Richard J.A.M. Stevens

Physics of Fluids

University of Twente

Publication 73 · Wind-farm flow

Why the first turbine row is not an isolated reference

J.M.I. Strickland and R.J.A.M. Stevens, Journal of Physics: Conference Series 1618, 062069 (2020).

The article and figure are open access under CC BY 3.0.

Main finding

In the tested spanwise-infinite arrays, tight lateral spacing increased first-row power relative to an isolated row, while seven downstream rows decreased it. These opposing layout effects mean that a wind farm's first row is not a neutral reference for blockage or total-farm performance.

First-row wind-farm power relative to a free-standing turbine versus thrust coefficient for three streamwise spacings
How to read the figure. Both panels compare the average first-row turbine power with a free-standing reference. Blue squares, green triangles, and red circles denote streamwise spacings sx = 1.96, 3.93, and 7.85, respectively. The closest rows remain below the reference, while the two wider spacings rise above it as thrust increases. The left and right panels use CT and C′T, respectively. Error bars show the reported block-averaging uncertainty; dashed curves combine fits from the separate lateral-row and downstream-row comparisons rather than independent fits to these points. Open the full-resolution figure. Figure 4, cropped. J.M.I. Strickland and R.J.A.M. Stevens (2020), CC BY 3.0.

Why this matters

A first-row turbine is often used as the reference for downstream losses, but it already responds to its neighbors. In these arrays, tight lateral packing benefits the row relative to a free-standing turbine, whereas downstream rows reduce its power. Combining the effects makes the net first-row change depend on layout and thrust, so first-row normalization can conceal which interaction is responsible.

Research context

The comparison uses neutral offshore-boundary-layer large-eddy simulations with 100 m actuator disks, two unusually tight lateral spacings, three streamwise spacings, and eight-row arrays that are periodic and therefore infinite in the spanwise direction. Turbine power is actuator-disk work rather than electrical power, and only the farm's first row is analyzed—not downstream-row or total-farm power. The proposed lateral-confinement and over-farm-diversion mechanisms are physically plausible interpretations, but the article reports no pressure, velocity, streamline, or mass-flux fields that would isolate them. The percentages are therefore not general blockage corrections for finite commercial farms.

Read the article Open-access version View in the complete publication list Related wind-farm LES research