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All flows around an object create Karman vortex streets in its wake. It doesn't matter what you do to limit the vortices. You can't stop them from happening, just like you can't stop resonance from happening. You can only dampen by destructive interference.

Birds use their flapping wings to shed vortices and ride the airflow they create, through the Karman wake.

https://www.youtube.com/watch?v=u8vyMHX9KNw

Here you see a starting vortex on the high pressure side of an airfoil, you see the vortex that is shed in effect entrains air over the low pressure side. In other words the vortex is sucking air over the low pressure side, accelerating it along the curvature of the wing.

Birds can keep their wings in sync with the movement of these "starting" vortices, fixed wing craft cannot.

Therefore fixed wing craft are more prone to perturbations from Karman wakes.

Even at extremely high Reynolds numbers we see Karman wakes https://www.youtube.com/watch?v=LfDyIB6J8kM

And also at very low Re# https://www.youtube.com/watch?v=k9FPxuhFlTo

The point of all of this is that if you want to reduce drag, or have more control over the wake vortices, then you have to play with geometry, length, leading edge thickness.

The stronger the trailing wake vortex, especially around a bluff body, the higher the drag, breaking up those trailing wake vortices can reduce drag. Preventing leading edge vortices can in some instances make trailing edge vortices more severe, in other cases less severe, depending on length and leading edge thickness.

https://youtu.be/ZCbZZ8OpP-g?t=61

All flows around an object create Karman vortex streets in its wake. It doesn't matter what you do to limit the vortices. You can't stop them from happening, just like you can't stop resonance from happening. You can only dampen by destructive interference. Birds use their flapping wings to shed vortices and ride the airflow they create, through the Karman wake. https://www.youtube.com/watch?v=u8vyMHX9KNw Here you see a starting vortex on the high pressure side of an airfoil, you see the vortex that is shed in effect entrains air over the low pressure side. In other words the vortex is sucking air over the low pressure side, accelerating it along the curvature of the wing. Birds can keep their wings in sync with the movement of these "starting" vortices, fixed wing craft cannot. Therefore fixed wing craft are more prone to perturbations from Karman wakes. Even at extremely high Reynolds numbers we see Karman wakes https://www.youtube.com/watch?v=LfDyIB6J8kM And also at very low Re# https://www.youtube.com/watch?v=k9FPxuhFlTo The point of all of this is that if you want to reduce drag, or have more control over the wake vortices, then you have to play with geometry, length, leading edge thickness. The stronger the trailing wake vortex, especially around a bluff body, the higher the drag, breaking up those trailing wake vortices can reduce drag. Preventing leading edge vortices can in some instances make trailing edge vortices more severe, in other cases less severe, depending on length and leading edge thickness. https://youtu.be/ZCbZZ8OpP-g?t=61

(post is archived)

[–] [deleted] • 1 pt

I'm likely totally wrong so take this with a grain of salt. If the vortecies cause drag then remove them by creating extra air intake to suck in them and use them as extra propulsion like a ramjet in the wings would seem to take away after lift but remove before vortice creation like a horizontal scoop on the wing and like NASCAR's drafting their is likely a way for existing pressure in the engine to pull in that air from the wings into the propulsion system to create more pressure for thrust. Might have to take some fuel tanks and relocate them but it would be worth it if drag was significantly reduced in the process.

[–] • 1 pt

So in other words, you're saying create a low pressure field in front of the craft so that there's no air resistance? Torpedoes do this with cavitation bubbles that form in front. In effect that's what a propeller does, it creates a separation of low vs high pressure and in this separation there's flow. If you want air to flow, you have to create a pressure separation, but when you create that pressure separation you get vortices, it's unavoidable.

To create that pressure separation takes energy, and the motion is extremely consistent, high pressure always goes to low. The turbo in fact creates a large draw of air, the boost pressure generated by the turbo isn't consistent however, so the laminar flow created by turbo suction would be inconsistent. Exhaust blown diffusers work, but the effect is too inconsistent, because the throttle varies a lot during the corners where the downforce is needed most.

[–] [deleted] • 1 pt

Thanks for the detailed thought out reply, I kind of understand it which is a lot more than I realized before it that's for sure.