Simulations Key to More Efficient Wind Farms

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How can a wind-turbine OEM as well as their countless suppliers squeeze more power from the wind using already well developed equipment?

Even a small efficiency increase would be welcome. The viability of the business depends on it.

The wind business is also counting on such gains to improve returns on investment, especially in times of economic uncertainly and the heighten demand for green energy.

The industry relies on technical developments to drive innovation, minimize cost, and harness wind energy at efficient and reliable levels unimaginable a few years ago. For example, consider an installation of large offshore wind turbines and more recently in floating configurations. It is a technological achievement for energy companies to design, install, and efficiently operate a super structure with blades that could span a football field and tolerate wave and wind loading at different angles of attack.

Engineering simulation software is playing an increasingly critical role in development and capture of new information about the detailed workings of a variety of wind-turbine designs and under varying loads. Engineering simulations in 3D with science-based software compliments conventional physical testing and prototyping. Engineering simulation methods solve the fundamental mathematical equations related to structural mechanics, fluid mechanics, thermal, vibration, electromagnetics, and acoustics. These allow interactionbetween different physics in multiphysics simulations.

Such software is developed to the point where it is possible to, for example, simulate blade efficiency and related aerodynamic structural loads from a range of winds, including start up conditions, different wind speeds, directions, and gusts, and then perform cooling analysis on electronic and moving components all in the same simulation environment.

This is of special interest in the wind industry because turbines often include all aspects of fluids, structural, and electrical design. The programs are relatively easy to use, while the underlying technology is comprehensive and often well validated.

The simulation software tools in general are applied to a broad range of applications covering many aspects of aerospace, mechanical, civil, electrical and chemical engineering disciplines. The software is already assisting wind engineers as they develop different sized turbines and to squeeze out even small efficiency gains. Engineers in wind energy and those at companies in their supply chains apply computational methods to a range of applications, including:

• Aerodynamic design. This software allows considering thrust coefficients, structural integrity of blades, ultimate loads and fatigue, noise predictions, fluid structure interactions from wind gusts, bird strikes, icing, boundary layer transitions, and near wake and far field studies.

• Electromechanical-system simulations include electrical machines, variable-speed controls, transformers, power electronics, power distribution, and sensor and actuator design.

• Site selection and farm layout involves maximum project power output: peak and average, wind loads, fatigue, and logistics.

• Turbine placement work considers variable terrain, roughness, forestry, multiple wake effects, along with buildings and setbacks.

• Component design includes examining blades, gearboxes and bearings, generators, nacelles, rotors, yaw drives, and motors.

• Structural design work examines towers and rotors for their structural integrity, safety, power-conversion efficiency, installation costs, maintenance, and offshore transport.

Other examples include two well known design concerns for wind-turbine engineers: overheating and material stress. Engineers can take advantage of the insight provided by advanced and high-fidelity solutions.

A growing application for engineering simulation deals with the location or siting of wind farms, on and offshore. One critical aspects in development of offshore wind energy lies with the substructures and the interaction between them and the sea floor. Furthermore, it is becoming more evident that the losses from wakes and effect of complex terrains can be significant. This may even be true for offshore installations even though the “terrain” is quite benign.

Accompanying screen shots show sample results from a computational fluid mechanics study of the on-shore Black Law Scotland wind farm. Its 54 wind turbines have a total power capacity of 125 MW with a relatively small height variation (170m) across the farm. The study was to look at the effect of wind velocity and direction while taking into account effects of wake and vegetation, along with turbine operations and downstream effects. A business objective was to determine overall viability of the site. The simulation was performed for different wind velocities from different directions. The images show it is possible to attain a detailed map of, in this case, normalized velocity behind the rows of turbine blades for wind entering the area from the lower left. The benefit of the simulation is that it is possible to study turbine placement, their relative arrangements, along with vegetation, surface roughness, and other local geometric effects. For instance, the image on the left shows only the turbines and associated wind-wake effects for the arrangement. Wind velocities between the turbine arrangement are relatively uniform and show narrow wake effect downstream. The image on the right uses the same arrangement and wind velocity with additional upstream disturbances caused by a forest canopy. The resulting velocities in between turbines and downstream effects are markedly lower. This indicates the influence of the terrain and forest and a potential output loss for this arrangement.

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