GE using Large Eddy Simulation on Sandia’s Red Mesa to lay groundwork for quieter wind turbine blades with better power yield
|Transition of flow to turbulence on a wind-turbine airfoil; isosurfaces of vorticity from a Large Eddy Simulation (LES). Credit: GE Global Research. Click to enlarge.|
GE Global Research, the technology development arm of the General Electric Company, recently completed a research project in partnership with Sandia National Laboratories that could significantly affect the design—and thus the noise and power output—of future wind turbine blades.
A 1 decibel quieter rotor design would result in a 2% increase in annual energy yield per turbine. With approximately 240 GW of new wind installations forecasted globally over the next five years, a 2% increase would create 5 GW of additional wind power capacity—enough to power every household in New York City, Boston, and Los Angeles, combined, GE Research noted.
In a 2011 survey of techniques to reduce wind turbine blade noise, Sandia researcher Matthew Barone noted that:
There are two primary classes of noise sources on a wind turbine. These include mechanical noise due to vibrations in the drive train and gear noise, and aeroacoustic noise due to unsteady aerodynamic processes on the rotor. Mechanical noise, while it can potentially be a large contributor to overall wind turbine noise, is usually relatively straightforward to reduce using techniques to dampen or isolate mechanical vibrations in the nacelle, or by employing sound absorbing material. Aeroacoustic noise is more difficult to mitigate, and is the dominant noise source on modern wind turbines.
Aeroacoustic noise sources on a wind turbine can be divided into two main classes: airfoil self-noise, due to interaction of a nominally steady ﬂow with the blades, and turbulent inﬂow noise, due to scattering of turbulent wind fluctuations by the blades. Airfoil self-noise is further divided into various noise mechanisms; the two most relevant mechanisms are turbulent boundary layer-trailing edge noise (or, “trailing edge noise”), and blade tip vortex noise. Early models of wind turbine noise tended to address each of these possible noise sources and, up until very recently, it was difficult to assign prominence of one aeroacoustic noise source over the others. It has been known for some time that blade tip speed is limited by aeroacoustic noise, and trial-and-error design approaches have focused on tip shapes that resulted in relatively low noise.
|Noise generation due to turbulent flow over the trailing edge of a wind-turbine airfoil; dilatation contours from a Large Eddy Simulation (LES) are shown in the background. (Courtesy: Prof. Lele, Stanford University). Click to enlarge.|
GE’s testing involved Sandia’s Red Mesa supercomputer running a high-fidelity Large Eddy Simulation (LES) code, developed at Stanford University, to predict the detailed fluid dynamic phenomena and resulting wind blade noise.
For a period of three months, this LES simulation of the turbulent air flow past a wind blade section was continuously performed on the Red Mesa HPC. The resulting flow-field predictions yielded valuable insights that were used to assess current engineering design models, the assumptions they make that most impact noise predictions, and the accuracy and reliability of model choices.
We found that high fidelity models can play a key role in accurately predicting trailing edge noise. We believe that the results achieved from our simulations would, at the very least, lay the groundwork for improved noise design models.—Mark Jonkhof, Wind Technology Platform Leader at GE Global Research.
To ensure that GE’s wind blades do not pose noise issues today, airfoil level acoustic measurements are performed in wind tunnels, field measurements are done to validate acceptable noise levels, and noise-reducing operating modes are implemented in the control system. Better modeling will help maintain the current low noise levels while boosting output.
Sandia and other DOE national laboratories are using high-performance computing resources to tackle complex design problems in wind energy, such as reducing turbine blade noise to achieve significant reductions in cost-of-energy. Sandia helped GE gain valuable insights into blade noise mechanisms and how design engineers can improve their models.—Matt Barone, of Sandia’s Aerosciences Department, formerly of the Wind Energy Technologies Department
Red Mesa. In 1997, Sandia’s ASCI Red architecture was first worldwide to break one teraflop, or a trillion operations per second. In 2004, in partnership with Cray Inc., Sandia developed the Red Storm platform, which grew into a commercial success for Cray and evolved into the Red Sky and Red Mesa supercomputers.
Matthew F. Barone (2011) Survey of Techniques for Reduction of Wind Turbine Blade Trailing Edge Noise. (SAND2011-5252)