Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An entrainment-based model for annular wakes, with applications to
  airborne wind energy   Several novel wind energy systems produce wakes with annular cross-sections,
which are qualitatively different from the wakes with circular cross-sections
commonly generated by conventional horizontal-axis wind turbines and by compact
obstacles. Since wind farms use arrays of hundreds of turbines, good analytical
wake models are essential for efficient wind farm planning. Several models
already exist for circular wakes; however, none have yet been proposed for
annular wakes, making it impossible to estimate their array performance. We use
the entrainment hypothesis to develop a reduced-order model for the shape and
flow velocity of an annular wake from a generic annular obstacle. Our model
consists of a set of three ordinary differential equations, which we solve
numerically. In addition, by assuming that the annular wake does not drift
radially, we further reduce the problem to a model comprising only two
differential equations, which we solve analytically. Both of our models are in
good agreement with previously published large eddy simulation results.

34
The categories of this paper are: chem-ph
11
The categories of this paper are: hep-lat
16
The categories of this paper are: stat
2
The categories of this paper are: math
29
The categories of this paper are: funct-an
15
The categories of this paper are: nucl-ex
13
The categories of this paper are: quant-ph
6
The categories of this paper are: astro-ph
31
The categories of this paper are: ao-sci
18
The categories of this paper are: econ
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc
4
The categories of this paper are: cond-mat
17
The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th