2.6 气流原理 Air current principle

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力学湍流/涡流的原理 Mechanical turbulence /Eddy currents

力学湍流由运动的空气与地球表面的摩擦而形成。这个磨擦会引起涡流,涡流会从地表向上扩张,这个扩张的高度依风速,地表的粗糙程度和空气的稳定性。Mechanical turbulence is caused by friction between moving air and the earth surface. The friction causes eddy currents in the air, which extend upwards from the surface of the earth. The vertical extent of these currents depends on the wind speed, roughness of the terrain and stability of the air.

地面造成的磨擦和湍流会降低地表风的速度,这就是为什么高度越高,风速越快,The ground creates friction and turbulence which greatly reduce the speed of wind that close to ground. This is why wind becomes stronger at greater heights from the ground.

在障碍物的上风向和下风向,风速还会因湍流和涡流被继续减弱,减弱的模式如下图作为参考。The wind speed on the windward and leeward side of an obstruction will also be reduced as indicated in following figure because of the turbulence and eddies.

在障碍物的下风向,湍流和涡流的形成是因为,当风吹过障碍物时,在它的下风向的这个一定长度的区域内形成一个巨大的负压区,这样就有部分空气被吸入来填补这一空缺。这一区域的长度大致为障碍物高度的10-15倍。障碍物下风向的湍流和涡流的多少要依障碍物的种类。如越坚固平整的障碍物如建筑,比粗糙或有孔隙的障碍物如树林和植被区,会产生更多的涡流。

When wind pass obstruction, turbulence and eddy currents will be formed in leeward where a huge low pressure area is created and causes the wind to curl in to fill the void. The area is 10-15 times of the height of the obstruction. The amount of turbulence downwind of an obstruction will depend on the type of obstruction involved. A solid obstruction such as a building will have strong eddy winds downwind of the building. Porous obstructions, such as trees and vegetation, allow some wind to pass through them and will have fewer eddies downwind.

如果垃圾场已成小山,它就成为风的障碍物,所以在它的湍流/涡流区,气味就很难扩散出去,这就是为什么有时,在垃圾场下风向的某一区域,气味持续不散的原因。So, if landfill has become a hill, it becomes a obstruction to the wind and the turbulence /Eddy currents could make the odor be hard to be removed in some area of the leeward. This is why, sometimes, people who live in the leeward of landfills can smell constant malodor.

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