Wind farm blockage and edge effects: A wind tunnel study.

An experiment was conducted inside the UTD-BLAST wind tunnel to study the flow evolving across a wind farm for different numbers of rows, N_r. Porous disks with a hub height of 8 cm and a diameter, D = 4 cm were used to set up either aligned or staggered configurations. Wind speed at different turbine locations was indirectly estimated using thrust measurements from a 1-D force sensor installed at the hub of the turbines. Results show that the increasing number of downstream rows causes a larger blockage effect i.e., more wind speed reduction for the disks at the first row. This effect is more pronounced for the staggered configuration. For both cases, the decrease in wind speed becomes asymptotic when N_r > 5. In the aligned configuration, the reduction is 2.5% compared to the single-row configuration, while in the staggered configuration, it is 3.0%. For configurations with N_r ≥ 5, the turbines situated at the edge encounter greater wind velocity in comparison to the other turbines in the same row. In an aligned configuration with N_r = 13, at row 10, the turbine at the edge encounters about 13% higher wind speed. Once a fully developed flow regime is achieved (with configurations having N_r >11), the row average wind speed at the exit row is about 1-2% higher than the previous row.