Tuesday, 27 September 2016
17:00 - 18:30 Innovative rotor design
Turbine technology  
          

In the conversion of wind power, the rotor is the first point of energy transformation, transforming the kinetic energy of the wind into torque and rotation. Rotor technology sets a limit of the energy converted and the loading required to convert this energy. The load cycles are design drivers, influencing the mass and operation of the rotor, and therefore the entire turbine. In addition to extracting kinetic energy from the flow, the rotor creates a pressure field that generates the wake and leads to noise generation. Rotor design optimisation must therefore account for power and load optimisation, constrained by the full lifecycle, fatigue life and noise, among other boundary conditions. This session focus on innovations in both rotor design methodologies and components.

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Learning objectives

• Understand the effect of geometric non-linearities in the fatigue life of the blade;
• Evaluate the possible impact of flexible certification guidelines in rotor design optimisation;
• Analyse the application of trailing edge serrations as a noise reduction device;
• Evaluate the potential of active flap control for both alleviation and power optimisation;
• Evaluate the impact of integrating the turbine lifecycle in the design optimisation of rotors.

This session will be chaired by:

Ashish Singh LM Wind Power, India
Co-authors:
Ashish Singh (1) ^F Jose Mathew (2) Jesper Madsen (3) Carlos Arce (4)
(1) LM Wind Power, Bangalore, India (2) LM Wind Power, Bangalore, India (3) LM Wind Power, Kolding, Denmark (4) LM Wind Power, Kolding, Denmark

Product insertion of LM Wind Power serrations

Introduction

Accelerated growth of wind energy will lead to four times more wind turbines being installed in the next ten years as compared to today’s total installed turbines. The ability to design low-noise wind turbine blades will have a large impact on the wind energy market as many of the future wind turbines will be placed onshore close to urban areas where noise emission regulations are restrictive. Reduction of aerodynamic noise generated by the wind turbine blade will allow for more wind turbines to be situated onshore, thus allowing a larger installed capacity and would enable wind turbines to run with increased tip speed. The reduction of wind turbine noise implies that the blades can rotate faster for a given diameter or for a given rotational speed, longer blades can be designed. In both cases, annual energy yield will increase, leading to a reduction in overall cost of energy.

Approach

Retro fitting serrations onto the trailing edge of wind turbine rotor is an accepted method of achieving reduction of aerodynamically generated noise in the field. Evidence from literature suggests that serrations can indeed reduce the noise generated by the turbulent boundary layer on the trailing edge of the airfoil, which is a primary component of the aerodynamically generated noise. Although the physics of serration noise reduction is still an area of active research, the performance of serrations has been proved both in anechoic wind tunnels as well as in the field. LM Wind Power has adopted serrations for enabling noise reduction and over the past 8 years has built a large database of learnings related to design, modeling, testing, manufacturing and field validation of serration designs.

Main body of abstract

This paper provides a summary of efforts undertaken by LM to successfully translate serration designs from paper to a viable commercial product. Although literature review on serrations shows several designs that are suitable for wind turbine noise reduction, the challenge lies in addressing the underlying issues that would ensure the structural reliability of the designs in addition to guaranteeing consistent noise reduction. Reduced order models were generated for predicting the aerodynamic, acoustic and structural performance of the serrations. Detailed experiments were conducted in aerodynamic wind tunnel to study the impact of serrations on the aerodynamic performance of airfoils. Aerodynamic loads on the serrations were measured using strain gauges attached to the serrations for a range of operating conditions. These were followed by tests in anechoic wind tunnels where the noise reduction performance of serrations was measured. Detailed static and fatigue tests of various serration designs were conducted to understand the impact on structural integrity. Various methods for attaching the serration on the rotor were experimented with to ensure long life of serrations in the field. These were followed by multiple field validation campaigns where the acoustic performance of serrations attached to wind turbine rotors was measured.

Conclusion

LM has successfully addressed the challenges associated with serration aerodynamic and acoustic performance, structural integrity, manufacturing, material and installation. Current serrations developed by LM provide a noise reduction of at least 1. 5 dB in the field on turbines with diameters in the range 80 m – 120 m and 2- 3MW capacity. Product insertion has been successfully completed on multiple customer turbines and LM is on the lookout for processes and techniques to reduce the uncertainty associated with the field performance of the serrations


Learning objectives
The primary focus of this paper is to list the challenges involved in converting serration designs to reliable products that can be installed on wind turbine blades in the field. Summary of how LM addressed each challenge will be described briefly, including key results from test and validation campaigns.