Most modern windmills appears to rotate clockwise. I know that is has something to do with the direction were the wind is coming from. But how to understand this?


It is to do with the angle of the blade, it has nothing to do with the direction of the wind. If the blade is slightly facing clockwise then the wind will push it to turning anticlockwise. If the blade is slightly facing anticlockwise then the wind will push it up and become clockwise. There is no reason from a physics perspective that governs which direction of rotation is best. Modern wind turbines are manufactured in factories who use the same design of blades, this can reduce the cost of production and present a coherent view. While windmills in the past are produced in small local subsistence workshop and don't have standardization.

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    $\begingroup$ It might even go back to the fact that (most) aircraft propellors rotate clockwise, or indeed, to the fact that most clocks rotate clockwise. No reason beyond one person starting out that way, and lots of others following until it becomes a habit. $\endgroup$ – jamesqf Mar 6 '17 at 19:27
  • $\begingroup$ -1 There are quite a few reasons for choosing CW or CCW rotation, see the answer to this question. On top of these, Coriolis force also comes to mind, which produces wear in different place depending on CW or CCW rotation. $\endgroup$ – milancurcic Mar 6 '17 at 20:43
  • $\begingroup$ @milancurcic I'm pretty sceptical about some of the things mentioned in the answer that you link. As for Coriolis force... I haven't done the maths, but is it going to be noticable at the scale of a wind turbine? Even one that is facing north or south? :-) $\endgroup$ – Semidiurnal Simon Mar 11 '17 at 16:25
  • $\begingroup$ @SimonW Me too but I'm hoping this answer can be improved by including references. If the reason is purely historical, then there should exist records to support this. Coriolis acts on all scales. The effect is probably not significant for the lifetime of a turbine, and is very likely accounted for in the design (which is what this question is about). E.g. railroad tracks wear unevenly further from the Equator. I am not an engineer, just challenging unsupported blanket statements here. :) $\endgroup$ – milancurcic Mar 11 '17 at 18:21

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