Smart Rotor
Background
Aerospace Engineering
During the last decade research on the field of smart
rotor has advanced significantly. Fundamental
aerodynamics, structural and control concepts have
been established and simulators created for
distributed aps on wind turbine blades, which are
considered the most promising option. Also a proof of
concept has been done under laboratory conditions.
However, the results obtained under these conditions
can only be partially transfer to the real application
as the control authority of smart rotors is limited
compared to full pitch control. The steps that need to
be taken before smart rotors can be successfully
exploited are in the design of reliable systems that
can operate under environmental conditions without
inspections. Besides that, other potential advantages
of distributed control need to be established such as
the effect on other components of a wind turbine for
example the gear box or the power system. Finally, it
is necessary to investigate what benefits can be
achieved if blades are designed with distributed
control right from the start instead of applying
control schemes to already existing turbines.
PhD Candidate: Lars Oliver Bernhammer
Department: AWEP
Section: Wind Energy / Aerospace Structures
Supervisor: R. De Breuker
Promoter: G.A.M. van Kuik
Start date: 1.9.2011
Funding: Far and Large Offshore Windturbines
Cooperations: XEMC Darwind, Sandia National Labs, Technion
None of these systems is developed to a level that
makes it usable for offshore turbines. The electric
motors are built of many parts, which makes them
maintenance sensitive. The pressurized flaps and the
shape memory alloy driven trailing edge devices have
strong limitations of the frequency bandwidth.
A wide range of actuation devices has been
considered. Among these are:
• Trailing edge flaps
• Microtabs
• Bending-torsion coupling
• Variable camber
• Suction/Blowing
• Plasma actuators
• Slats and other leading edge devices
Research has converged to trailing edge flaps
because of their control authority and bandwidth.
Model Validation against SNL rotor
Progress
The progress can mainly be found when looking at
the simulation targets set. An aeroservoelastic code
has been created based on a evaluation from a
steady BEM based code. The new code includes
unsteady aerodynamics, a dynamic inflow model and
a more detailed structural model. This code has been
verified
numerically
against
simulations
of
commercial software such as GH Bladed and FAST.
Validation of the code compared to a full scale Smart
Rotor experiment also has been done. Based on the
model linearization a controller has been created to
simulate the reduction of the root bending mode for
the given Smart rotor.
Deformable trailing edge concepts
Challenges, Opportunities and Design Options
So far no trailing edge flap design can fulfill all the
requirements of a smart rotor. Performance criteria
are
• Actuation bandwidth from 0-6 Hz
• 12 degree tab deflection
• Smooth transition between deformation
states
Besides that environmental conditions have a strong
impact on the trailing edge design. One should
consider
• Shielding from oxidation
• Shielding from lightning strikes
A range of actuation mechanisms have been
proposed
and
demonstrated
in
laboratory
environment. Among these are:
• Electric motors (Sandia)
• Servo-electric motors (University of
Bristol)
• Pressurized rubber flaps (DTU)
• Shape memory alloys (TU Delft)
Sandia National Lab Rotor
Project Objectives
Simulation
Load reduction ability with smart rotors
Current and Future work
• Create aeroservoelastic analysis environment
• Determine contribution to fatigue load reduction
and cost of energy
• Demonstrate individual flap control numerically
Integration
• Verify numerical tool
• Demonstrate scalability of smart blades to full size
turbine configurations
• Implement numerically obtained controllers into
real model
Currently the structural model is being improved. A
new approach has been formulated based on a
corrotational framework using piecewise linear
approximations of the structure obtained by modal
deformations. This approach is verified against nonlinear simulations of full finite element models. In a
final step in the simulator development this model
will be integrated into the aeroservoelastic code.
Starting in summer, the detailed section design will
be addressed. By the end of this year, a working
design should be available and can be tested 2014.
Conferences publications
Bernhammer, L.O., De Breuker, R., Karpel, M., “Active Rudder Flutter Suppression using Distributed Flaps actuated by Piezoelectric Tabs”, 22nd International Conference on Adaptive Structures and
Technologies, October 10-12 2011, Corfu Greece
Bernhammer, L.O., van Kuik, G.A.M., De Breuker, R., “Delft University Smart Wind Turbine Aeroelastic Tool (DU_SWAT): A New Aeroservoelastic Horizontal Axis Wind Turbine Analysis Tool”, Proceedings of
8th PhD Seminar on Wind Energy in Europe, September 12-14, 2012, ETH Zurich Switzerland
Bernhammer, L.O., van Kuik, G.A.M., De Breuker, R., “How far is smart rotor research and what steps need to be taken to build a full-scale prototype?”, The Science of Making Torque from Wind, October 911 2012, Oldenburg, Germany
Bernhammer, L.O., Teeuwen, S.P.W., De Breuker, R., van der Veen, G.J., van Solingen, E. , “Performance Optimization and Gust Load Alleviation of a UAV Wing Using Variable Camber”, 23nd International
Conference on Adaptive Structures and Technologies, October 11-13 2012, Nanjing, China
Bernhammer, L.O., De Breuker, R., van Kuik, G.A.M., van Wingeredn, J.-W., Berg, J., “Model Validation and Simulated Fatigue Load Alleviation of SNL Smart Rotor Experiment”, 51st AIAA Annual Science
Meeting, January 2013,Grapevine, USA
Journal publications
Bernhammer, L.O., De Breuker, R., Karpel, M., van der Veen, G.J., “Aeroelastic Control Using Distributed Floating Flaps Activated by Piezoelectic Tabs”, Journal of Aircraft, Pre-print March 2013
Bernhammer, L.O., Teeuwen, S.P.W., De Breuker, R., van der Veen, G.J., van Solingen, E. , “Performance Optimization and Gust Load Alleviation of a UAV Wing Using Variable Camber”, Submitted to Journal of
Intelligent Materials Systems and Structures