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

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Figure 3.5: Development <strong>of</strong> the vertical pr<strong>of</strong>iles downstream the hill-top.Start<strong>in</strong>g from station 0, the flow is slow<strong>in</strong>g down until station 2: this behavior iscaused by the effect <strong>of</strong> the roughness (as expla<strong>in</strong>ed <strong>in</strong> chapter 2). Between station 2and station 3 the slow<strong>in</strong>g effect is stronger, due to the presence <strong>of</strong> the obstacle (thehill). When the flow passes over station 3, the hill geometry accelerates the flow,like <strong>in</strong> a subsonic convergent duct. The speed <strong>in</strong>crease is registered until the top <strong>of</strong>the hill, where the horizontal speed gets the maximum value.When the flow passes over station 6 (hill top), it sees a subsonic divergent duct andthe effect <strong>of</strong> slow down beg<strong>in</strong>s and cont<strong>in</strong>ues until station 9. The divergent channeltends to <strong>in</strong>crease the boundary layer more than the start<strong>in</strong>g value. Then gradually,the flow starts to accelerate aga<strong>in</strong>, <strong>in</strong> order to get the <strong>in</strong>itial conditions.A similar behavior <strong>of</strong> the flow over a hilly terra<strong>in</strong> can be found <strong>in</strong> [2]31

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