  We present a suite of large-eddy simulations of a wind farm operating in
conventionally neutral atmospheric boundary layers (CNBLs). A fixed 1.6 GW wind
farm is considered for 40 different atmospheric stratification conditions to
investigate effects on wind-farm efficiency and blockage, as well as related
gravity-wave excitation. A tuned Rayleigh damping layer and a wave-free fringe
region method (Lanzilao & Meyers, Bound. Layer Meteor. 186, 2023) are used to
avoid spurious excitation of gravity waves, and a domain-size study is included
to evaluate and minimize effects of artificial domain blockage. A fully neutral
reference case is also considered, to distinguish between a case with
hydrodynamic blockage only, and cases that include hydrostatic blockage excited
by gravity waves. We discuss in detail the dependence of gravity-wave
excitation, flow fields, and wind-farm blockage on capping-inversion height,
strength and free-atmosphere lapse rate. In all cases, an unfavourable pressure
gradient is present in front of the farm, and a favourable pressure gradient in
the farm, with hydrostatic contributions arising from gravity waves at least an
order of magnitude larger than hydrodynamic effects. Using respectively
non-local and wake efficiencies $\eta_\textit{nl}$ and $\eta_\textit{w}$
(Allaerts & Meyers, Bound. Layer Meteor. 166, 2018), we observe a strong
negative correlation between unfavourable upstream pressure rise and
$\eta_\textit{nl}$, and a strong positive correlation between the favourable
pressure drop in the farm and $\eta_\textit{w}$. Using a simplified linear
gravity-wave model, we formulate a simple scaling for
$\eta_\textit{nl}/\eta_\textit{w}$, which matches reasonably well with the LES
results.
