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Like others have said, there's no free lunch. Any time you extract work from the airstream you convert freestream air into drag. So whether by turbulance or an energy sucking pump, (turbine) work is being extracted from the ram air and creating a differential at the rear. This results in a minus energy situation known as drag. This drag is one of the reason the Sneider Cup race planes from the thirties did away with finned radiators and used smooth flat liquid filled panels along the sides and bottom of the fuselage instead. Heat transfere without as much drag. Any time you cause an acceleration (or bend airflow), you create drag.
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