this post was submitted on 24 Aug 2024
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How would a turbine that takes energy from the air current generated by a passing car decrease the energy of the car? The car has imparted the energy to the air, the air has already extracted energy from the car aerodynamic or directly Newtonian forces, and then the turbine would extract energy from the accelerated air from the passing vehicles.
IIRC there was a real world test of this idea some time ago and the results weren’t great. But imagine you do this in a tunnel- that will help improve the results and answer your question.
If you’ve ever been in a subway you’ve probably noticed the train pushes a wall of air ahead of itself. This is the energy you would need to capture. But by “capturing” it, you would inherently increase resistance on the airflow, and therefore the vehicle.
The reason you can’t imagine this being an issue in a typical roadside is the same reason the effect yields poor results. There is little in the way of channeling the air across the turbines, which also means there is little resistance on the passing vehicles. Of course the air in the atmosphere, pushing against the air your car moves ahead of itself, is the classic example of this overall effect.
I think the turbine would have to be close enough to slow the airflow boundary layer increasing drag on the moving train and/or cause tbe train to need to re-accelerate slowed air, and that would have to be uncomfortably close turbines. We’re not even getting into the weeds about the drag cause by the tunnel walls and any structure protruding from it, or how aerodynamic the train is in the first place yet.
Cars are as you point out a completely different animal, and the effect of any turbines would affect the next passing car only if a) the car were close enough to benefit from the “draft” of the preceding car, and b) if a is true, then it would lose energy re-accelerating air energy lost to the turbine.
I actually did give it more than a passing thought, and even if it’s just an esoteric discussion, the energy losses wouldn’t be worth calculating, and the gains minimal.
Not sure where you got that idea from, but how would that generate a meaningful amount of energy? It seems very unlikely that such a system would ever recover the energy spent on its construction.
I think it’s because you said, “Any system that gains some energy from a passing car,” not that anyone mentioned turbines explicitly.