Wake structure measurements at the Mod-2 cluster test facility at Goodnoe Hills

Abstract

A field measurement progam was carried out at the cluster of three MOD-2 wind turbines located at Goodnoe Hills, Washington, to determine the rate of decay of wake velocity deficit with downwind distance in various meteorological conditions. Measurements were taken at hub height (200 ft) between July 12 and August 1, 1982. Wake wind speeds were measured using a radiosonde suspended from a tethered balloon, its position being determined from a grid of ground stakes. Measurments were also made downwind with the turbine off to determine the magnitude of terrain-induced variations in wind speed. The balloon system used to measure downstream wind data proved to be reliable and convenient. Downstream distances of 900, 1500, 2100, and 2700 ft from the turbine were investigated. Differences between the instrumentation systems required that corrections be made to the data. After correction, averaged terrain-induced wind speed variations were regarded as insignificant. Turbine-on velocity ratios showed scatter, suggesting that only some measurements were, in fact, representative of wake centerline velocities, and that others were made off centerline due to wake meander or wind shift. Isolation of the high wind speed (30 to 45 mph) velocity ratios, however, revealed velocity deficits downstream. Measurements at greater downstreammore » distances showed no wake deficit within the limits of resolution of the experiment, indicating that the wake had recovered to free stream conditions. Comparison with the AeroVironment wake model using common values for rotor drag coefficient and turbulence showed similar trends.« less

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