I’m trying to figure out what happens to wind when you extract energy from it, specifically by going past a wind turbine.
Before hitting the turbine the air has an amount of kinetic energy, based on its mass and (squared) velocity. The turbine takes some of that energy out. So, is the departing air just moving slower? But if you had air coming towards the turbine faster than it departs on the other side, wouldn’t that mean an accumulation of air around or behind the turbine? I’m guessing the flow is more complicated than that, and results in turbulence somewhere.
Does the air maybe lower in temperature? The pressure change? What other results might there be of the energy being removed?
If I had to guess (since I don’t know anything about fluid dynamics), I’d guess that it comes it at low pressure and leaves at a high pressure and that would somehow account for it being able to leave at a lower speed. IOW (maybe) the air leaves more dense then it entered.
The temperature would, I assume, go up, but I think it’s really more about the density in this case.
It’s the other way around. Normally, the extraction of kinetic energy would manifest as a decrease in wind speed, but, as you say, the wind velocity has to be the same immediately before and immediately after it hits the turbine, or it would pile up, so it manifests as a pressure decrease instead. This creates turbulence, which is why wind farms are as spread out as they are. Sometimes it happens, because the wind can come from any direction, but you really don’t want one turbine to be immediately downstream of another.
Whew! It’s been a while, more than 35 years, since I dealt with that stuff. Maybe I understood half?
Of what I did understand, I think the net result is a lower temperature downstream of the turbine. There is a localized pressure loss which produces a lower temperature. The lower pressure results in pulling air from above, below, and downstream. The overall speed of the wind, however, is a result of a pressure difference between point A (upstream of the turbine) and point B, far enough downstream as to not be affected by the turbine. As these two pressures are not affected by the turbine, energy from the turbine must have come from the heat content of the atmosphere.
