Smart Rotor

1. Smart Rotor 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. • Background • 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. • 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. Model Validation against SNL rotor Aerospace Engineering 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 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 Load reduction ability with smart rotors Current and Future work 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 non-linear 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 9-11 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