force is largest at
the middle of blade span and decreases with approach to the tips. This paper shows the effects of 3-dimesional flow field on
aerodynamic force on straight-bladed VAWTs.

Evaluation of wind turbine wake simulation focusing on grid resolution
Keita Kimura1, Yasutada Tanabe2, Takashi Aoyama1, Makoto Iida1,Yuichi Matsuo2 and Chuichi Arakawa1
1The University of Tokyo, 2Japan Aerospace Exploration Agency(JAXA)

Abstract:
Numerical analysis is less expensive than an experimental setup and it readily provides field data such as velocity andvorticity. However, to simulate the entire structure of a wind turbine wake, a large number of grid points is needed. In thisstudy, The influence of the grid resolution on wake characteristics is studied by changing the number of grid points of the wakeregion. Such information can be useful to reduce the costs of the CFD simulation of wind turbines.
In this paper, a CFD analysis is performed by using rFlow3D, which was developed by the Japanese Aerospace eXploration
Agency (JAXA). Note that rFlow3D can handle moving overlapped structured grids and can accurately simulate rotating
blades. In wake region, high-resolution grid is set to capture the complex wake structure such as tip vortices. By changing theresolutions of grid, the effects on wake characteristics such as velocity recovery and vorticity are investigated.
According to the results obtained by the CFD, values do not significantly change as for overall wake characteristics. Despitelarge changes in the grid resolution, velocity recovery and/or vortex breakdown process indicate similar tendency. On the other
hand, the microscopic values such as the maximum vorticity and core radius of the tip vortices were found to be susceptible tochanges in the grid resolution. As the grid resolution decreased, the vorticity decreased and the initial core radius increased.
However, the vorticity decrement rate was the same for the medium and coarse grids. These results suggest that if a coarse grid
does not capture several microscopic values, the overall advection process is reasonably simulated. That means grid resolution
for wind turbine simulation can be classified according to the focusing scale. (For instance, a coarse level can simulate
macroscopic advection of the vortices. Meanwhile, a fine level can capture the maximum and minimum values of vortices)
In the presentation, the results of additional cases will be shown. In addition, the relationship between the computational
domain of high resolution grid and recovery process will be discussed.

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31-Oct. 13:30 - 15:45 [ Innovative onshore wind technology／Wind Turbine Technology (1) ]Wind-powered Thermal Energy System (WTES),
which employs direct thermal conversion and thermal energy storage
Toru Okazaki, Hiroshi Hasuike, Kenji Watanabe and Taro Kawamura
The Institute of Applied Energy

Abstract:
Wind-powered Thermal Energy System (WTES) is the novel simple idea to realize the economic base load power source.
Present wind power is intermittent and cannot be operate without the back-up fossil fuel thermals. WTES is proposed toovercome this issue. The thermal energy is generated from the rotating energy directly at the top of the tower by the heatgenerator, which is very light and robust electric brake. The rest of the system is the same as the tower type concentrated solar
power (CSP).
The advantages of WTES are: 1) economical direct drive system, 2) reliable heat transfer system, 3) very economical thermalenergy storage, 4) very high capacity factor of transmission line, 5) dense deployment of wind towers in wind farm, 6) fullharvesting of the wind energy at the tower. The advantage No.1 is realized by the light and robust heat generator, which is theeddy current brake. No.2 & 3 are proved in CSPs. The energy storage cost by thermal condition is only 1/20 to 1/100 of thebatteries. No.4, 5 and 6 are realized by the thermal storage. The power output has no direct connection with the wind condition.
No.5 is also realized by the robust direct drive.
The disadvantage is the employment of inefficient thermal machine, of which efficiency is half of the batteries. This wellknown fact blocked the study of WTES until recently. The quantitative research from the viewpoint of total electric powersystem reveals that the economic efficiency of WTES is much better than that of the conventional wind power stabilized by theboth back-up thermals and batteries. This quantitative research of energy cost is reported in this study.

4/631-Oct. 13:30 - 15:45 [ Innovative onshore wind technology／Wind Turbine Technology (1) ][Invited Speaker]

Advanced aerodynamic rotor control options:
Flaps, Plasma's and modern stall control
Gerard J.W. van Bussel and Ricardo PereiraWind Energy Group, Faculty of Aerospace Engineering, TU Delft

Abstract:
The paper presents the result of a study on an alternative horizontal axis wind turbine rotor concept in which modern
active stall control (ASC) is adopted.
In this concept the power control of the wind turbine is achieved in a combination of rotor speed control and activeflow control actuators. These two control modes are used to fine tune the aerodynamic blade loads across the complete
operational envelope.
In the operational range from cut-in to close to the nominal wind speed, the wind turbine is operating just as an
ordinary modern pitch controlled rotor. But above the nominal speed, the rotor speed is kept constant and active flow
devices are applied to control loads around rated power and above.
It will be shown that, out of several active flow control devices such as trailing edge jets, smart trailing edge flaps andplasma actuators, on the plasma actuators applied on selected locations on the suction side of the rotor blade, can provide
sufficient control authority to control the loads in a satisfying fashion.
Out of the several plasma actuation possibilities the Alternating Current Dielectric Barrier Discharge (AC-DBD)
plasma actuator, characterised by a.o. the absence of moving parts, negligible mass and virtually unlimited bandwidth ofactuation came out as the best implementation.
An extensive study was performed at TU Delft on the performance of such actuators. This is not part of the current
presentation, but its results are used to design a series of AC-DBD actuated airfoils for implementation into ASC rotor
blades witch will be presented.
A final rotor planform design for a 5MW rotor will be presented as well and it includes the planform geometry design,
rated rotational speed, spanwise laminate skin thickness as well as the dedicated AC-DBD plasma actuated airfoils(“WAP” airfoils) with the actuation scheduling,
Results show that, compared to variable-pitch rotor blades, the ASC planform displays increased chord at inboard
stations with decreased twist angle towards the tip, resulting in increased AOA. Actuation is employed to trim the loads
across the operational wind speed envelope and hence results in a significant reduction of load overshoots.

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31-Oct. 13:30 - 15:45 [ Innovative onshore wind technology／Wind Turbine Technology (1) ]Aerodynamic Loads of Horizontal Axis Wind Turbines in Realistic
Operational Conditions and Loads Mitigation
Using Individual Pitch Controls
Yasutada Tanabe1, Takashi Aoyama1, Harutaka Oe2, Makoto Yamamoto2,Makoto Iida3 and Chuichi Arakawa3
1Japan Aerospace Exploration Agency, 2Tokyo University of Sciences, 3The University of Tokyo

Abstract:
Aerodynamic load of horizontal axis wind turbine (HAWT) operated in realistic complex conditions such as yawed wind andatmospheric boundary layer (ABL) wind profile are studied. Individual pitch control (IPC) technique is applied for the load
mitigation especially for the HAWT operated in ABL inflows. Larger wind turbines are under development to pursue greater
efficiency. More challenges exist in the design of the larger wind turbines where higher reliability and endurability are required
especially in Japan where severe gusts and typhoons frequently visit. Understanding of the aerodynamic loads in more realistic
operational conditions is the start point. A CFD code, rFlow3D, developed in JAXA especially for the applications to rotorcraftis extended for simulating the HAWTs operations. It was validated with the NREL Phase VI and MEXICO wind turbine
experimental databases. It is found that in yawed wind, the variations of the aerodynamic loads increases with the increase ofyaw angle. The load variations in the ABL inflow condition are significantly high. An individual pitch control system to reduce
the yawing and tilting moments of the wind turbine in ABL is constructed and a trim routine is numerically simulated and theeffectiveness is validated based on a three-bladed and a two-bladed horizontal axis wind turbine. It is found that the averages ofyawing and tilting moment on the rotor hub can be reduced nearly to zero through the 1/rev cyclic controls. Furthermore, thefluctuations of the moments on the hub of a two-bladed wind turbine can be significantly reduced simultaneously through the1/rev cyclic control. The oscillations of the flapwise bending moments on blade root can be remarkably reduced although theaverages are not influenced while the influence of IPC on the power generation is minimal.

Detailed wind inflow measurements using a nine-beam nacelle lidar
Hirokazu Kawabata, Yoshihiro Kikushima and Tetsuya Kogaki
Advanced industrial science and technology

Abstract:
This study reports on wind inflow measurements performed using a nine-beam nacelle lidar. Various nacelle lidar systems
have been used for the measurements of wind inflow to realize high-performance wind tur-bines. The measurement of a twobeam nacelle lidar used as a simple measurement system has been compared with those of a nacelle anemometer and a metmast. The 10-min-averaged data obtained from the two-beam nacelle lidar have good measurement accuracy, but the lidar isunable to measure wind shear. Monitoring of wind inflow for multi-megawatt wind turbines requires an advanced lidar systemthat can measure wind shear. Further, there is a lack of observation reports on measurements using the two-beam nacelle lidar
under strong turbulence conditions. In this study, the authors evaluated the measurement characteristics of a nine-beam nacellelidar installed on a 300-kW wind turbine. This nacelle lidar could measure radial wind speeds in nine directions; further,horizontal wind speeds were calculated using a three-beam system. The use of three beams led to a considerably higher
availability of the lidar in comparison to the availability when using two beams. This lidar also could measure wind speed
uniformity in a transverse direction by using three beams. The measurements of this study revealed that 10-min-averaged data
could confirm wind uniformity, but instantaneous data could not confirm wind uniformity under a strong turbulence condition.
To discriminate the lidar measurement data in terms of their quality, some filtering indexes for these data were proposed.
Continuous and reliable monitoring of wind shear could be achieved by filtering the measured data. The nine-beam nacelle lidar
was also used for the detection of strong turbulence. Because of the high data availability, the lidar could measure strong
turbulence information for feedforward control.

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