wind energy resource evaluation in a site of central italy ... - WindSim

Analyzing RMS error table for tower 5424, it is found that the sectors whereturbulence intensity level is higher is 240°, during both periods April-May andNovember-December. Sectors where turbulence intensity is lower are sector 180°and 60°, respectively for periods April-May and November-December. Byconsidering the RMS table and the U30 table, different behaviors for the twoperiods of reference can be found. In fact, during April-May the error seems toincrease with the wind speed, while during November –December the error seemsto decrease when U30 is growing. This behavior is well represented by the trendlines shown in figure 6.7.In general, it can be stated that the values of the T.I. seem to be strongly linked tothe seasonal thermal effects. As was already said before, the solar radiation and thethermal inertia of the terrain can generate different wind breezes in themeasurement periods, also influencing the turbulence level. A stronger influence onthe turbulence intensity level can be due also to the orographic effects. The tower5424 is placed in a cliff, where vertical component of velocity are present and can bestrongly variable in intensity during the whole year because of the different solarradiation. Particularly, strong solar radiation near a cliff can generate a intensevertical wind, where the fluctuations are stronger. This phenomenon could explainthe trend relative to April-May period in figure 6.7, where in general the errorsincrease with the U30.Finally, it must be said that turbulence is a parameter very difficult to measure,especially in atmospheric flows, and that a only a longer measurement campaigncan guarantee more accurate results. Due to all this consideration, the agreementbetween experimental data and CFD results for mast 5424 was fairly good.104