Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Potential order-of-magnitude enhancement of wind farm power density via
  counter-rotating vertical-axis wind turbine arrays   Modern wind farms comprised of horizontal-axis wind turbines (HAWTs) require
significant land resources to separate each wind turbine from the adjacent
turbine wakes. This aerodynamic constraint limits the amount of power that can
be extracted from a given wind farm footprint. The resulting inefficiency of
HAWT farms is currently compensated by using taller wind turbines to access
greater wind resources at high altitudes, but this solution comes at the
expense of higher engineering costs and greater visual, acoustic, radar and
environmental impacts. We investigated the use of counter-rotating
vertical-axis wind turbines (VAWTs) in order to achieve higher power output per
unit land area than existing wind farms consisting of HAWTs. Full-scale field
tests of 10-m tall VAWTs in various counter-rotating configurations were
conducted under natural wind conditions during summer 2010. Whereas modern wind
farms consisting of HAWTs produce 2 to 3 watts of power per square meter of
land area, these field tests indicate that power densities an order of
magnitude greater can potentially be achieved by arranging VAWTs in layouts
that enable them to extract energy from adjacent wakes and from above the wind
farm. Moreover, this improved performance does not require higher individual
wind turbine efficiency, only closer wind turbine spacing and a sufficient
vertical flux of turbulence kinetic energy from the atmospheric surface layer.
The results suggest an alternative approach to wind farming that has the
potential to concurrently reduce the cost, size, and environmental impacts of
wind farms.

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The categories of this paper are: quant-ph
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The categories of this paper are: q-alg
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The categories of this paper are: bayes-an
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The categories of this paper are: stat
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The categories of this paper are: adap-org
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The categories of this paper are: hep-ph
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The categories of this paper are: solv-int
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The categories of this paper are: mtrl-th
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The categories of this paper are: gr-qc
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-th
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: ao-sci
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The categories of this paper are: econ