我不说话，只是科普"Popular" explanation based on equal transit-time 
An illustration of the (incorrect) equal transit-time theory
An explanation of lift frequently encountered in basic or popular sources is the equal transit-time theory. Equal transit-time states that because of the longer path of the upper surface of an airfoil, the air going over the top must go faster in order to catch up with the air flowing around the bottom, i.e. the parcels of air that are divided at the leading edge and travel above and below an airfoil must rejoin when they reach the trailing edge.Bernoulli's Principle is then cited to conclude that since the air moves faster on the top of the wing the air pressure must be lower. This pressure difference pushes the wing up.[40]
However, equal transit time is not accurate[41][42][43] and the fact that this is not generally the case can be readily observed.[44][45] Although it is true that the air moving over the top of a wing generating lift does move faster, there is no requirement for equal transit time. In fact the air moving over the top of an airfoil generating lift is always moving much faster than the equal transit theory would imply.[6]
The assertion that the air must arrive simultaneously at the trailing edge is sometimes referred to as the "Equal Transit-Time Fallacy".[46][47][48][49]
Note that while this theory depends on Bernoulli's principle, the fact that this theory has been discredited does not imply that Bernoulli's principle is incorrect.
http://en.wikipedia.org/wiki/Lift_(force) |
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发表于 2012-7-24 11:07
