Editing Windbreak (section)

== Windbreak aerodynamics ==
[[Image:Bundesarchiv Bild 183-15117-0005, Infografik, Windschutz, Ertragssteigerung.jpg|thumb|An [[East Germany|East German]] windbreak promotion poster, 1952]]

When wind encounters a porous obstacle, such as a windbreak or shelterbelt, air pressure increases on the windward side and decreases on the leeward side. As a result, the airstream approaching the barrier is interrupted, and a portion of it moves over the barrier, resulting in a jet of higher wind speed. The remainder of the airstream then moves through the barrier to its edge downstream, pushed along by the decrease in pressure across the shelterbelt's width; as it emerges again, that airstream is interrupted further as its air pressure adjusts to the surrounding area. This results in slower wind speed further downwind, reaching a minimum at a distance of about 3 to 5 times the windbreak's height. Beyond that point wind speed recovers, aided by the overlying, faster-moving stream. From the perspective of the [[Reynolds-averaged Navier–Stokes equations]], these effects can be understood as resulting from the loss of momentum caused by the drag of leaves and branches and would be represented by the body force ''f<sub>i</sub>'' (a distributed momentum sink).<ref>{{cite journal |doi=10.1016/0167-6105(85)90001-7 |title=Numerical studies of flow through a windbreak |year=1985 |last1=Wilson |first1=John D. |journal=Journal of Wind Engineering and Industrial Aerodynamics |volume=21 |issue=2 |pages=119–154 }}</ref>

Windbreaks reduce the wind's average air speed and make it less variable, resulting in the wind mixing less effectively than it does upwind. Additionally, all these changes to the wind's behavior result in changes to the region's environment. For instance, the [[surface energy budget]] of the ground may be impacted, as the slowed wind dissipates heat from the sun less effectively; this trend may reverse further downwind, and about 8 times the windbreak's height downstream, the windbreak may result in cooler surface temperatures.<ref>{{cite journal |doi=10.1016/0168-1923(89)90016-6 |title=The microclimate in the centre of small square sheltered plots |year=1989 |last1=Argete |first1=J.C |last2=Wilson |first2=J.D |journal=Agricultural and Forest Meteorology |volume=48 |issue=1–2 |pages=185–199 |bibcode=1989AgFM...48..185A }}</ref>