Wind Turbine

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wind energy Mapping a <strong>Wind</strong> Farm by Joseph K.W. Lam, Fluent Europe A typical wind map, and close-up showing the locations of the turbines Awind farm is a plot of land where a number of wind turbines operate concurrently. The power delivered by the wind to a turbine is proportional to the swept area of the rotor blades and the wind speed cubed. <strong>Wind</strong> turbines start to generate electricity at wind speeds of about 10 mph, and reach their maximum or rated power output at about 33 mph. Depending on the location, a wind farm will produce electricity for about 80-85% of the time, mostly at low wind speeds. The site of the farm, in particular the topology of the land at and surrounding the farm, can play a significant role in the efficiency of the collective energy output of the turbines. At Renewable Energy Systems in the UK, FLUENT has been used to predict the wind speeds for an existing wind farm at Coal Clough, Lancashire. There are 24 turbines at Coal Clough providing about 6,000 homes with their electricity needs. The analysis was done to generate a “wind map”, or high resolution contour map of wind speeds at a certain height above the ground. The best wind maps take into account the variations in the local terrain, including the topography of the land and the presence of nearby structures. A substantial amount of measured wind speed data was available, and was used for calibration of the CFD results. A well calibrated wind map can provide wind speeds at every location of the wind farm site. Accurate maps for the surface that slices through the turbine hub centers are essential for planning purposes, especially because of the strong dependence of wind speed on power. For the analysis, a rectangular footprint of land was considered that is oriented in the direction of the prevailing wind, with sufficient upstream and downstream distance from the existing core turbine region. Over 160,000 points of terrain height data were used for a 20km wide strip of land, with a resolution of 50m horizontally and 1m vertically. A mesh of one million hexahedral cells was generated. The grid was progressively coarsened in the vertical direction, with the first cell layer approximately 0.05m off the ground and gradually increasing to 25m in height at the top boundary of the domain. The prevailing wind was found to have a height-dependent profile taken from anemometer measurements at the site of the turbines. The measured velocity profiles were applied at the upstream inlet to the domain through the use of a user-defined function. Because the terrain is hilly near the site of the turbines, the resulting CFD predictions for velocity at the turbine site were greater than the measured values by about 50% in the initial runs. By calibrating the inlet profiles using the measured velocities at the turbine, the adjusted predictions at the turbines were brought to within 10% of the measured values. By repeating this process, using anemometer data from other nearby turbines and re-calibrating the inlet profiles, the wind speed map was developed into an accurate tool for predicting the flow field at all locations at the site. This project will allow the company to explore further the potential of CFD, to improve knowledge of wind conditions at existing and prospective sites. ■ © Crown Copyright Land topography used as a boundary for the simulations 8 Fluent NEWS spring 2002
environmental UK Water Seminar on Tap by Robert Harwood, Fluent Europe In December, Fluent Europe Ltd. held a seminar on CFD in the Water Industry. With the generous assistance of Anglian Water, the seminar took place at Grafham Water Treatment Works. Grafham Water is one of the largest man-made lakes in Europe. It contains nearly 13,000 million gallons (59 million cubic meters), has a perimeter of 10 miles (16km), and at its deepest is 70 feet (21 meters). The site has been landscaped and considerable effort has been made to ensure that the public is able to enjoy the beauty and leisure opportunities of Grafham Water, while Anglian Water goes about the business of treating and delivering water to its customers. Grafham Water Treatment Works can deliver up to 360 million liters of water a day with an average daily supply of 230 million liters. The seminar opened with an introduction and welcome to Grafham and a general presentation on Fluent and CFD before the day’s proceedings got underway. Dr. Jim Wicks described some of the major CFD projects that had been undertaken by Anglian Water, and these included: • validation of CFD predictions against laboratory data for a service reservoir, • how £60,000 had been saved in pipework costs by using CFD in a service reservoir optimization study, and • how a 25% improvement in final water quality had been achieved by recommending a change in dosing location. Dr. Mike Faram then talked about how FLUENT was used at Hydro – a leading supplier of novel and innovative separation and flow control devices to the worldwide water industry. Their range of products includes the Hydrobrake ® Flow Control, Stormcell ® storage media, screening systems such as the Hydro-Jet screen, and a range of hydrodynamic separators such as the Gritking ® and Stormking ® . A novel design of combined sewer overflow (CSO) chamber, the StormFox, was introduced by Russ Currie of Johnston Pipes Ltd. The role of Fluent CFD software in fast tracking the design process was discussed. Following a demo of FLUENT 6.0, the delegates were taken on a tour of the works, providing a suitable end to a very enjoyable day. • Some of the delegates at the seminar after the tour around Grafham Water Treatment Works, with the anthracite, sand and garnet (ASG) filters in the background. Grafham Water (courtesy of Anglian Water) Fluent NEWS spring 2002 9
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Wind Turbine

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