[shovel]

I was doing some acoustics work (horn design) a few days ago and, being aware that acoustics and aerodynamics are effectively the same as each other, it occurred to me that there could be some benefit to applying capacitance to the wake area of a vehicle moving through air.

Being more specific, a blunt-tailed vehicle traveling through air at a given speed will leave behind a low pressure wake, and that wake will inherently resonate in the same way that a bottle resonates when you blow across it or a vented speaker enclosure resonates. This is why, for example, a tarp would flap about if you dragged it behind your vehicle.

If you could isolate the fundamental frequency of that resonant wake at a given target (air) speed (65mph? ) it would be possible to build a cabinet, chamber, whatever you want to call it that resonates at the same frequency and may significantly clean up the vehicle's wake as a result.

As an example, if you had a SUV whose wake naturally resonates at 7hz and you could build a lightweight "backpack" to fit inside its tailgate (you choose if you want the ugly part inside or outside the vehicle) occupying 30 cubic feet, with a vent around 16 square inches cross-section and 54 inches deep - that should go a long way toward cleaning up the shape of the vehicle's wake. However, that's a pretty huge enclosure with a difficult to manage vent! By cutting the enclosure size down to 10 cubic feet, with 16 square inches of vent 18 inches deep... you lose some effectiveness but the size becomes easier to manage - thankfully reality is fractal so there is a lot of room for optimization.

Since the wake's resonant frequency is completely dependent upon airspeed, air direction and the shape of the vehicle it would be most useful if some mechanical means were employed for tuning the helmholtz resonator in realtime, potentially using the same type of feedback system employed in noise cancelling headphones or simply an aircraft-type pitot speedometer.

So - any other thoughts on this?

I have no plans to build such a creature in the near future, it just seemed a novel approach I haven't seen anyone propose before so I wanted to submit it for discussion.