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

As it can be seen from figures number 2.5 and 2.6, the increase of the heightdistribution factor seems to be not responsible of the variation of the verticalprofiles. Anyhow, a better accuracy of the results is obtained, as a general rule, forlow values of the HDF, which moves the vertical central cell points in a region closerto the ground, where velocity gradients are higher.Figure 2.7: Zoom of the figure 2.5.Figure 2.6 shows that the three curves don’t overlap completely, as it can be seenalso from the zoom in the further figure 2.7.The phenomenon shown in figure 2.7 is very important, and must be taken intoaccount when working with wind data measured at low height respect to the groundlevel. So it’s reasonable to run simulations with low values of height distributionfactor when a particular precision near the ground level is needed, while insituations regarding the evaluation of the wind resources at high levels thisphenomenon becomes less marked. The experience shows, moreover, that theheight distribution factor cannot be decreased indefinitely, but its value is strictlyconnected to the resolution of the horizontal grid. Then, if it is necessary to havegood precision in such low heights, also the dimension of the horizontal cells must21