Evolution of Modern Wind Turbines Part A: 1940 to 1994 - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 161

Figure 3-38. Arrangement of the three Mod-2 HAWTs on the Goodnoe Hills site near
Goldendale, Washington. The triangular pattern permitted research on wake interference
effects at different downwind distances. ( Courtesy of Boeing Aerospace Corporation )
Three Mod-2 turbines were built and tested at the Goodnoe Hills site in order to
investigate initial problems associated with large-scale wind power stations and interactions
and interferences between multiple large wind turbines. The three turbines were placed in
a triangular pattern 5, 7, and 10 diameters apart such that wake interactions could be
examined under different spacings as changing wind directions placed the various units
behind one another (Fig. 3-38). Extensive use of anemometers as well as kites, smoke,
balloons, and other techniques were used to characterize the local wind low over the site
in detail.
As in any high-risk technological advance, a number of problems were encountered,
particularly during the irst two years of operation. These included fatigue cracks in the
turbine shafts originating at component mounting holes, contaminated hydraulic oil, and
leaking grease seals causing premature failure of blade tip support bearings. While these
dificulties caused signiicant delays and costs because of the size of the components and
the necessity to special-order or fabricate each part, the turbines themselves operated
according to design. Investigations continued into operating strategies and control
algorithms, to increase energy capture and reduce structural loads.
Other modiications were made to improve the Mod-2 system, based on experience
gained during the program. For example, lines of small vortex generators were installed
on the low-pressure side of the blade, which delayed low separation, enhanced control
stability, and signiicantly increased energy capture. As a result, the turbine produced more
power than its design predictions, in spite of the tips operating at higher angles of attack
than expected.
One problem that was directly associated with the design of the wind turbine was that
rotor cyclic loads were higher than calculated. While no structural failures occurred, the
Mod-2 rotor as built would probably have had an approximately 10-year fatigue life, rather
than the 30-year design value. It was felt that the rotor could be redesigned for a 30-year
life, based on continued research which has shown the foundations of the problem. The
structural loading estimates of that time used overly-simpliied models of the wind. The