Quote:
Originally Posted by freebeard
What do you think of this one. I made it for another thread in 2015 -- a bellmouth difusser.
One big vortex generator to order the wake.
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An interesting idea. If you are heating the air in the center, this is effectively a turbine that produces thrust!
By the way, generally speaking, one wants to avoid sharp / cleaving edges at the front of a vehicle. The reason is because air rarely is coming on exactly straight along the main axis. Even modest crosswinds (10 mph) at highway speeds (65 mph) create angles that sharp edges shadow... and thus produce lots of counterproductive turbulence. If we look at real turbines:
https://storage.googleapis.com/mcp_2...-1920x1000.jpg
we can see that the leading rim is always a rounded shape. The reason why rounded fronts/noses are universal is because they still function well even when airflow is off angle to their primary axis.
The other reason why we want round noses instead of sharp edges is they also produce the lowest drag, when integrated by off angle. A way to produce low drag is to have the smallest area being "pushed back" against airflow. In a curved nose, that's basically a knife edge for an aerofoil and a tip for missile. If air comes off angle, the high pressure area is still small. But in a sharp / angular / flat surface, when air comes off angle, it often exposes some surface * some trig function that produces appreciable counterforce.
That's actually the biggest mistake I made when I first started my mods. I only thought in the two dimensions of the car silhouette, instead of the full 3D, let alone considering off axis flow. As Spock would say: "He is intelligent, but not experienced. His pattern indicates two-dimensional thinking."
As for the VGs, they produce turbulent flow and should be used with caution. The only use case where they are beneficial is when they reduce or prevent even worse turbulent flow. Their best use is to try to reattach separated flow earlier to a surface than it would otherwise. If we introduce a VG into a laminar situation, it actually hurts performance. So, if the backside of your toroidal turbine already has a smooth tail with minimal wake, it's uncertain injecting turbulent air into it would actually help.