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Sources I've read contains contradicting information. As far as I know, when the laminar airflow breaks up, it becomes a thicker and draggy layer, causing a layer of what essentially is slowed air; this would suggest a reduction in kinetic energy, however some books have stated that it is actually an increase.....?

This makes what seems to be a simple concept to be hard to grasp, personally I see it as a reduction in KE, but the books say otherwise. So if anyone knows what happens to KE in a turbulent layer, that'd be greatly appreciated.

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Energy is transferred from the moving airplane's skin into the air in the turbulent boundary layer. Because the layer is turbulent, all the momentum vectors for every little parcel of air entrained in the layer are pointing in random directions with some uniform component (in the direction of the plane's travel) superimposed.

Thus the air in that layer gets vigorously stirred up, and since air has viscosity, the stirring action gets fairly quickly transformed into frictional heat. So after the plane has departed out of the picture, the turbulence and net motion in its wake get dissipated and the air is left a little warmer than it was before the plane flew through it.

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  • $\begingroup$ In the reference frame of the aircraft, no energy can be transferred from it (work is force times distance and the wing isn't moving). In that all the extra energy is at the expense of the pressure energy, which is why turbulent layer increases lift and delays separation (stall). Of course pressure is independent of reference frames. $\endgroup$ – Jan Hudec May 3 at 7:10

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